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How do you focus regular light to make it a laser beam? | A laser beam is not just focused light. A laser beam is coherent light. Furthermore, you can't create a laser beam by cleverly focusing regular light, no matter how hard you try. You create a laser beam using stimulated emission. Stimulated emission is what causes the light in a laser beam to be coherent, and coherenc... | tag/electromagnetism/ | context: tag/electromagnetism/ question: How do you focus regular light to make it a laser beam? | A laser beam is not just focused light. A laser beam is coherent light. Furthermore, you can't create a laser beam by cleverly focusing regular light, no matter how hard you try. You create a laser beam using stimulated emission. Stimulated emission is what causes the light in a laser beam to be coherent, and coherenc... |
How is a magnetic field just an electric field with relativity applied? | This is a misconception. A magnetic field is not just an electric field with relativity applied, i.e. an electric field viewed from the wrong reference frame. In reality, a magnetic field is a fundamental field which can exist in a certain reference frame without needing any help from an electric field. More generall... | tag/electromagnetism/ | context: tag/electromagnetism/ question: How is a magnetic field just an electric field with relativity applied? | This is a misconception. A magnetic field is not just an electric field with relativity applied, i.e. an electric field viewed from the wrong reference frame. In reality, a magnetic field is a fundamental field which can exist in a certain reference frame without needing any help from an electric field. More generall... |
Is it possible to create magnetic waves? | Yes, it is possible to create electromagnetic waves using magnets. No, it is not possible to create magnetic waves without an electric field being present. Electric fields are created by electric charges. For instance, if you statically charged up a balloon by rubbing it on your hair, the balloon creates an electric f... | tag/electromagnetism/ | context: tag/electromagnetism/ question: Is it possible to create magnetic waves? | Yes, it is possible to create electromagnetic waves using magnets. No, it is not possible to create magnetic waves without an electric field being present. Electric fields are created by electric charges. For instance, if you statically charged up a balloon by rubbing it on your hair, the balloon creates an electric f... |
What makes heat rise? | Heat does not rise, hot air does (usually). Heat can spread out in all directions. There are three main ways for heat to travel: Thermal radiation tends to spread out in all directions and not just up. When you are standing a few steps back from a large campfire, most of the heat you are receiving is being delivered t... | tag/electromagnetism/ | context: tag/electromagnetism/ question: What makes heat rise? | Heat does not rise, hot air does (usually). Heat can spread out in all directions. There are three main ways for heat to travel: Thermal radiation tends to spread out in all directions and not just up. When you are standing a few steps back from a large campfire, most of the heat you are receiving is being delivered t... |
Why are there so many different kinds of forces in chemistry? | There is only one significant force at work in chemical reactions: the electromagnetic force. There are four fundamental forces in the universe: gravity, the electromagnetic force, the weak nuclear force and the strong nuclear force. Gravity is too weak to affect chemical reactions much, seeing as chemical reactions i... | tag/electromagnetism/ | context: tag/electromagnetism/ question: Why are there so many different kinds of forces in chemistry? | There is only one significant force at work in chemical reactions: the electromagnetic force. There are four fundamental forces in the universe: gravity, the electromagnetic force, the weak nuclear force and the strong nuclear force. Gravity is too weak to affect chemical reactions much, seeing as chemical reactions i... |
Why don't objects fuse to my finger when I touch them? | Objects always fuse to your finger when you touch them. You often don't notice this for two reasons: 1) Your finger is stronger than the object you are touching. When you pull away, you rip atoms off the object and these atoms remain fused to your finger as a microscopic residue. 2) Your finger is stronger than the bo... | tag/electromagnetism/ | context: tag/electromagnetism/ question: Why don't objects fuse to my finger when I touch them? | Objects always fuse to your finger when you touch them. You often don't notice this for two reasons: 1) Your finger is stronger than the object you are touching. When you pull away, you rip atoms off the object and these atoms remain fused to your finger as a microscopic residue. 2) Your finger is stronger than the bo... |
Why is gravity the strongest force? | Actually, gravity is the weakest of the four fundamental forces. Ordered from strongest to weakest, the forces are 1) the strong nuclear force, 2) the electromagnetic force, 3) the weak nuclear force, and 4) gravity. If you take two protons and hold them very close together, they will exert several forces on each othe... | tag/electromagnetism/ | context: tag/electromagnetism/ question: Why is gravity the strongest force? | Actually, gravity is the weakest of the four fundamental forces. Ordered from strongest to weakest, the forces are 1) the strong nuclear force, 2) the electromagnetic force, 3) the weak nuclear force, and 4) gravity. If you take two protons and hold them very close together, they will exert several forces on each othe... |
How can a material at a certain temperature have all of its molecules at the same energy? | A material at a certain temperature does not have all of its particles at the same energy. In the basic definition of the word, "temperature" is the average random motional (kinetic) energy of the particles of a material. (Thermodynamics gives a broader definition to temperature, but we don't need this definition here... | tag/energy/ | context: tag/energy/ question: How can a material at a certain temperature have all of its molecules at the same energy? | A material at a certain temperature does not have all of its particles at the same energy. In the basic definition of the word, "temperature" is the average random motional (kinetic) energy of the particles of a material. (Thermodynamics gives a broader definition to temperature, but we don't need this definition here... |
Light has no mass so it also has no energy according to Einstein, but how can sunlight warm the earth without energy? | Light indeed carries energy and accomplishes this without having any mass. The Einstein equation that you are probably referring to is E = mc2. This equation is actually a special case of the more general equation: E2 = p2c2 + m2c4 In the above equation, E is the total energy of the particle, p is the momentum of the ... | tag/energy/ | context: tag/energy/ question: Light has no mass so it also has no energy according to Einstein, but how can sunlight warm the earth without energy? | Light indeed carries energy and accomplishes this without having any mass. The Einstein equation that you are probably referring to is E = mc2. This equation is actually a special case of the more general equation: E2 = p2c2 + m2c4 In the above equation, E is the total energy of the particle, p is the momentum of the ... |
Since gravity is unlimited, can we use it as an infinite energy source? | No, gravity can not be used as an infinite energy source. In fact, strictly speaking, gravity itself can not be used as an energy source at all. You are confusing forces with energy, which are very different things. Energy is a property of objects, such as balls, atoms, light beams, or batteries. In contrast, forces d... | tag/energy/ | context: tag/energy/ question: Since gravity is unlimited, can we use it as an infinite energy source? | No, gravity can not be used as an infinite energy source. In fact, strictly speaking, gravity itself can not be used as an energy source at all. You are confusing forces with energy, which are very different things. Energy is a property of objects, such as balls, atoms, light beams, or batteries. In contrast, forces d... |
What are some other ways to save energy in a car besides turning off the air conditioner and rolling down the windows? | Turning off the air conditioner in a car and rolling down the windows actually uses more energy than driving with the windows up and the air conditioner on, if you are driving on the highway. The air conditioner uses very little energy. On the other hand, rolling down the windows introduces significant air resistance ... | tag/energy/ | context: tag/energy/ question: What are some other ways to save energy in a car besides turning off the air conditioner and rolling down the windows? | Turning off the air conditioner in a car and rolling down the windows actually uses more energy than driving with the windows up and the air conditioner on, if you are driving on the highway. The air conditioner uses very little energy. On the other hand, rolling down the windows introduces significant air resistance ... |
When does the breaking of chemical bonds release energy? | The breaking of chemical bonds never releases energy to the external environment. Energy is only released when chemical bonds are formed. In general, a chemical reaction involves two steps: 1) the original chemical bonds between the atoms are broken, and 2) new bonds are formed. These two steps are sometimes lumped in... | tag/energy/ | context: tag/energy/ question: When does the breaking of chemical bonds release energy? | The breaking of chemical bonds never releases energy to the external environment. Energy is only released when chemical bonds are formed. In general, a chemical reaction involves two steps: 1) the original chemical bonds between the atoms are broken, and 2) new bonds are formed. These two steps are sometimes lumped in... |
Why do diamonds last forever? | Diamonds do not last forever. Diamonds degrade to graphite, because graphite is a lower-energy configuration under typical conditions. Diamond (the stuff in wedding rings) and graphite (the stuff in pencils) are both crystalline forms of pure carbon. The only difference is the way the carbon atoms are arranged and bon... | tag/energy/ | context: tag/energy/ question: Why do diamonds last forever? | Diamonds do not last forever. Diamonds degrade to graphite, because graphite is a lower-energy configuration under typical conditions. Diamond (the stuff in wedding rings) and graphite (the stuff in pencils) are both crystalline forms of pure carbon. The only difference is the way the carbon atoms are arranged and bon... |
Why is light pure energy? | Light is not pure energy. While it is true that light has no mass, this fact does not imply that light is pure energy. Light is composed of fundamental quantum objects called photons which we list alongside other fundamental quantum objects such as electrons and neutrinos. Each object on this list contains several dif... | tag/energy/ | context: tag/energy/ question: Why is light pure energy? | Light is not pure energy. While it is true that light has no mass, this fact does not imply that light is pure energy. Light is composed of fundamental quantum objects called photons which we list alongside other fundamental quantum objects such as electrons and neutrinos. Each object on this list contains several dif... |
How did evolution ever lead ostriches to hide their head in the sand when an enemy approaches? | Ostriches never hide their head in the sand, especially not when approached by an enemy. In fact, ostriches can become quite aggressive when threatened. According to the book "Flightless Birds" by Clive Roots, ostriches respond to predators by either running away or attacking. Ostriches have very powerful legs and hav... | tag/evolution/ | context: tag/evolution/ question: How did evolution ever lead ostriches to hide their head in the sand when an enemy approaches? | Ostriches never hide their head in the sand, especially not when approached by an enemy. In fact, ostriches can become quite aggressive when threatened. According to the book "Flightless Birds" by Clive Roots, ostriches respond to predators by either running away or attacking. Ostriches have very powerful legs and hav... |
When did humans stop evolving? | Humans have never stopped evolving and continue to do so today. Evolution is a slow process that takes many generations of reproduction to become evident. Because humans take so long to reproduce, it takes hundreds to thousands of years for changes in humans to become evident. We simply don't notice the evolution of h... | tag/evolution/ | context: tag/evolution/ question: When did humans stop evolving? | Humans have never stopped evolving and continue to do so today. Evolution is a slow process that takes many generations of reproduction to become evident. Because humans take so long to reproduce, it takes hundreds to thousands of years for changes in humans to become evident. We simply don't notice the evolution of h... |
Why did evolution create a chicken that lays so many unfertilized eggs when that is so wasteful? | Natural evolution did not create a chicken that lays so many unfertilized eggs. Human engineering created such chickens. You could call the process "human-caused evolution", "artificial selection", or "selective breeding". The evolutionary principles of survival of the fittest and inheritance of genetic traits still a... | tag/evolution/ | context: tag/evolution/ question: Why did evolution create a chicken that lays so many unfertilized eggs when that is so wasteful? | Natural evolution did not create a chicken that lays so many unfertilized eggs. Human engineering created such chickens. You could call the process "human-caused evolution", "artificial selection", or "selective breeding". The evolutionary principles of survival of the fittest and inheritance of genetic traits still a... |
Why do humans crave sugary foods? Shouldn't evolution lead us to crave healthy foods? | Sugar is actually quite healthy when consumed in moderate amounts and in its natural form. The main natural source of sugar is fruit. In prehistoric times, vegetables were the most abundant foods and fruits were scarce in comparison. However, vegetables carry little energy compared to fruits. Therefore, the pre-human ... | tag/evolution/ | context: tag/evolution/ question: Why do humans crave sugary foods? Shouldn't evolution lead us to crave healthy foods? | Sugar is actually quite healthy when consumed in moderate amounts and in its natural form. The main natural source of sugar is fruit. In prehistoric times, vegetables were the most abundant foods and fruits were scarce in comparison. However, vegetables carry little energy compared to fruits. Therefore, the pre-human ... |
Why do humans have an appendix even though it is unnecessary? | The human cecal appendix is not completely unnecessary. In humans, the appendix is a small, dead-end tube that connects to the colon near where the small intestines feeds into the large intestines. Being a dead-end tube, the appendix can obviously not transport food and waste through the intestinal tract. Furthermore,... | tag/evolution/ | context: tag/evolution/ question: Why do humans have an appendix even though it is unnecessary? | The human cecal appendix is not completely unnecessary. In humans, the appendix is a small, dead-end tube that connects to the colon near where the small intestines feeds into the large intestines. Being a dead-end tube, the appendix can obviously not transport food and waste through the intestinal tract. Furthermore,... |
Why do my fingers absorb water and become wrinkled? | Human finger tips do not become wrinkled because they absorb water. Skin is a fairly good barrier that keeps out most of the external water. If our fingers did absorb a significant amount of water after staying in the pool or bath for several minutes, then our fingers would swell to round, plump shapes, which is the o... | tag/evolution/ | context: tag/evolution/ question: Why do my fingers absorb water and become wrinkled? | Human finger tips do not become wrinkled because they absorb water. Skin is a fairly good barrier that keeps out most of the external water. If our fingers did absorb a significant amount of water after staying in the pool or bath for several minutes, then our fingers would swell to round, plump shapes, which is the o... |
Why does evolution always lead to more advanced species? | Evolution does not always lead to more advanced species. Evolution is simply a description of the way change occurs in biological creatures over many generations in order to better exploit a certain environment. Evolution sometimes leads to progress, but it sometimes leads in the opposite direction. For instance, the ... | tag/evolution/ | context: tag/evolution/ question: Why does evolution always lead to more advanced species? | Evolution does not always lead to more advanced species. Evolution is simply a description of the way change occurs in biological creatures over many generations in order to better exploit a certain environment. Evolution sometimes leads to progress, but it sometimes leads in the opposite direction. For instance, the ... |
Why have humans evolved to be taller over the last three hundred years? | Humans have not evolved to be taller in the last three hundred years. While the average adult height has indeed increased in many countries over the last few hundred years, this increase was not caused by evolution. Additionally, the average height gain over the last few hundred years has not been very large. If you h... | tag/evolution/ | context: tag/evolution/ question: Why have humans evolved to be taller over the last three hundred years? | Humans have not evolved to be taller in the last three hundred years. While the average adult height has indeed increased in many countries over the last few hundred years, this increase was not caused by evolution. Additionally, the average height gain over the last few hundred years has not been very large. If you h... |
Can a fire have a shadow? | Yes, you can form the shadow of a fire, but perhaps not for the reason that you are thinking. A shadow is formed any time part of a light beam is blocked or redirected. The shadow region is the region in the light beam where there is less light than in the rest of the beam. This dimmer region tends to take on the shap... | tag/fire/ | context: tag/fire/ question: Can a fire have a shadow? | Yes, you can form the shadow of a fire, but perhaps not for the reason that you are thinking. A shadow is formed any time part of a light beam is blocked or redirected. The shadow region is the region in the light beam where there is less light than in the rest of the beam. This dimmer region tends to take on the shap... |
Can you light diamond on fire? | Yes, diamond can be burned. The most common form of burning in everyday life is carbon combustion. In carbon combustion, carbon atoms break their bonds with each other and with other atoms (which requires energy) to form bonds with oxygen atoms (which releases even more energy than first required). The net extra energ... | tag/fire/ | context: tag/fire/ question: Can you light diamond on fire? | Yes, diamond can be burned. The most common form of burning in everyday life is carbon combustion. In carbon combustion, carbon atoms break their bonds with each other and with other atoms (which requires energy) to form bonds with oxygen atoms (which releases even more energy than first required). The net extra energ... |
Do flames contain plasma? | The answer to this question is more complicated than most people realize. Some flames do contain plasma and some flames do not. To properly answer this question, we really have to first strictly define what we mean by "plasma". A textbook definition of a plasma is an ionized gas. "Ionized gas" means that some electron... | tag/fire/ | context: tag/fire/ question: Do flames contain plasma? | The answer to this question is more complicated than most people realize. Some flames do contain plasma and some flames do not. To properly answer this question, we really have to first strictly define what we mean by "plasma". A textbook definition of a plasma is an ionized gas. "Ionized gas" means that some electron... |
When I sit by a campfire, how does its hot air heat me? | When you sit by a campfire, most of the heat you are receiving from the fire does not come from hot air. It comes from thermal radiation. Generally, there are three ways that heat can travel: radiation, conduction, and convection. Thermal radiation consists of electromagnetic waves (mostly infrared waves and visible l... | tag/fire/ | context: tag/fire/ question: When I sit by a campfire, how does its hot air heat me? | When you sit by a campfire, most of the heat you are receiving from the fire does not come from hot air. It comes from thermal radiation. Generally, there are three ways that heat can travel: radiation, conduction, and convection. Thermal radiation consists of electromagnetic waves (mostly infrared waves and visible l... |
Why does the sun not run out of oxygen as it burns? | The sun does not run out of oxygen for the simple fact that it does not use oxygen to burn. The burning of the sun is not chemical combustion. It is nuclear fusion. Don't think of the sun as a giant campfire. It is more like a giant hydrogen bomb. In standard carbon combustion, carbon atoms in the fuel move up close t... | tag/fire/ | context: tag/fire/ question: Why does the sun not run out of oxygen as it burns? | The sun does not run out of oxygen for the simple fact that it does not use oxygen to burn. The burning of the sun is not chemical combustion. It is nuclear fusion. Don't think of the sun as a giant campfire. It is more like a giant hydrogen bomb. In standard carbon combustion, carbon atoms in the fuel move up close t... |
Can it rain fish? | Yes. Although rare, there are numerous instances of fish falling down from the skies. Of course, the fish do not really "rain" in the sense of condensing out of water vapor. The fish that fall from the sky are just fish that used to be in the sea. So what puts the fish up in the sky in the first place? Although few de... | tag/fish/ | context: tag/fish/ question: Can it rain fish? | Yes. Although rare, there are numerous instances of fish falling down from the skies. Of course, the fish do not really "rain" in the sense of condensing out of water vapor. The fish that fall from the sky are just fish that used to be in the sea. So what puts the fish up in the sky in the first place? Although few de... |
Can gravity form waves? | Yes, gravity can forms waves. Gravitational waves are ripples in spacetime that travel through the universe. If you think of gravity as a force acting at a distance, it is difficult to visualize how gravitational waves could form. However, if you use the more accurate description of gravity that was developed by Einst... | tag/gravity/ | context: tag/gravity/ question: Can gravity form waves? | Yes, gravity can forms waves. Gravitational waves are ripples in spacetime that travel through the universe. If you think of gravity as a force acting at a distance, it is difficult to visualize how gravitational waves could form. However, if you use the more accurate description of gravity that was developed by Einst... |
Does the influence of gravity extend out forever? | No. The attractive force called gravity does not extend beyond galaxy groups. If you look at Newton's Law of Universal Gravitation, you see that the force of gravity on one mass due to another mass depends on their separation r according to the dependence 1/r2. As you get farther away from a gravitational body such as... | tag/gravity/ | context: tag/gravity/ question: Does the influence of gravity extend out forever? | No. The attractive force called gravity does not extend beyond galaxy groups. If you look at Newton's Law of Universal Gravitation, you see that the force of gravity on one mass due to another mass depends on their separation r according to the dependence 1/r2. As you get farther away from a gravitational body such as... |
Does time go faster at the top of a building compared to the bottom? | Yes, time goes faster the farther away you are from the earth's surface compared to the time on the surface of the earth. This effect is known as "gravitational time dilation". It is predicted by Einstein's theory of General Relativity and has by verified multiple times by experiments. Gravitational time dilation occu... | tag/gravity/ | context: tag/gravity/ question: Does time go faster at the top of a building compared to the bottom? | Yes, time goes faster the farther away you are from the earth's surface compared to the time on the surface of the earth. This effect is known as "gravitational time dilation". It is predicted by Einstein's theory of General Relativity and has by verified multiple times by experiments. Gravitational time dilation occu... |
How can the heart be strong enough to pump blood up your legs against gravity? | The heart is not strong enough by itself to get the blood back up the veins in your legs and back to your heart. The human body relies on a second system to finish that task. This system involves small valves throughout the veins and muscle contractions from your skeletal muscles when you walk and move about. The valv... | tag/gravity/ | context: tag/gravity/ question: How can the heart be strong enough to pump blood up your legs against gravity? | The heart is not strong enough by itself to get the blood back up the veins in your legs and back to your heart. The human body relies on a second system to finish that task. This system involves small valves throughout the veins and muscle contractions from your skeletal muscles when you walk and move about. The valv... |
How does a cloud fill up with water? | Strictly speaking, a cloud does not fill up with water. First of all, a cloud is not a sponge made out of some other material which soaks up water. The water in a cloud is the cloud. More accurately, a cloud consists of very small liquid water drops or ice crystals suspended in air. The water drops and ice crystals th... | tag/gravity/ | context: tag/gravity/ question: How does a cloud fill up with water? | Strictly speaking, a cloud does not fill up with water. First of all, a cloud is not a sponge made out of some other material which soaks up water. The water in a cloud is the cloud. More accurately, a cloud consists of very small liquid water drops or ice crystals suspended in air. The water drops and ice crystals th... |
How does astrology work? | Hardened scientists will tell you astrology doesn't work. Believers will tell you it does. Who is right? They are both right. It depends on what you mean by the word "work". Astrology is the belief that the alignment of stars and planets affects every individual's mood, personality, and environment, depending on when ... | tag/gravity/ | context: tag/gravity/ question: How does astrology work? | Hardened scientists will tell you astrology doesn't work. Believers will tell you it does. Who is right? They are both right. It depends on what you mean by the word "work". Astrology is the belief that the alignment of stars and planets affects every individual's mood, personality, and environment, depending on when ... |
How does the expansion of the universe make outer space a vacuum? | The vacuum of outer space is not caused by the expansion of the universe, but is caused by gravity. First of all, when we say outer space (the space outside the atmosphere of planets and stars) is a "vacuum" or is "empty", we really mean that outer space is nearly empty or almost a perfect vacuum. In reality, even the... | tag/gravity/ | context: tag/gravity/ question: How does the expansion of the universe make outer space a vacuum? | The vacuum of outer space is not caused by the expansion of the universe, but is caused by gravity. First of all, when we say outer space (the space outside the atmosphere of planets and stars) is a "vacuum" or is "empty", we really mean that outer space is nearly empty or almost a perfect vacuum. In reality, even the... |
How does wind create all the ocean currents? | Ocean currents are mostly not created by wind. While wind can play a role, often minor, in shaping surface ocean currents, it is not the main or only factor. Furthermore, wind plays virtually no role at all when it comes to deep ocean currents. The main drivers of ocean currents are as follows: 1. The Coriolis Force. ... | tag/gravity/ | context: tag/gravity/ question: How does wind create all the ocean currents? | Ocean currents are mostly not created by wind. While wind can play a role, often minor, in shaping surface ocean currents, it is not the main or only factor. Furthermore, wind plays virtually no role at all when it comes to deep ocean currents. The main drivers of ocean currents are as follows: 1. The Coriolis Force. ... |
How high does a building have to be for a penny dropped from the top to kill a person on the ground? | Dropped pennies cannot kill people, no matter how high you drop them from. The reason is that air slows things down. Falling objects reach a maximum speed in air, called the terminal velocity, and can't go any faster. The less dense an object, the lower its terminal velocity. Think about letting go of a balloon from a... | tag/gravity/ | context: tag/gravity/ question: How high does a building have to be for a penny dropped from the top to kill a person on the ground? | Dropped pennies cannot kill people, no matter how high you drop them from. The reason is that air slows things down. Falling objects reach a maximum speed in air, called the terminal velocity, and can't go any faster. The less dense an object, the lower its terminal velocity. Think about letting go of a balloon from a... |
How large would a bucket of water have to be to put out the sun? | No amount of water thrown on the sun would cause it to go out. Instead, any amount of water would cause the sun to burn even more. The burning of the sun is nuclear fusion, not chemical combustion. Campfires and candle flames are examples of chemical combustion. In combustion, the electronic bonds between atoms are re... | tag/gravity/ | context: tag/gravity/ question: How large would a bucket of water have to be to put out the sun? | No amount of water thrown on the sun would cause it to go out. Instead, any amount of water would cause the sun to burn even more. The burning of the sun is nuclear fusion, not chemical combustion. Campfires and candle flames are examples of chemical combustion. In combustion, the electronic bonds between atoms are re... |
I know that the gravity of the moon causes ocean tides on earth. How does centrifugal force cause the far-side bulge? | The tidal bulge on the far side of the earth is not caused by centrifugal force. It is caused by the exact same thing the near-side bulge is caused by: the moon's gravity. Furthermore, tidal effects are not caused by the overall strength of gravity like planetary orbits are. Rather, tidal effects are instead caused by... | tag/gravity/ | context: tag/gravity/ question: I know that the gravity of the moon causes ocean tides on earth. How does centrifugal force cause the far-side bulge? | The tidal bulge on the far side of the earth is not caused by centrifugal force. It is caused by the exact same thing the near-side bulge is caused by: the moon's gravity. Furthermore, tidal effects are not caused by the overall strength of gravity like planetary orbits are. Rather, tidal effects are instead caused by... |
Is Pluto a planet? | It depends on how you define the word "planet". Science is fundamentally all about numbers and equations. Words are used in science almost grudgingly in order to communicate. The reason that numbers trump words in science is that numbers can be exact and universal while words are always culture-dependent and evolving ... | tag/gravity/ | context: tag/gravity/ question: Is Pluto a planet? | It depends on how you define the word "planet". Science is fundamentally all about numbers and equations. Words are used in science almost grudgingly in order to communicate. The reason that numbers trump words in science is that numbers can be exact and universal while words are always culture-dependent and evolving ... |
What is the speed of gravity? | The earth is held in its orbit about the sun by the sun's gravity. What if the sun suddenly disappeared, along with its light and gravity? As should be obvious, the earth would go dark and would slingshot out of the solar system. But when would the earth stop feeling the sun's gravity and tumble out of its orbit? Woul... | tag/gravity/ | context: tag/gravity/ question: What is the speed of gravity? | The earth is held in its orbit about the sun by the sun's gravity. What if the sun suddenly disappeared, along with its light and gravity? As should be obvious, the earth would go dark and would slingshot out of the solar system. But when would the earth stop feeling the sun's gravity and tumble out of its orbit? Woul... |
What keeps a bicycle balanced? | At first thought, you may think that the human rider is what keeps a bicycle balanced. This ends up not being completely true. If launched properly, a modern bike with no rider balances itself just fine and continues on its path as if a rider were guiding it. This can be easily verified by anyone with a bike, and can ... | tag/gravity/ | context: tag/gravity/ question: What keeps a bicycle balanced? | At first thought, you may think that the human rider is what keeps a bicycle balanced. This ends up not being completely true. If launched properly, a modern bike with no rider balances itself just fine and continues on its path as if a rider were guiding it. This can be easily verified by anyone with a bike, and can ... |
What would happen if you fell into a hole that went through the center of the earth? | For the sake of the argument, let's assume you could dig a wide, perfectly straight hole directly down to the center of earth and out to the other side of earth. Further suppose the hole has a strong enough wall to keep it from collapsing or melting. What would happen if you fell into this hole? After falling about 0.... | tag/gravity/ | context: tag/gravity/ question: What would happen if you fell into a hole that went through the center of the earth? | For the sake of the argument, let's assume you could dig a wide, perfectly straight hole directly down to the center of earth and out to the other side of earth. Further suppose the hole has a strong enough wall to keep it from collapsing or melting. What would happen if you fell into this hole? After falling about 0.... |
Why are all the stars fixed in space? | The stars are not fixed, but are constantly moving. If you factor out the daily arcing motion of the stars across the sky due to the earth's rotation, you end up with a pattern of stars that seems to never change. The stars seem so fixed that ancient sky-gazers mentally connected the stars into figures (constellations... | tag/gravity/ | context: tag/gravity/ question: Why are all the stars fixed in space? | The stars are not fixed, but are constantly moving. If you factor out the daily arcing motion of the stars across the sky due to the earth's rotation, you end up with a pattern of stars that seems to never change. The stars seem so fixed that ancient sky-gazers mentally connected the stars into figures (constellations... |
Why did people believe the earth is the center of the solar system when it's obvious the sun is? | The sun is not the center of the solar system. The center of our solar system is a point in space called the barycenter. The barycenter is very close to the sun, so calling the sun the center of the solar system is a reasonable approximation. But if you are going to do exact calculations, you have to use the barycente... | tag/gravity/ | context: tag/gravity/ question: Why did people believe the earth is the center of the solar system when it's obvious the sun is? | The sun is not the center of the solar system. The center of our solar system is a point in space called the barycenter. The barycenter is very close to the sun, so calling the sun the center of the solar system is a reasonable approximation. But if you are going to do exact calculations, you have to use the barycente... |
Why does the moon's gravity cause tides on earth but the sun's gravity doesn't? | The ocean tides on earth are caused by both the moon's gravity and the sun's gravity. In general, ocean tides are not generated by the overall strength of gravity, but instead by the differences in gravity from one spot to the next (the gravitational gradient). Even though the sun is much more massive and therefore ha... | tag/gravity/ | context: tag/gravity/ question: Why does the moon's gravity cause tides on earth but the sun's gravity doesn't? | The ocean tides on earth are caused by both the moon's gravity and the sun's gravity. In general, ocean tides are not generated by the overall strength of gravity, but instead by the differences in gravity from one spot to the next (the gravitational gradient). Even though the sun is much more massive and therefore ha... |
Why doesn't the earth fall down? | The earth does fall down. In fact, the earth is constantly falling down. It's a good thing too, because that is what keeps the earth from flying out of the solar system under its own momentum. Gravity is a centrally attractive force, meaning that objects in a gravitational field always fall towards the source of the g... | tag/gravity/ | context: tag/gravity/ question: Why doesn't the earth fall down? | The earth does fall down. In fact, the earth is constantly falling down. It's a good thing too, because that is what keeps the earth from flying out of the solar system under its own momentum. Gravity is a centrally attractive force, meaning that objects in a gravitational field always fall towards the source of the g... |
Why is gravity not a real force? | Gravity is indeed a real force, but not in the traditional sense. In other words, gravity is not a direct, classical, action-at-a-distance force between two objects. However, in the broader sense, gravity is indeed a force because it describes the resulting interaction between two masses. Gravitational effects are fun... | tag/gravity/ | context: tag/gravity/ question: Why is gravity not a real force? | Gravity is indeed a real force, but not in the traditional sense. In other words, gravity is not a direct, classical, action-at-a-distance force between two objects. However, in the broader sense, gravity is indeed a force because it describes the resulting interaction between two masses. Gravitational effects are fun... |
Why is physics scale invariant? | In general, physics is not scale invariant. There are a few reasons for this: 1. The universe is quantum on small scales. When an interaction field is quantized, it means that it is composed of a collection of fundamental units that can not be further subdivided. These units (quanta) have fixed properties. For instanc... | tag/gravity/ | context: tag/gravity/ question: Why is physics scale invariant? | In general, physics is not scale invariant. There are a few reasons for this: 1. The universe is quantum on small scales. When an interaction field is quantized, it means that it is composed of a collection of fundamental units that can not be further subdivided. These units (quanta) have fixed properties. For instanc... |
Why is there no gravity in space? | There is gravity in space – lots of it. Gravity is everywhere. It is true that as you get farther from the earth, its gravitational pull weakens. But it dies off quite slowly (compared to nuclear forces). And gravity never goes completely away. When you get very close to some other large body; the moon, Mars, or the s... | tag/gravity/ | context: tag/gravity/ question: Why is there no gravity in space? | There is gravity in space – lots of it. Gravity is everywhere. It is true that as you get farther from the earth, its gravitational pull weakens. But it dies off quite slowly (compared to nuclear forces). And gravity never goes completely away. When you get very close to some other large body; the moon, Mars, or the s... |
Why is there no up and down in space? | There is an up and down in space. "Down" is simply the direction gravity is pulling you, and "up" is just the opposite direction. Since there is gravity everywhere in space, there is also an up and down everywhere in space. Gravity is a centrally attractive force, so "going down" means falling or being pulled towards ... | tag/gravity/ | context: tag/gravity/ question: Why is there no up and down in space? | There is an up and down in space. "Down" is simply the direction gravity is pulling you, and "up" is just the opposite direction. Since there is gravity everywhere in space, there is also an up and down everywhere in space. Gravity is a centrally attractive force, so "going down" means falling or being pulled towards ... |
Will the night sky eventually end up completely black because the universe is expanding? | No, the night sky will not eventually end up completely black. It is true that the universe is expanding, which causes many stars to be farther and farther away from earth, and therefore causes them to be dimmer. But the expansion of the universe only affects the distance between galaxy groups. It does not affect the ... | tag/gravity/ | context: tag/gravity/ question: Will the night sky eventually end up completely black because the universe is expanding? | No, the night sky will not eventually end up completely black. It is true that the universe is expanding, which causes many stars to be farther and farther away from earth, and therefore causes them to be dimmer. But the expansion of the universe only affects the distance between galaxy groups. It does not affect the ... |
Would a guitar sound the same on a space station? | Yes. Since a space station typically contains regular air at normal pressure in order to keep the humans comfortable, the sounds created by playing a guitar will be the same as on earth. The weightless environment inside a space station has no effect on the guitar's ability to create sound. Sound is created by the str... | tag/gravity/ | context: tag/gravity/ question: Would a guitar sound the same on a space station? | Yes. Since a space station typically contains regular air at normal pressure in order to keep the humans comfortable, the sounds created by playing a guitar will be the same as on earth. The weightless environment inside a space station has no effect on the guitar's ability to create sound. Sound is created by the str... |
How does a microwave oven heat up food even though it emits no thermal radiation? | A microwave oven does emit thermal radiation to heat up food. Microwave radiation is thermal radiation. For some reason, pre-college teachers and books have a mistaken notion that thermal radiation = infrared radiation. All frequencies of the electromagnetic spectrum carry energy, from radio waves, microwaves, infrare... | tag/heat/ | context: tag/heat/ question: How does a microwave oven heat up food even though it emits no thermal radiation? | A microwave oven does emit thermal radiation to heat up food. Microwave radiation is thermal radiation. For some reason, pre-college teachers and books have a mistaken notion that thermal radiation = infrared radiation. All frequencies of the electromagnetic spectrum carry energy, from radio waves, microwaves, infrare... |
Is metal a good heat shield? | If used in a certain way, metal can indeed act as a good heat shield. At the same time, if metal is used in a different way, it can act as a good heat sink, which is the opposite of a heat shield. There are three ways that heat can be transported from one place to another: through radiation, through conduction, and th... | tag/heat/ | context: tag/heat/ question: Is metal a good heat shield? | If used in a certain way, metal can indeed act as a good heat shield. At the same time, if metal is used in a different way, it can act as a good heat sink, which is the opposite of a heat shield. There are three ways that heat can be transported from one place to another: through radiation, through conduction, and th... |
What keeps the continents floating on a sea of molten rock? | The continents do not float on a sea of molten rock. The continental and oceanic crusts sit on a thick layer of solid rock known as the mantle. While there is a layer of liquid rock in the earth known as the outer core, this layer is about 3000 km below earth's surface and is separated from the surface by the thick so... | tag/heat/ | context: tag/heat/ question: What keeps the continents floating on a sea of molten rock? | The continents do not float on a sea of molten rock. The continental and oceanic crusts sit on a thick layer of solid rock known as the mantle. While there is a layer of liquid rock in the earth known as the outer core, this layer is about 3000 km below earth's surface and is separated from the surface by the thick so... |
What makes meteorites so hot that you can't touch them? | Meteorites – the rocks from space that land on earth – are cold compared to typical earth temperatures. The reason for this is that they have just come from deep space, which is cold. It is true that when a meteorite falls through the atmosphere, the air shock heats the outer surface until it is vaporized. But there i... | tag/heat/ | context: tag/heat/ question: What makes meteorites so hot that you can't touch them? | Meteorites – the rocks from space that land on earth – are cold compared to typical earth temperatures. The reason for this is that they have just come from deep space, which is cold. It is true that when a meteorite falls through the atmosphere, the air shock heats the outer surface until it is vaporized. But there i... |
When hang-drying clothes, which is faster, indoors or outdoors? | The answer to this question really depends on your situation. Let us state the question more concretely: we have a clean, wet load of laundry that just got washed. We want to dry the clothes as quickly as possible but only have the option of hanging up the clothes to dry. Would it be quicker to dry the clothes by hang... | tag/heat/ | context: tag/heat/ question: When hang-drying clothes, which is faster, indoors or outdoors? | The answer to this question really depends on your situation. Let us state the question more concretely: we have a clean, wet load of laundry that just got washed. We want to dry the clothes as quickly as possible but only have the option of hanging up the clothes to dry. Would it be quicker to dry the clothes by hang... |
Why can you boil a frog without it jumping out to safety if you raise the temperature slowly? | No matter how slowly you raise the temperature, a frog will attempt to jump to safety when it becomes uncomfortably hot. (If the water is already boiling when you throw the frog in, he will die before he has a chance to jump.) According to the business magazine "Fast Company", which interviewed several scientists and ... | tag/heat/ | context: tag/heat/ question: Why can you boil a frog without it jumping out to safety if you raise the temperature slowly? | No matter how slowly you raise the temperature, a frog will attempt to jump to safety when it becomes uncomfortably hot. (If the water is already boiling when you throw the frog in, he will die before he has a chance to jump.) According to the business magazine "Fast Company", which interviewed several scientists and ... |
Why does the coldest time of the year align with the darkest time of the year? | In general, the coldest time of the year does not align with the darkest time of the year. The basic reason for this discrepancy is the fact that objects take time to cool down and heat up. The earth rotates daily about its rotational axis, which is an imaginary line connecting the North and South geographic poles. In... | tag/heat/ | context: tag/heat/ question: Why does the coldest time of the year align with the darkest time of the year? | In general, the coldest time of the year does not align with the darkest time of the year. The basic reason for this discrepancy is the fact that objects take time to cool down and heat up. The earth rotates daily about its rotational axis, which is an imaginary line connecting the North and South geographic poles. In... |
Does licorice cause high blood pressure? | Yes. Consumption of licorice (liquorice) can lead to dangerously high blood pressure and dangerously low potassium levels (hypokalemia). Licorice contains glycyrrhizinic acid, which sets off a well-understood chain reaction of biochemical events in the body resulting in high blood pressure. In a healthy person, the ki... | tag/high-blood-pressure/ | context: tag/high-blood-pressure/ question: Does licorice cause high blood pressure? | Yes. Consumption of licorice (liquorice) can lead to dangerously high blood pressure and dangerously low potassium levels (hypokalemia). Licorice contains glycyrrhizinic acid, which sets off a well-understood chain reaction of biochemical events in the body resulting in high blood pressure. In a healthy person, the ki... |
As light from a star spreads out and weakens, do gaps form between the photons? | The answer depends on how you look at light. However, in the most accurate approach, gaps do not form between photons as light spreads out. Light is made up of tiny fundamental bits called photons. A photon is a quantum object. As such, a photon acts a little like a particle and a little like a wave, but is actually s... | tag/light/ | context: tag/light/ question: As light from a star spreads out and weakens, do gaps form between the photons? | The answer depends on how you look at light. However, in the most accurate approach, gaps do not form between photons as light spreads out. Light is made up of tiny fundamental bits called photons. A photon is a quantum object. As such, a photon acts a little like a particle and a little like a wave, but is actually s... |
Can air make shadows? | Yes, air can indeed make shadows. A shadow occurs when an object in a light beam prevents some of the light from continuing on in the forward direction. When the light beam hits a wall or the ground, a darker shape is visible where less light is hitting the surface. Both the light and the shadow, which is just the abs... | tag/light/ | context: tag/light/ question: Can air make shadows? | Yes, air can indeed make shadows. A shadow occurs when an object in a light beam prevents some of the light from continuing on in the forward direction. When the light beam hits a wall or the ground, a darker shape is visible where less light is hitting the surface. Both the light and the shadow, which is just the abs... |
Can light bend around corners? | Yes, light can bend around corners. In fact, light always bends around corners to some extent. This is a basic property of light and all other waves. The amount of light that bends around a corner depends on the exact situation. For visible light on the human scale, the amount of light that bends around corners is oft... | tag/light/ | context: tag/light/ question: Can light bend around corners? | Yes, light can bend around corners. In fact, light always bends around corners to some extent. This is a basic property of light and all other waves. The amount of light that bends around a corner depends on the exact situation. For visible light on the human scale, the amount of light that bends around corners is oft... |
Can radio antennas emit visible light? | Yes, radio antennas can emit visible light, but probably not in the way that you're thinking. If you pump enough energy into a radio antenna, you can heat it up until it glows and emits visible light through the process of thermal radiation. However, a regular radio antenna cannot emit visible light that carries infor... | tag/light/ | context: tag/light/ question: Can radio antennas emit visible light? | Yes, radio antennas can emit visible light, but probably not in the way that you're thinking. If you pump enough energy into a radio antenna, you can heat it up until it glows and emits visible light through the process of thermal radiation. However, a regular radio antenna cannot emit visible light that carries infor... |
Can you make a shock wave of light by breaking the light barrier just like supersonic airplanes break the sound barrier? | Yes and no. It depends on the material you are in. In order to keep things from traveling into the past, and thereby preserve local conservation of mass-energy, and thereby prohibit the universe from exploding in an instant, nothing can travel faster than the speed of light in vacuum. Supersonic airplanes break the so... | tag/light/ | context: tag/light/ question: Can you make a shock wave of light by breaking the light barrier just like supersonic airplanes break the sound barrier? | Yes and no. It depends on the material you are in. In order to keep things from traveling into the past, and thereby preserve local conservation of mass-energy, and thereby prohibit the universe from exploding in an instant, nothing can travel faster than the speed of light in vacuum. Supersonic airplanes break the so... |
Do humans give off radiation? | Yes, humans give off radiation. Humans give off mostly infrared radiation, which is electromagnetic radiation with a frequency lower than visible light. This effect is not unique to humans. All objects with a non-zero temperature give off thermal radiation. And because a temperature of exactly absolute zero is physica... | tag/light/ | context: tag/light/ question: Do humans give off radiation? | Yes, humans give off radiation. Humans give off mostly infrared radiation, which is electromagnetic radiation with a frequency lower than visible light. This effect is not unique to humans. All objects with a non-zero temperature give off thermal radiation. And because a temperature of exactly absolute zero is physica... |
How bright is a laser beam when viewed from the side? | While traveling through the vacuum of space, laser beams are invisible unless shot directly into your eye. The experience you know of as vision consists of light entering your eyes and being detecting by cells on your retinas. You can't see any light that never enters your eyes. A beam of light, including laser light,... | tag/light/ | context: tag/light/ question: How bright is a laser beam when viewed from the side? | While traveling through the vacuum of space, laser beams are invisible unless shot directly into your eye. The experience you know of as vision consists of light entering your eyes and being detecting by cells on your retinas. You can't see any light that never enters your eyes. A beam of light, including laser light,... |
How can a clear object be transparent and visible at the same time? | Clear objects are visible because they bend the light as it passes through. There are four basic things that can happen to light when it hits an object: In reality, all materials interact with light in all four ways. For instance, consider the hood of a red sports car. Some of the light is reflected specularly (leadin... | tag/light/ | context: tag/light/ question: How can a clear object be transparent and visible at the same time? | Clear objects are visible because they bend the light as it passes through. There are four basic things that can happen to light when it hits an object: In reality, all materials interact with light in all four ways. For instance, consider the hood of a red sports car. Some of the light is reflected specularly (leadin... |
How did Archimedes use mirrors to burn up invaders' ships? | Archimedes did not use mirrors to burn up the Roman invaders' ships. This myth claims that by focusing the sun's rays, Archimedes' mirrors raised the temperature of the ships enough that they caught fire. While a concave mirror held in one hand can light a paper in the other hand by focusing sunlight, burning a distan... | tag/light/ | context: tag/light/ question: How did Archimedes use mirrors to burn up invaders' ships? | Archimedes did not use mirrors to burn up the Roman invaders' ships. This myth claims that by focusing the sun's rays, Archimedes' mirrors raised the temperature of the ships enough that they caught fire. While a concave mirror held in one hand can light a paper in the other hand by focusing sunlight, burning a distan... |
How do space ships fly faster than light? | Nothing can travel faster than light. This is not a question of technology, but of fundamental physics. Special relativity tells us that nothing can travel faster than the speed of light in vacuum (671 million mph or 300 million meters per second). This limitation applies to baseballs, protons, space ships, and cell p... | tag/light/ | context: tag/light/ question: How do space ships fly faster than light? | Nothing can travel faster than light. This is not a question of technology, but of fundamental physics. Special relativity tells us that nothing can travel faster than the speed of light in vacuum (671 million mph or 300 million meters per second). This limitation applies to baseballs, protons, space ships, and cell p... |
How do you make a one-photon-thick beam of light? | There is no such thing as a one-photon-thick beam of light. Photons are not solid little balls that can be lined up in a perfectly straight beam that is one photon wide. Instead, photons are quantum objects. As such, photons act somewhat like waves and somewhat like particles at the same time. When traveling through f... | tag/light/ | context: tag/light/ question: How do you make a one-photon-thick beam of light? | There is no such thing as a one-photon-thick beam of light. Photons are not solid little balls that can be lined up in a perfectly straight beam that is one photon wide. Instead, photons are quantum objects. As such, photons act somewhat like waves and somewhat like particles at the same time. When traveling through f... |
How does a photon accelerate to light speed so quickly? | A photon of light does not accelerate to light speed. Rather, a photon is already traveling at light speed c when it is created. It's not like a photon jumps from a speed of zero to light speed instantaneously. Rather, a photon is always traveling at c, from the moment of its creation. If you think of a photon as a so... | tag/light/ | context: tag/light/ question: How does a photon accelerate to light speed so quickly? | A photon of light does not accelerate to light speed. Rather, a photon is already traveling at light speed c when it is created. It's not like a photon jumps from a speed of zero to light speed instantaneously. Rather, a photon is always traveling at c, from the moment of its creation. If you think of a photon as a so... |
How does diffraction make a tree's shadow blurry? | Diffraction is not what makes a tree's shadow blurry. The shadows of trees, buildings, and other outdoor objects are made blurry by the fact that the sun is an extended light source. Although diffraction can make shadows blurry, for human-sized objects at visible wavelengths of light, the diffraction of light is small... | tag/light/ | context: tag/light/ question: How does diffraction make a tree's shadow blurry? | Diffraction is not what makes a tree's shadow blurry. The shadows of trees, buildings, and other outdoor objects are made blurry by the fact that the sun is an extended light source. Although diffraction can make shadows blurry, for human-sized objects at visible wavelengths of light, the diffraction of light is small... |
How does looking at distant galaxies allow us to look back in time? | Strictly speaking, when telescopes look at the light from distant galaxies, they are not literally looking back in time. The past no longer exists, so no one can directly look at it. Instead, the telescopes are looking at the present-time pattern of a beam of light. Since the beam of light has been traveling through t... | tag/light/ | context: tag/light/ question: How does looking at distant galaxies allow us to look back in time? | Strictly speaking, when telescopes look at the light from distant galaxies, they are not literally looking back in time. The past no longer exists, so no one can directly look at it. Instead, the telescopes are looking at the present-time pattern of a beam of light. Since the beam of light has been traveling through t... |
Is light a particle or a wave? | In an approximate way, light is both a particle and a wave. But in an exact representation, light is neither a particle nor a wave, but is something more complex. As a metaphor, consider a cylindrical can of beans. If you hold the can sideways, force a friend to only look at its shadow, and ask him what shape the obje... | tag/light/ | context: tag/light/ question: Is light a particle or a wave? | In an approximate way, light is both a particle and a wave. But in an exact representation, light is neither a particle nor a wave, but is something more complex. As a metaphor, consider a cylindrical can of beans. If you hold the can sideways, force a friend to only look at its shadow, and ask him what shape the obje... |
Is the reason that nothing can go faster than light because we have not tried hard enough? | No. The universal speed limit, which we commonly call the speed of light, is fundamental to the way the universe works. It is difficult to visualize this if you have never heard about it before, but scientists have found that the faster you go, the more your spatial dimension in the forward direction shrinks and the s... | tag/light/ | context: tag/light/ question: Is the reason that nothing can go faster than light because we have not tried hard enough? | No. The universal speed limit, which we commonly call the speed of light, is fundamental to the way the universe works. It is difficult to visualize this if you have never heard about it before, but scientists have found that the faster you go, the more your spatial dimension in the forward direction shrinks and the s... |
Since a star's light takes so long to reach us, how do we know that the star is still there? | We don't know that it is still there. For all we know, the North Star or any other star could have been ingested by a passing black hole years ago. (Although this is highly unlikely, it is possible.) When you look at a star, you are looking at the light that came from the star. Because stars are so far away, it takes ... | tag/light/ | context: tag/light/ question: Since a star's light takes so long to reach us, how do we know that the star is still there? | We don't know that it is still there. For all we know, the North Star or any other star could have been ingested by a passing black hole years ago. (Although this is highly unlikely, it is possible.) When you look at a star, you are looking at the light that came from the star. Because stars are so far away, it takes ... |
What is the speed of dark? | Darkness travels at the speed of light. More accurately, darkness does not exist by itself as a unique physical entity, but is simply the absence of light. Any time you block out most of the light – for instance, by cupping your hands together – you get darkness. In the context of talking about speeds, darkness is wha... | tag/light/ | context: tag/light/ question: What is the speed of dark? | Darkness travels at the speed of light. More accurately, darkness does not exist by itself as a unique physical entity, but is simply the absence of light. Any time you block out most of the light – for instance, by cupping your hands together – you get darkness. In the context of talking about speeds, darkness is wha... |
What makes a "fluorescent" highlighter marker so bright? | Fluorescent highlighter markers are so bright because they are literally fluorescent. When used to describe highlighters, the word "fluorescent" is not a vague term that means "extra bright". Rather, this word is an exact, scientific term indicating that the highlighter ink exhibits fluorescence. Fluorescence is the p... | tag/light/ | context: tag/light/ question: What makes a "fluorescent" highlighter marker so bright? | Fluorescent highlighter markers are so bright because they are literally fluorescent. When used to describe highlighters, the word "fluorescent" is not a vague term that means "extra bright". Rather, this word is an exact, scientific term indicating that the highlighter ink exhibits fluorescence. Fluorescence is the p... |
What makes the light waves in laser light parallel? | The waves in laser light are not parallel. It is theoretically impossible to construct a beam with perfectly parallel rays unless you have an infinitely wide beam. As described in the textbook "Principles of Lasers" by Orazio Svelto, even a perfectly spatially coherent beam will spread out due to diffraction. Diffract... | tag/light/ | context: tag/light/ question: What makes the light waves in laser light parallel? | The waves in laser light are not parallel. It is theoretically impossible to construct a beam with perfectly parallel rays unless you have an infinitely wide beam. As described in the textbook "Principles of Lasers" by Orazio Svelto, even a perfectly spatially coherent beam will spread out due to diffraction. Diffract... |
What would happen if you drove your car close to the speed of light and turned on the headlights? | Light in vacuum always travels at the same speed c, exactly 299,792,458 meters per second, no matter how it is created or in what frame it is observed. If you drove a car close to the speed of light relative to the ground (neglect air effects) and turn on the headlights, light would leave your headlights at speed c th... | tag/light/ | context: tag/light/ question: What would happen if you drove your car close to the speed of light and turned on the headlights? | Light in vacuum always travels at the same speed c, exactly 299,792,458 meters per second, no matter how it is created or in what frame it is observed. If you drove a car close to the speed of light relative to the ground (neglect air effects) and turn on the headlights, light would leave your headlights at speed c th... |
When does a light beam have only a single frequency? | A light beam never has exactly one frequency. Even a single bit of light (a photon) never has exactly one frequency. It is fundamentally impossible for a photon to have exactly one frequency. Certain beams of light, such as laser beams, can get very close to having one frequency, but can never have exactly one frequen... | tag/light/ | context: tag/light/ question: When does a light beam have only a single frequency? | A light beam never has exactly one frequency. Even a single bit of light (a photon) never has exactly one frequency. It is fundamentally impossible for a photon to have exactly one frequency. Certain beams of light, such as laser beams, can get very close to having one frequency, but can never have exactly one frequen... |
When I bump one end of a long metal bar, the other end instantaneously moves. Can I use this to send messages faster than light? | When you bump one end of a long metal bar, the other end does not instantaneously move. The movement would be instantaneous if the bar were perfectly rigid, but perfectly rigid materials are fundamentally impossible in the real world. Although the movement of the bar may seem uniform and instantaneous to our human eye... | tag/light/ | context: tag/light/ question: When I bump one end of a long metal bar, the other end instantaneously moves. Can I use this to send messages faster than light? | When you bump one end of a long metal bar, the other end does not instantaneously move. The movement would be instantaneous if the bar were perfectly rigid, but perfectly rigid materials are fundamentally impossible in the real world. Although the movement of the bar may seem uniform and instantaneous to our human eye... |
Why can't flat lenses focus light? | Actually, flat lenses can focus light if they are built properly. Let us look at the basics of lenses and then at different types of flat lenses. A traditional lens is essentially a curved piece of glass that bends light through a process known as "refraction". Whenever a ray of light travels from one transparent mate... | tag/light/ | context: tag/light/ question: Why can't flat lenses focus light? | Actually, flat lenses can focus light if they are built properly. Let us look at the basics of lenses and then at different types of flat lenses. A traditional lens is essentially a curved piece of glass that bends light through a process known as "refraction". Whenever a ray of light travels from one transparent mate... |
Why do camera flashes make your eyes turn red? | Camera flashes do not make your eyes turn red. The inside of your eyes are always red. The bright light of the camera flash just makes the color more obvious. Your eye is essentially a hollow ball filled with clear fluid. The hole at the front of your eye, the pupil, lets light into the hollow space inside the eye. Th... | tag/light/ | context: tag/light/ question: Why do camera flashes make your eyes turn red? | Camera flashes do not make your eyes turn red. The inside of your eyes are always red. The bright light of the camera flash just makes the color more obvious. Your eye is essentially a hollow ball filled with clear fluid. The hole at the front of your eye, the pupil, lets light into the hollow space inside the eye. Th... |
Why do mirrors flip left to right and not up to down? | Mirrors do not flip left to right. They flip front to back. Mirrors reflect light rays such that the angle of reflection equals the angle of incidence. For a three-dimensional object standing in front of the mirror, there is an image of the object created behind the mirror with the right side still on the right, the l... | tag/light/ | context: tag/light/ question: Why do mirrors flip left to right and not up to down? | Mirrors do not flip left to right. They flip front to back. Mirrors reflect light rays such that the angle of reflection equals the angle of incidence. For a three-dimensional object standing in front of the mirror, there is an image of the object created behind the mirror with the right side still on the right, the l... |
Why does my room get dark when I turn the lights off even if my window is shut? | Light does not go away by leaking out through doors and windows. Light goes away by being quickly absorbed by materials and converted to heat and other forms of energy. In contrast to wind or smoke, light has no mass and is not composed of atoms. Because of this, light travels quickly in straight lines until it hits a... | tag/light/ | context: tag/light/ question: Why does my room get dark when I turn the lights off even if my window is shut? | Light does not go away by leaking out through doors and windows. Light goes away by being quickly absorbed by materials and converted to heat and other forms of energy. In contrast to wind or smoke, light has no mass and is not composed of atoms. Because of this, light travels quickly in straight lines until it hits a... |
Why is the moon so bright? | The moon is actually quite dim, compared to other astronomical bodies. The moon only seems bright in the night sky because it is so close to the earth and because the trees, houses, and fields around you are so dark at night. In fact, the moon is one of the least reflective objects in the solar system. The DSCOVER spa... | tag/light/ | context: tag/light/ question: Why is the moon so bright? | The moon is actually quite dim, compared to other astronomical bodies. The moon only seems bright in the night sky because it is so close to the earth and because the trees, houses, and fields around you are so dark at night. In fact, the moon is one of the least reflective objects in the solar system. The DSCOVER spa... |
Why is the sun cold in the winter? | The sun does not get cold in the winter. The sun is a giant ball of fire driven by nuclear reactions. The surface of the sun stays at an incredibly hot temperature of about 5800 Kelvin all year long. The high temperature of the sun causes it to constantly emit prodigious amounts of thermal radiation in all directions,... | tag/light/ | context: tag/light/ question: Why is the sun cold in the winter? | The sun does not get cold in the winter. The sun is a giant ball of fire driven by nuclear reactions. The surface of the sun stays at an incredibly hot temperature of about 5800 Kelvin all year long. The high temperature of the sun causes it to constantly emit prodigious amounts of thermal radiation in all directions,... |
Why is time frozen from light's perspective? | Time is not frozen from light's perspective, because light does not have a perspective. There is no valid reference frame in which light is at rest. This statement is not a minor issue that can be approximated away or overcome by a different choice of words. This statement is fundamental to Einstein's theory of Specia... | tag/light/ | context: tag/light/ question: Why is time frozen from light's perspective? | Time is not frozen from light's perspective, because light does not have a perspective. There is no valid reference frame in which light is at rest. This statement is not a minor issue that can be approximated away or overcome by a different choice of words. This statement is fundamental to Einstein's theory of Specia... |
Why are all metals magnetic? | Not all metals are magnetic. Actually, it depends on what you mean by the word "magnetic". There are four basic types of magnetism that a material can have: superconducting, diamagnetic, paramagnetic, and lastly ferromagnetic. Superconducting materials are strongly repelled from permanent magnets. Diamagnetic material... | tag/magnetism/ | context: tag/magnetism/ question: Why are all metals magnetic? | Not all metals are magnetic. Actually, it depends on what you mean by the word "magnetic". There are four basic types of magnetism that a material can have: superconducting, diamagnetic, paramagnetic, and lastly ferromagnetic. Superconducting materials are strongly repelled from permanent magnets. Diamagnetic material... |
Why does a magnetic compass point to the Geographic North Pole? | A magnetic compass does not point to the geographic north pole. A magnetic compass points to the earth's magnetic poles, which are not the same as earth's geographic poles. Furthermore, the magnetic pole near earth's geographic north pole is actually the south magnetic pole. When it comes to magnets, opposites attract... | tag/magnetism/ | context: tag/magnetism/ question: Why does a magnetic compass point to the Geographic North Pole? | A magnetic compass does not point to the geographic north pole. A magnetic compass points to the earth's magnetic poles, which are not the same as earth's geographic poles. Furthermore, the magnetic pole near earth's geographic north pole is actually the south magnetic pole. When it comes to magnets, opposites attract... |
Why don't galaxies have a natural magnetic field like the earth does? | Each galaxy does have a natural magnetic field, but it is weak. The magnetic field of our galaxy is about 100 times weaker than the magnetic field of the earth. The magnetic field of a galaxy has two basic components: a large-scale ordered pattern that mimics the shape of the galaxy, and a small-scale random pattern. ... | tag/magnetism/ | context: tag/magnetism/ question: Why don't galaxies have a natural magnetic field like the earth does? | Each galaxy does have a natural magnetic field, but it is weak. The magnetic field of our galaxy is about 100 times weaker than the magnetic field of the earth. The magnetic field of a galaxy has two basic components: a large-scale ordered pattern that mimics the shape of the galaxy, and a small-scale random pattern. ... |
How can you cancel out the jolt of a quick start? | Acceleration always creates inertial forces. When you slam on your car's gas pedal, the rapid acceleration throws you back into your seat. The force you feel pushing you back is called an "inertial force". Every time a frame of reference is accelerated, objects in that frame of reference experience an inertial force. ... | tag/mass/ | context: tag/mass/ question: How can you cancel out the jolt of a quick start? | Acceleration always creates inertial forces. When you slam on your car's gas pedal, the rapid acceleration throws you back into your seat. The force you feel pushing you back is called an "inertial force". Every time a frame of reference is accelerated, objects in that frame of reference experience an inertial force. ... |
How does a penny left on the track derail a train? | A penny left on a track does not typically derail a train. A train speeding along its track is a very heavy object with an immense amount of momentum. The penny is simply too light to do much of anything. It is flattened or knocked out of the way by the train. The basic principle at work is the conservation of momentu... | tag/momentum/ | context: tag/momentum/ question: How does a penny left on the track derail a train? | A penny left on a track does not typically derail a train. A train speeding along its track is a very heavy object with an immense amount of momentum. The penny is simply too light to do much of anything. It is flattened or knocked out of the way by the train. The basic principle at work is the conservation of momentu... |
What is the range of weapons if used in space? | Weapons in space would have an effectively infinite range. On earth, gravity inevitably slams bullets, missiles, rockets, mortars, and bombs into the ground. As a result, every weapon has a characteristic range limit beyond which it can not reach. In outer space, there is still gravity, but an object is so far away fr... | tag/momentum/ | context: tag/momentum/ question: What is the range of weapons if used in space? | Weapons in space would have an effectively infinite range. On earth, gravity inevitably slams bullets, missiles, rockets, mortars, and bombs into the ground. As a result, every weapon has a characteristic range limit beyond which it can not reach. In outer space, there is still gravity, but an object is so far away fr... |
What makes guns so dangerous? | The momentum imparted to the bullet by the gun is what makes a gun able to do so much damage. The momentum of an object equals its mass times its velocity. The momentum of an object, and therefore its ability to cause destruction, can be increased by making the object more massive or by making it go faster. Although t... | tag/momentum/ | context: tag/momentum/ question: What makes guns so dangerous? | The momentum imparted to the bullet by the gun is what makes a gun able to do so much damage. The momentum of an object equals its mass times its velocity. The momentum of an object, and therefore its ability to cause destruction, can be increased by making the object more massive or by making it go faster. Although t... |
How can astronomers know things for certain since they only look at space from one vantage point? | Astronomers do not look at space objects from only one vantage point. You may think that since we are stuck on earth looking out towards space, we can only see space objects from a single viewing angle, and therefore our knowledge is limited. For instance, you may think that perhaps there is an alien city on the far s... | tag/moon/ | context: tag/moon/ question: How can astronomers know things for certain since they only look at space from one vantage point? | Astronomers do not look at space objects from only one vantage point. You may think that since we are stuck on earth looking out towards space, we can only see space objects from a single viewing angle, and therefore our knowledge is limited. For instance, you may think that perhaps there is an alien city on the far s... |
What is it about a full moon that makes people do crazy things and commit crimes? | There are no statistically significant records indicating any connection between crime waves or full hospitals and the full moon, according to the National Geographic News. This misunderstanding perhaps has its source in a long line of mythology. Werewolves were said to be humans that turned into wolves during the ful... | tag/moon/ | context: tag/moon/ question: What is it about a full moon that makes people do crazy things and commit crimes? | There are no statistically significant records indicating any connection between crime waves or full hospitals and the full moon, according to the National Geographic News. This misunderstanding perhaps has its source in a long line of mythology. Werewolves were said to be humans that turned into wolves during the ful... |
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