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time 7!,- T, /., - Lv That is, 44 MECHANICS L2- Ll = 9l(Tt - 7\) + | a(T2 - r,)2, or ^•=^i + «i(r,-r1)+Ja(r,-rl)^. (2) (If the acceleration is an opposite sense to the speed, a must be given a negative value.) Thus, if the acceleration is known, and if the position and speed at any one instant are given, they can be p... |
M(AOP) or B'- N). This, therefore, equals - 52 MW11AXIC8 Rotation As already stated, the name "rotation" is given the motion of a geometrical figure when, at any instant, each point of the figure moves in a circle ; the planes of these circles are all parallel, and their centres lie on a line called the "axis." It was ... |
at any instant, i.e. the rate at which Q passes along the arc of its circle, equals the product of r by the value of the angular speed of that instant, i.e. the rate at which the radius describes the angle. To return to the idea of angular velocity, it is evident that it can be represented by a rotor ; and since an an... |
spinning top whose axis is not vertical, a rolling hoop turn- ing a corner, etc. In the general case, of course, both the angular speed and the direction of the axis change. In tin- case of rotation around a fixed axis there is evidently a simple connection between the angular acceleration and the linear acceleration ... |
LMir-'. the tliiv. \\hosr a\i> of rotation is changing. Angular speed is altered 1 < 1 i i ig an angular velocity around the same a Tin- diivrti-.n,,f il i. 1 1)\ adding a relocitj in altered 1»\ ad.lii: ;ular a (litTt-rrnt velocity around a dill-. tlir two IvillLT ill tll«' CHAPTER II DYNAMICS Introduction. — In descr... |
production of the force. Similarly, if two moving bodies strike each other, the motion of each is changed ; so each exerts a force on the other. We cannot directly investigate the motion of molecules, nor can we understand or even describe the action between the falling body and the earth, partly owing to the great si... |
, but in opposite directions, and that the ratio of these accelerations is a constant quantity. We can, therefore, assign a number to each body such that, if m^ and w2 are these numbers, and al and #2 are the accelerations, m^ = —m2a2. Similarly, if we have a third particle, we can assign a number to it by allowing it ... |
presently, the prop- erty of the centre of mass as just stated. One manner in which this comparison can be imagined done — although it is not practicable — is to place the two bodies on a smooth, horizontal table, so that gravity has no action and that the motion is not affected by friction ; and, attaching to each in... |
produce the sam. •. • • i tion as does the Standard body. Thus \\e obtain a Ml body of mass 1. Similarly, we can obtain a lx»d\ of mass 2 by first suspending together the two bodies of unit mats, noting the elongation, and then deterrninun: a third 1 which produces this same elongation ; etc. To obtain a 1 Fto. ». — S... |
explode into fragments ; it may be " electrified " or " magnetized " ; it may be melted if it is a solid, or* evaporated if it is a liquid, or vice versa. Simi- larly, if two pieces of matter are brought together, they may stick to each other like putty and glass ; or they may unite to produce new substances, like a p... |
.i M 67 C.G.S. System. — In all scientific work the units in terms of which lengths, intervals of time, and masses are expressed are the centimetre, the gram, and the mean solar second. This is called the "C.G.S. system." Force F= ma The Unit of Force. — The unit of force on this C. G. S. em is that which corresponds t... |
sum of several s. In |,,irti. -nlsr, if a = 0, /= 0 ; hut this does not mean necessarily that th«-re U n<» foroe; it may mean that there are two equal and opposite forces acting on the particle. 68 MECHANICS Thus, if a particle is suspended " at rest " at the end of a vertical wire, it has no acceleration, owing to th... |
spring does not change during the operations, we may thus obtain readings on a scale attached to the spring, which correspond to known forces. This process is called ** calibra- tion " of the spring. Then, to measure any force, we can observe how much it elongates the spring. (It -h to exert a known force in a definit... |
two types of acceleration, one when the speed changes and the direction does not, the other when the direction changes and the speed does not ; and correspond- ing to each of these is a definite type of force. In the one the force produces a change in speed ; in the other, a change in direction of motion. a. Rectiline... |
no com- ponent parallel to the plane, because it is perpendicular to it. The total FIG. 81.— Motion down a rough inclined plane..,..,,.,, force down the plane is, then, and so the acceleration is this divided by m ; i.e. mg sin N — F, mg sin N — F b. Centrifugal force. — In order to change the direction of motion of a... |
The force that is required to hold a particle in a circle \ aries dhvctly as its ma>s ; and. if the force applied i than " *~. the particle will move toward the centre. \\ hile, if it is less than this, the particle will move away from the centre. Therefore, if an emulsion of two liquids, one imnv dense than the othi ... |
called the "triangle of forces." This principle was first stated, for a special case, however, by Stevin, as early as 1G05. JFio.84. — Composition of Forcesj_ OA + OB= OC\_ Or, ~OA= OD+l>A ;_OB= OE +EB^_DA = - EB and OD=EC\ there- fore OA+OB=OC. The composition of forces is illustrated by the motion of a boat that is ... |
due to their interaction re- mains constant, so must the sum for all the particles; and, il sum of the total momenta of all the particles must ;. -main constant so long as there is no external act inn. This is called the " Principle of the Conservation of Linear Momentum." 80 MECHANICS Centre of Mass. — This principle... |
wz2«2 + "'» ^ *s ^ne sum °f tne compo- nents in this direction of all the forces, internal and external ; but the sum of the components of the internal forces is zero, and so only the sum of the components of the external forces need be considered. Call this sum X. Then m^a^m^a^ — equals X. We have just shown, however... |
the next Section. Illustrations of the calculation of the position of the centre of mass. It is easy to calculate the position of the centre of mass of any regular solid provided the matter is distributed uniformly throughout it, e.g. a cylindrical wire, a cube, a sphere, etc., and also of a system of bodies whose mas... |
=20; the dimen- sions and distances being as indicated ill the CUt. The centre of mass of the rod itself is its middle point ; which is at a dis- tance 15 cm. from the ends. Take as Fi«,..T.». Ontn-.if rn weighted bar. at its left of» the plane from which to measure « tances one perpemlieuhir to the rod Then m, = 15, r... |
expressly noted that this quantity has the same value wherever the point of application of the force is, provided only that the force keeps its line of action, i.e. provided I does not change. (Thus the force may be applied at Av or Av or Ay etc., in the line of action.) In discussing translation it was shown that the... |
is FIG. 46,-composition of the moments given by twice the area of the tri- of OB and OA about axis at P. -\ /-T-»/^r>x j 1-1 c /T7T i angle (POB), and that of OO by twice the area of the triangle (P0(7). But the area of the latter triangle equals the sum of the areas of the three tri- angles (POB), (PBC), and (6>£<7);... |
are worth noting, if the angular velocity of all the particles is the same, the angular moment um may be expressed (wjfj2 -f nyf + —)h\ and now, if o\viii«jf to any internal cause the values etc., become smaller, the value of h must increase. This \\;is the case with the planets in their early history and is s<> \\ith... |
rotation does not coincide with one of them there is a twist on the axle tending to make it turn. This push and twist must of course be withstood by the axle or its bearings. So, if the body is to turn freely, producing no forces or moments on the axle, the axis of rotation must pass through the centre of mass and mus... |
rotation will take place about it exactly as if it were a fixed point in the figure. Several illustrations have been given already ; viz., the motion of an acrobat, that of a chair thrown in the air, etc. If a rigid body is struck a blow at random, its centre of mass will move in the direction of the blow, and the bod... |
of the resultant is Fl + F^ if the forces are in the same direc- n tion; but, if they are opposite directions, and i is the greater, the resultant is in the direction of this force, and has the value F% — Fr Further, in order to satisfy the requirements in regard to rotation, this resultant must have such a position t... |
4- F Fto. tt.-Rlfftd body am). of two fttnUM fbTOM /', and value'l T *, where I is the perpendicular distan the centre of mass to the line of Action of the resultant, 100 and / is the moment of inertia about an axis through the centre of mass and perpendicular to the plane of the forces. This process may be continued ... |
centre of gravity " of the body ; and it is seen from the above equation that it coincides with the " centre of mass." N.B. — The above proof of the existence of a centre of gravity and of its coincidence with the centre of mass depends upon the fact that " g " is a constant for all amounts and all kinds of matter. Eq... |
?, there Is equilibrium. w for impulses in some din •< 'tions, it may be stable for others; and again a body may be stable for an extremely small impulse and unstable f..r a larger one, so that there are ••degrees of Stability." Thus a block shaped as shown in the rut and resting on a hori/.ontal support is in stable e... |
water, at a constant temperature is in stable equilibrium ; for if its temperature is suddenly increased in any way, the tendency will be for it to return to the tern- DYNAMICS 105 perature of the surrounding medium. Now, when the tem- perature of an iron bar is increased, its length is increased ; but this act of inc... |
names have been given its terms : \ ms2 is called the " kinetic energy " of the particle whose mass is m when its speed is s ; / (z2— x^) is called the " work done by the force " / in the distance x2 — xv provided the speed is increasing, or the " work done against the force " / if the speed is decreasing — thus this ... |
a lower parallel plane at a vertical distance A, the work done by gravity is mgh, and is independent of the path. This is a consequence of the fact that the force of gravity is vertical and is con- stant in amount at all points near the surface of the earth at any one locality. I)Y \AMICS 109 Potential Energy. — Since... |
have potential energy ; and, in gen- eral, a body or a system of bodies has potential energy if the particles composing it are in such a condition that a force is required to maintain it. The formula F(x% — x^) = F"t — F^ gives a means of cal- culating only the change in the potential energy ; and so what is meant by ... |
The exact relation between this gain and loss is stated in the general formula V+ \ m& = constant, which is true only for so-called "con- servative" forces. (See page 108.) This says that, if a tern has both kinetic and potential energies, the sum of the two remains constant; if one decreases, the other increases by a... |
common use ; it is called a " joule," in honor of the great English physicist who did so much to teach correct ideas in regard to energy. Another unit often used is the "foot pound," or the work required to raise in a vertical direction a distance of one foot a body whose mass is one pound. This, then, equals approxim... |
i.e. if Vl>Vy F is positive, and is, therefore, in the direction from point 1 to point 2 ; so there is a force acting in the direction of the displacement, whose value is — -. This is illustrated by 2*2 - X\ the force of gravity, that of a compressed spring, etc. Another interpretation is this : in a system left to it... |
pieces of matter in contact with each other move relatively: and in all the cases of motion i-sed the condit «'SSed as to assume the eomph-t.- lion. It is* a force 116 MECHANICS that always opposes the motion : and its numerical proper- ties will be discussed later. Let us consider several cases of friction and the im... |
, it describes a condition of a body with reference to other bodies or of the parts of a b»»dy witli ivtVivnce to each other, which is primarily concerned with the idea of force and its production. We cannot ex- plain it in terms of such simple quantities as intervals of •e or time and mass. We understand, however, its... |
friction opposing this, call its value F^\ then the total force producing the acceleration is (F — F^), and if m TTf TTf is the mass of the moving block, its acceleration is ^. m If there is no acceleration, and therefore the speed remains constant, the applied force exactly balances the friction, F = Fl ; and we have... |
parta of the machine is decreasing, they t! •* do 122 MECHANICS work in helping to overcome the opposing force. Therefore, in the discussion that follows, the effect of friction will be neg- lected; and we shall assume that there is no acceleration. Con- sequently, the energy furnished the machine equals the work it d... |
v i.e. or I'This relation also expresses the fact that the body is in equilibrium under the action of two forces whose values are I-\ and /-'2, and which are properly directed. Illustrations of the lever are given by a pump handle, a crowbar, a pair of scissors, a pair of tongs, nutcrackers, etc. The formula for a leve... |
not a machine in the ordinary use of this word, but is an instrument involving the principle of the lever, which is used to determine when the weights of two bodies are equal. It consists essentially of a hori- zontal beam, carrying at its ends, by means of knife edges, two " pans," arid sup- ported at its middle poin... |
e explained if he assumed that this force obeyed the foil. \v : Between two particles of matter whose masses are m, and m,and which I-IM-ICH — 9 I-"-' 130 MECHANICS are at a distance r apart, there is a force of attraction propor- tional to * 2. This can be expressed by writing /= Gr *2, where Gr is a constant of propo... |
, this acceleration is. So, since r and T are both known, it can be calculated. If this acceleration toward the earth is due to gravitation and if Newton's law is true, it can also be calculated in terms of the acceleration of a falling body at the surface of the earth, i.e. g. For, using again the general formula, in ... |
other portions of matter than the earth and the sun, of variations in their distances apart, of the departure of the earth from a spherical form, etc. ; but all these irregularities can be fully explained as consequences of this law of gravitation. I is the science of •• <;ra\ national Astronomy." 4. The "Cavendish ex... |
value is 5.5270 4 TrCrr on the C. G. S. system. As will be shown later, the value of the density of water at ordinary temperature does not differ far from 1 on this same system ; and so the density of the earth is about 5J times as great as that of water. The student should consult Mackenzie, The Laws of Gravi- tation... |
onism of a pendulum ; and he made use of this fact in cer- tain observations. He also, in 1641, described a plan of using a pendulum to regulate a clock, and had a drawing of his invention made. This fact was not generally known, how- ever; and in 1656 Huygens independently invented a pen- dulum clock, which came into ... |
accord with the principles enunciated on. and the\ have served for over two hundred years as the basis of all work in Mechanics. \e\\toii t hus int induced the ideas of ni;i^s,iiid of the proper measure of an\ force. I'.- fore NeWton'> ideas \\cl-e accepted, there \\as a dispute as to the value to be assigned "quantit... |
most useful book of reference for elementary students. CHAPTER IV PROPERTIES OF SIZE AND SHAPE OF MATTER Solids and Fluids ; Liquids and Gases. — The most obvious property of a material body is that it has a certain shape and size, both of which can be changed by suitable forces. As has been explained before, the name... |
made. This proves that the fluid layers on the inner surface of the tube stick to it, and so the fluid actually flows through a tube of the same material as itself. Consequently, in this flow the velocity is zero at the surface of the tube and increases toward the axis ; and so layers of the fluid flow over each other... |
the water in a very finely divided state. If colloids are mixed with not too much water, they form jellies OF membranes ; and crystalloids are able to diffuse through many of these with almost as much ease as through pure water. This process is called "osmosis," and one case of it will l)e discussed later. (This evide... |
is reached such that, if more is intro- duced, it does not dissolve, but remains as a solid pre- cipitate: the solution is said to be "saturated." If the temperature is lowered, salt will be precipitated if some solid salt is already present; otherwise, this does not in general take place. If the liquid thus contains ... |
a molecule strikes tin- surface with suffici cut velocity it may escape, and thus evapo- ration is explained. In a gas we assume that the forces between the molecules are so minute that the freedom of motion is practically perfect; they can move freely from any point to another in the space open to them; and we think ... |
i- cal value is defined as follows : let the internal force between two portions of the body whose area of contact is A have the value F, then the limiting value of the ratio — as A is made smaller and smaller is that of the stress at that point. (If the stress is uniform, it equals the force per unit area.) Owing to t... |
is, in accordance with Hooke's proportional to it. and therefore the acceleration is I Again, if I lookers law is true, the elastic force corresponding to any displacement must!»«• directly propt.rt ionul to it, as has just been said; HO, if/ is the value of tin nd x that of the displacement/^ or, where c is a factor.... |
.00021. 0.0000895. 0.001257. 0.001429 WATER AT DIFFERENT TEMPERATURES 0°C.. 1° 2° 3° 4° 5° 6° 7° 8° 9° 10° 11° 12.999878. 0.999933. 0.999972. 0.999993. 1.000000. 0.999992. 0.999969. 0.999933. 0.999882. 0.999819. 0.999739. 0.999650. 0.999544. 0.999430. 0 999297 0.999154 16° C... 0.999004 17°.... 0.998839 18°.... 0.99866... |
removed. It tin- load is increased still more, the elongation becomes greater; and at length a condition is reached sueh that. greater force is applied, the extension increases v< i \ rapidly and the wire becomes plastic, because the amount of the ex- tension now varies with the time the load acts. This point is calle... |
is — • This stress A i% acting across all the planes of the block that are parallel to the boards. The coefficient of elasticity for a change in shape is, then, the ratio <>f this ipiantity to the angle referred t<> j." 152 MECHANICS r 7i above. This coefficient is also called the "coefficient of rigidity"; and the pa... |
third the actual mass of the spring. CHAPTER VI FLUIDS General Properties. — Fluids have been defined as those bodies \vhieh yield to any force, however small, which acts in such a manner as to cause one layer to move over another; that is, they yield to shearing forces. There are two classes of fluids: liquids and ga... |
at the point considered, in the direc- tion of the force. If the pressure is uniform, it equals, then, the force per unit area. We thus speak of the pressure at the bottom of a tank of water, etc. Pressure at a Point. — At any point of a fluid at rest the pressure has the same value in all directions ; for, consider a... |
is given by the point F, and the work done by it equals the area of the rectangle BEFC'. It is at once evident that, if the changes in pres- sure and volume occur, not in a discontinuous manner as from D to 0 to O' to F, etc., but continuously, as represented by a smooth curve PQ, the work done during any change in vo... |
i.-es, such as gravit\ — this is, in fact, the only such force which we need, in general, consider. Illustration the former muse, t* sho\\ii by balloons, dams, and have.re : hut to have one where the prcs is due entireU to the containing walls, we must imagine a AMES'S 1'iiYBics — 11 162 MECHANICS fluid in its vessel c... |
volume is made very small; but if it is a liquid, the pressure may be made as great as desired without any marked decrease in volume. Thus, FLUIDS water or some other liquid as the fluid in a cylinder provided with two pistons, a small force acting on the smaller piston may produce a great force by means of the larger... |
weight is dhAg, because hA is the volume and dhA the mass. Therefore the excess of pressure due to the vertical height h is dgh. It follows that the pressure at all points in the same horizontal plane of a fluid is the same ; because, if it were different, there would be a flowing of the fluid from the point of high p... |
of the specific gravity of a solid body in terms of any liquid which does not dissolve •i ise affect it If the weight of the solid is measured when Tee, its value is mg or dvg, when d is its density and v ito volume, due allowance being made for the bu<> If it is weighed again, hanging imineraed in the liquid, the dif... |
any moderate dimensions. There are, however, marked differ- ences in the pressure of the surrounding atmosphere in which we live as one rises far above the earth's surface or goes up a mountain. This is owing to the large value of h in the above formula, which may in this manner be secured. Owing to the presence of th... |
pressure due to the containing walls equals the atmospheric pressure, and, as said above, this pressure is the same at all points in the liquid. Fluids in Motion If there is a difference in pressure between two points in.1 tlnid. tin i, will be mot: 11 high to low pressure unless re vents it. We shall consider several... |
rr«ruir in the air is greater. iff to this fact the ball is pushed sidewiae in the direct A to*. 170 MECHANICS Solid moving through a Fluid. — As a solid moves through the air, there are forces that oppose its motion ; and many experiments have been performed to determine the connec- tion between this force and the vel... |
is A, is (P-f dgH) A\ and the thrust on the side wall, if it is rectangular and vertical, is the average pressure multiplied by the area of the wall in contact with the liquid. If this area is A, the thrust is then (P + J dgH) A. Its point of application is found from the consideration that it is the resultant of a gr... |
heavier of the two liquids will occupy the bottom of tlio tube and rise to a certain height in one of the arms, while the lighter one will stand to a greater height I in the other. The pressure at the fl surface of contact between the two I liquids is the same as at a point in '«! — *-- the heavier liquid at the same ... |
at once calculated from the observed barometric height. In the formula, h is the height in centimetres. Sometimes, how- ever, the reading is made on a divided scale which is correct at 0° C. ; and in this case the readings must be corrected in order to give A. If the scale is made of such a material that each centimet... |
r is vertically through the centre of gravity of the di-jilaccd liquid: that of the latter, vertically through the <«ntre of gravity of the floating body. Therefore, when there is equilibrium, these two centres of gravity must lie in thcsamr vertical line; otherwise there would he a moment which would make tin- body t... |
d, that of the solution does not differ much from this ; and if the difference in level of the two free surfaces is h, the hydrostatic pressure dgh measures this tendency of the pure solvent to pass through the membrane into the solution, that is, it measures the effect the dissolved sub- stance has upon the solvent i... |
earth; and therefore, if the jet 182 MECHANICS were turned upward, it would rise to the height of the level of the liquid in the vessel, were it not for the opposing action of the air. (This formula was first deduced by Torricelli.) The pressure in the liquid at the opening is P + dgh, while that on the outside is P ;... |
< >\v the plate ; and, as it contracts, it rounds off the corners, thus leaving a free space which the force of gravity would cause the liquid to till were it not for the contracting force of the surface. There is equilib- rium, then, when these two forces balance each other. This phenomenon in the neighbor- Fio. 91. -... |
into soapy water and then removing it.) It will be found that a force must be exerted on the movable wire to keep the film from contracting. Calling the length of the movable wire Z, this force equals 2 Tl, because the film has two surfaces. If under the action of the force the wire is moved so as to make the film lar... |
l f.. i -mn la, no reference is made to the cross section of the tube except at the point where the top of the column «.f liquid comes ; so the tul>e elsewhere can have any size. The liquid will nut rise in the tuhe of it*, If unless the bore is 1 throughout and the inner wall is \vet witli the liquid. if the liquid is... |
and the air, T9 190 MECHANICS between the oil and the air, Tj between the oil and the water. The oil spreads because 7'3 is greater than the resultant of T2 and Tr This thin layer of oil will prevent the dissolving of the camphor, and its motions will cease. If a drop of alcohol is poured on a glass plate that is cove... |
AMES'S PHYSICS — 13 194 MECHANICS that there is no time for the temperature effect to become weakened by diffusion. The former is called an "isother- mal" change ; the latter, an "adiabatic" one. Boyle's Law and its Consequences Boyle's Law. — The first philosopher to study experimen- tally the exact properties of gas... |
The formula pv = constant is known as the "equation of condition " for an ideal gas at constant temperature, or as the equation of an "isothermal" for a gas ; and, as has been said, it is only approximately true for an actual gas. Other formulae have been proposed which apply more exactly to ordinary gases over wider ... |
is done by the in overcoming the external force. Similarly, if the movable portion of the wall is forced in. work is done on the gas; and it is evident that the linear velocity of a particle rehnundini: iiat instant is increased, and BO the kinetic energy of translation of the particles of the LTas is increased. K\ ; ... |
d, or the 200 MECHANICS mass in a unit volume, is 7HJV; hence the pressure may be written i This states that, if the mean kinetic energy of translation of the particles does not change, the pressure varies directly as the density. This is Boyle's law, assuming that the tem- perature of a gas corresponds to the mean ki... |
they can move about uninfluenced by other particles except when they come very close together, i.e. when they have what may be called an "encounter." In the interval of time between two encounters the particle is moving in a straight path with a constant speed ; the length of this path is called the "free path," and i... |
the order of 2 x 1019, i.e. twenty quintillions. Fourth State of Matter. — If a gas is inclosed in a glass bulb which can he gradually exhausted by means of an air pump, as will be explained later, the most evident change produced is the decrease in density and the consequent increase in length of the mean free path. ... |
high cylindrical till).' ) \\ hi< 1 ihe wlie- under great pi* -T is admitted through the Ml 206 MECHANICS turbine near its axis, flows out along the flanges, and escapes at the edges, so that the wheel is set in rotation by the pressure. In a similar manner steam can be used to drive a turbine, as is done in the so-ca... |
pressure throughout the whole tube, the outlet valve Q is pushed up and some water enters the air chamber ; then the valve drops as the pressure is thus relieved, and the operation is re- peated. As more and more water enters the air chamber, a time is reached when the level of the water covers the open end of the out... |
well into another at a greater height, or for forcing a liquid through a long pipe against friction. There are two types : the u lift pump " and the " force pump." The former consists of a cylinder in which fits an air-tight piston provided with a valve B opening upward, and whose lower end is closed by a valve A, als... |
the difference in pressure of the gas on the two sides of the \al\cs is nut snrtieient to move them. Such pumps as this are called "mechanical" ones. Other forms in general use are the Sprengel and the Geissler-Toepler. AMES'S PHYSICS — 14 210 MECHANICS b. Sprengel pump. — The action of this purnp consists in having d... |
cm. long and is connected at its lower end to a large vessel of mercury by means of a long rubber tube. The upper tube is bent over into a vertical direction downward, and dips into a basin of mercury, or forms a trap. Around the large bulb there is a branch tube connecting the upper and lower tubes just as they leave... |
A most interesting and useful text-book. RISTEEN. Molecules and the Molecular Theory of Matter. Boston. 1895. A popular, yet accurate, description of the kinetic theory of matter. HOLMAN. Matter, Energy, Force, and Work. New York. 1898. This is a philosophical discussion of the properties of matter. POYNTING AND THOMS... |
in the case of an elastic body by setting it in vibration, or by sending waves or pulses through it ; for under these conditions the kinetic and potential energies of the molecules are altered. Thus a bell if struck by a hammer vibrates, and as a result waves are produced in the surround- ing air, the particles of whi... |
properties with the exception of their mass and weight change. Tim-. M <»f iron is exposed to the Hun or put on a stove, its volume increases, its elasticity < -han^es, it feels hot 116 216 HEAT to our fingers. If a piece of ice is put in a basin on a stove, it changes its state, becoming a liquid ; this water gradual... |
process, work is done on or by whatever external force or pressure is acting on the body maintaining its volume, and, in general, by the force of gravity also. Thus, if a pillar supporting a build- ing expands, the building is raised and work is done ; the air presses against the sides of the pillar, and this force is... |
is called "heat energy," and the effects that bodies experience when they gain or lose this energy are called "heat effects." In ordi- nary language the word "heat" is often used in place of heat energy, and we speak of k% adding heat to a body/ OK withdrawing it, of a "source of heat." etc., where the mean- ing is ob... |
; or, in other words, the temperature or hotness of a gas is due to and is measured by the kine'tic energy of translation of its molecules. There are many reasons for believing that this is true also of solids and liquids ; and so, when the temperature of a body is raised, we believe that the kinetic energy of its mol... |
} and /., ; then some definite p of a definite. which can be ni.M>uied and \\hich changes with the •2'2-J. HEAT temperature, is selected ; its numerical value is determined in the two standard conditions and in the one to which a number is to be assigned — let these values be ar «2, and a ; finally, the number for the ... |
the standard tem- peratures must be noted, and the volume of different portions of the stem must be measured, in order to determine exactly the error of each division as marked by the maker. Moreover, a glass thermometer is subject to an error due to two facts : a glass bulb whose temperature is raised from one value ... |
are concerned with the quantity of energy that must be added to or withdrawn from a body in order to produce a given change ; and so a convenient unit must be chosen, and suitable methods of measurement must be devised. The scientific unit for the expression of amounts of all kinds of energy, including therefore heat ... |
187 x 107; that is, it is 4.187 joules. The great disadvantage in having as a "heat unit" one that depends upon a range of temperature (other than from 0° to 100° C.) lies in the difficulty of determining temperature accurately, and in the fact that so many arbitrary quantities and ideas enter into the definition of a ... |
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