If a body whose mass is m grammes be moving with a velocity of v centimetres per second relative to the earth, the available kinetic energy possessed by the system is Zmv 2 ergs if m be small relative to the earth.
The dynamical equivalent of the calorie is 4.18 X Io 7 ergs or C.G.S.
The closed figure a c d e a is variously called a hysteresis curve or diagram or loop. The area f HdB enclosed by it represents the work done in carrying a cubic centimetre of the iron through the corresponding magnetic cycle; expressed in ergs this work is I HdB.
When the magnetizing current is twice reversed, so as to complete a cycle, the sum of the two deflections, multiplied by a factor depending upon the sectional area of the specimen and upon the constants of the apparatus, gives the hysteresis for a complete cycle in ergs per cubic centimetre.
Denoting by W the work in ergs done upon a cubic centimetre of the metal (=_fHdB or f HdI), he finds W =nips approximately, where n 47r is a number, called the hysteretic constant, depending upon the metal, and B is the maximum induction.
Working with two different specimens, he found that the hysteresis loss in ergs per cubic centimetre (W) was fairly represented by o 00125B 1 6 and o o0101B 1 ' 6 respectively, the maximum induction ranging from about 300 to 3000.
Parshall quotes tests of six samples of iron, described as of good quality, which showed an average hysteresis loss of 3070 ergs per c.cm.
In many experiments, however, different inductions and frequencies are employed, and the hysteresis-loss is often expressed as ergs per cubic centimetre per cycle and sometimes as horse-power per ton.
Taking the density of iron to be 7.7, the factor for reducing the loss in ergs per c.cm.
After one of the rings had been annealed at 840°, its maximum permeability at ordinary temperatures was 4000 for H =1.84; when it had been subsequently annealed at 1150°, the maximum permeability rose to 4680 for H =1.48, while the hysteresis loss for 2 B = t 4000 was under 500 ergs per c.cm.
Hysteresis Loss in Ergs per c.cm.
8 The hysteresis of the soft annealed iron turned out to be sensibly the same for equal values of the induction at - 186° as at 15°, the loss in ergs per c. cm.
In one case the hysteresis loss per cubic centimetre per cycle was 16,100 ergs for B =1 5,900, and only 1200 ergs for B = 20,200, the highest induction obtained in the experiment; possibly it would have vanished before B had reached 21,000.2 These experiments prove that actual friction must be almost entirely absent, and, as Baily remarks, the agreement of the results with the previously suggested deduction affords a strong verification of Ewing's form of the molecular theory.
Having a charge Q repels a unit charge placed at a distance x from its centre with a force Q/x 2 dynes, and therefore the work W in ergs expended in bringing the unit up to that point from an infinite distance is given by the integral W = Q x 2 dx = Hence the potential at the surface of the sphere, and therefore the potential of the sphere, is Q/R, where R is the radius of the sphere in centimetres.
1 ergs / second.
According to modern measurements the solar radiation imparts almost 3 grammecalories of energy per minute per square centimetre at the distance of the earth, which is about Iï¿½3 X io s ergs per sec. per cm.
Just outside the earth's atmosphere is therefore about 4XIo 5 ergs; applying the law of inverse squares the value near the sun's surface would be Iï¿½8 ergs.
Let E be the effective elasticity of the aether; then E = pc t, where p is its density, and c the velocity of light which is 3 X 10 10 cm./sec. If = A cos" (t - x/c) is the linear vibration, the stress is E dE/dx; and the total energy, which is twice the kinetic energy Zp(d/dt) 2 dx, is 2pn2A2 per cm., which is thus equal to 1.8 ergs as above.
System of expression in ergs per gramme-degree-centigrade, or " calorie," is the most appropriate, as being independent of the value of gravity.
A more convenient unit of work or energy, in practice, on account of the smallness of the erg, is the joule, which is equal to 10.7 ergs, or one watt-second of electrical energy.