Force is that which tends to alter a body’s natural state of rest or of uniform motion in a straight line.

Force is measured by the acceleration which it imparts to mass—­i. e., mass x acceleration.

The unit of force, or dyne, is that force which, acting for one second on a mass of one gramme, gives to it a velocity of one centimetre per second.  The force with which the earth attracts any mass is usually called the “weight” of that mass, and its value obviously differs at different points of the earth’s surface The force with which a body gravitates—­i e, its weight (in dynes), is found by multiplying its mass (in grammes) by the value of g at the particular place where the force is exerted.

Work is the product of a force and a distance through which it acts.  The unit of work is the work done in overcoming unit force through unit distance—­i e, in pushing a body through a distance of one centimetre against a forch of one dyne.  It is called the Erg.  Since the “weight” of one gramme is 1 X 981 or 981 dynes, the work of raising one gramme through the height of one centimetre against the force of gravity is 981 ergs or g ergs.  One kilogramme-metre = 100,000 (g) ergs = 9 8 1 X 10^7 ergs.  One foot-pound = 13,825 (g) ergs, = 1 356 X 10^7 ergs.

Energy is that property which, possessed by a body, gives it the capability of doing work.  Kinetic energy is the work a body can do in virtue of its motion.  Potential energy is the work a body can do in virtue of its position.  The unit of energy is the Erg.

Power or Activity is the rate of work; the practical unit is called the Watt—­10^7 ergs per second.

A Horse-power = 33,000 ft—­Ibs per minute = 550 ft—­Ibs per second, but as seen above under Work, 1 ft—­Ib = 1 356 X 10^7 ergs, and under Power, 1 Watt = 10^7 ergs per sec a Horsepower = 550 X 1 356 X 10^7 ergs = 746 Watts; or, =EC/746=C^2R/746=E^2/(746 R) =HP where E = volts, C = amperes, and R = ohms.

The French “force de cheval” = 75 kilogramme metres per sec = 736 Watts = 542 48 ft—­lbs. per sec. = .9863 H.P.; or one H.P. = 1.01385 “force de cheval.”

Derived electrical units.—­There are two systems of electrical units derived from the fundamental “C.G.S.” units, one set being based upon the force exerted between two quantities of electricity, and the other upon the force exerted between two magnetic poles.  The former set are termed electro-static units, the latter electro-magnetic units.

III.  ELECTROSTATIC UNITS.—­

Unit quantity of electricity is that which repels an equal and similar quantity at unit distance with unit force in air.

Unit current is that which conveys unit quantity of electricity along a conductor in a second.

Unit electromotive force, or unit difference of potential exists between two points when the unit quantity of electricity in passing from one to the other will do the unit amount of work.