Fric·tion n.
 1. The act of rubbing the surface of one body against that of another; attrition; in hygiene, the act of rubbing the body with the hand, with flannel, or with a brush etc., to excite the skin to healthy action.
 2. Mech. The resistance which a body meets with from the surface on which it moves. It may be resistance to sliding motion, or to rolling motion.
 3. A clashing between two persons or parties in opinions or work; a disagreement tending to prevent or retard progress.
 Angle of friction Mech., the angle which a plane onwhich a body is lying makes with a horizontal plane,when the hody is just ready to slide dewn the plane.
 Note: This angle varies for different bodies, and for planes of different materials.
 Anti-friction wheels Mach., wheels turning freely on small pivots, and sustaining, at the angle formed by their circumferences, the pivot or journal of a revolving shaft, to relieve it of friction; -- called also friction wheels.
 Friction balls, or Friction rollers, balls or rollers placed so as to receive the pressure or weight of bodies in motion, and relieve friction, as in the hub of a bicycle wheel.
 Friction brake Mach., a form of dynamometer for measuring the power a motor exerts. A clamp around the revolving shaft or fly wheel of the motor resists the motion by its friction, the work thus absorbed being ascertained by observing the force required to keep the clamp from revolving with the shaft; a Prony brake.
 Friction chocks, brakes attached to the common standing garrison carriages of guns, so as to raise the trucks or wheels off the platform when the gun begins to recoil, and prevent its running back. --Earrow.
 Friction clutch, Friction coupling, an engaging and disengaging gear for revolving shafts, pulleys, etc., acting by friction; esp.:  (a) A device in which a piece on one shaft or pulley is so forcibly pressed against a piece on another shaft that the two will revolve together; as, in the illustration, the cone a on one shaft, when thrust forcibly into the corresponding hollow cone b on the other shaft, compels the shafts to rotate together, by the hold the friction of the conical surfaces gives. (b) A toothed clutch, one member of which, instead of being made fast on its shaft, is held by friction and can turn, by slipping, under excessive strain or in starting.
 Friction drop hammer, one in which the hammer is raised for striking by the friction of revolving rollers which nip the hammer rod.
 Friction gear. See Frictional gearing, under Frictional.
 Friction machine, an electrical machine, generating electricity by friction.
 Friction meter, an instrument for measuring friction, as in testing lubricants.
 Friction powder, Friction composition, a composition of chlorate of potassium, antimony, sulphide, etc, which readily ignites by friction.
 Friction primer, Friction tube, a tube used for firing cannon by means of the friction of a roughened wire in the friction powder or composition with which the tube is filled.
 Friction wheel Mach., one of the wheels in frictional gearing. See under Frictional.

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 Horse pow·er
 1. The power which a horse exerts.
 2. Mach. A unit of power, used in stating the power required to drive machinery, and in estimating the capabilities of animals or steam engines and other prime movers for doing work. It is the power required for the performance of work at the rate of 33,000 English units of work per minute; hence, it is the power that must be exerted in lifting 33,000 pounds at the rate of one foot per minute, or 550 pounds at the rate of one foot per second, or 55 pounds at the rate of ten feet per second, etc.
 Note: ☞ The power of a draught horse, of average strength, working eight hours per day, is about four fifths of a standard horse power.
 Brake horse power, the net effective power of a prime mover, as a steam engine, water wheel, etc., in horse powers, as shown by a friction brake. See Friction brake, under Friction.
 Indicated horse power, the power exerted in the cylinder of an engine, stated in horse powers, estimated from the diameter and speed of the piston, and the mean effective pressure upon it as shown by an indicator. See Indicator.
 Nominal horse power Steam Engine, a term still sometimes used in England to express certain proportions of cylinder, but having no value as a standard of measurement.
 3. A machine worked by a horse, for driving other machinery; a horse motor.

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