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Sound and Music: Friction

Pumps are machines which demonstrate the pressure of the atmosphere by raising water into a vacuum. The hydraulic ram raises water through a valve by the lateral action of a current within a pipe. It rises in an air vessel, and the re-action of the air forces the water up a tube placed in the water. Friction is the parting with motion or force to surface in contact with the mover; and resistance is the parting with motions to the atoms of any medium through which a body in motion is passing. Friction varies with the nature of the surface rubbed, and with the weight or downward force of the mover. It is the friction of twisted fibres that gives strength to all fibrous substances. Friction checks all great natural motions by carrying off their excess.

Balls ascend when directed horizontally because their velocity is greater than the earth's rotation, and for the instant they lose the force of gravity or weight. A man or horse will perform his labor with the greatest advantage when the resistance is four-ninths of his natural strength, and when his velocity is equal to onethird of his greatest velocity when not impeded. The force of a man at rest is about 70 lbs., and his velocity, 6 ft. When not impeded therefore his force is exerted to the best advantage by a resistance equal to 31 lbs., and a velocity of 2 ft. per second. A horse's greatest pull is 420 lbs., equal to 20 cubic ft. of steam per minute; and his rate, 10 ft. a second; therefore a horse's labor is best performed at 187 lbs., and 3 ft. 4 in. per second.

A man unloaded can walk 3½ miles per hour for 10 hours without prejudice; that is 308 ft. per minute, or 5 ft. per second.