Note:  Do not rely on this information. It is very old.

Atwoods Machine

Atwood's Machine, an instrument for investigating the laws of uniformly accelerated motion. It consists of two unequal masses P and Q, connected by a fine silk thread passing over a pulley. That the friction at the pulley may be negligible, the axle does not rotate on pivots, but just rests on the circumferences of four other pulleys, two each side, as shown in the figure. The difference in the weights of p and Q produces downward motion of the heavier mass, say P, and upward motion of Q. Either mass may be varied while in motion, and the time taken to traverse any length may be recorded by an electric chronograph, water-clock, or other such time measurer. The space traversed is determined by a vertical scale fixed to the instrument. The observations thus taken enable us to determine the laws of such motion, and, indirectly, to determine G, the acceleration clue to gravity (q.v.).