SM024     Atwood’s machine      circa 1960     Mechanics

  Galileo, in the early seventeenth century verified the laws of falling bodies by using inclined planes.   The object is to reduce the velocity so as to observe the motion better.   Also air resistance will have less influence on the motion.

  A convenient instrument to measure this motion was invented by Atwood at the end of the nineteenth century.   There is a flywheel over which hang two equal masses.   One of the masses is increased by a small amount and will fall over a vertical scale on the instrument.   The beginning and end of the fall are defined by a release mechanism and a stop respectively.   The motion can be studied by means of a trace drawn by an inked brush that oscillates at an accurately calibrated rate leaving a mark on a strip of paper connecting the two weights and passing over the flywheel.

  In an experiment using the apparatus an overweight is placed and the motion accurately timed for one, two and three seconds.   The mass will accelerate, transferring momentum to the flywheel.   The laws of motion can be verified by examining the distance/time curve derived from the trace.