Introduction: Atwood's machine consists of two masses M and m, connected by a string passing over a pulley (Atwood's, 2005). The pulley is assumed to be frictionless. Atwood's machine was used to determine the acceleration of gravity.
2 heavy washers with closely matched masses
Procedure: The pulley was hung from a doorway and the wire weight hangers hung from it. Two large washers were placed on each hanger. A small washer was added to one side. This heavy mass was held at a measured distance above the floor and let go. A stopwatch was used to determine the time elapsed until it stopped. This step was repeated 5 times. Another small mass was added and the measurements repeated until five sets of data were obtained. The results were recorded in a table. The five values for average acceleration were plotted as a function of the quantity (m1-m2)/(m1+m2) and a line of best fit was drawn through the points. The slope of the line was determined and the value for g calculated.
The points fell in a reasonably straight line. The main deviations were with the lower values of (m1-m2/m1+m2). The value obtained for g was very close to the accepted value of 9.8m/s2. The main sources of error could be friction in the system, and measurement of the drop because it was very fast. An automatic timing device would make this measurement more accurate.