You can also click on the picture to download it in .gif format.
Further information on the Theory, Apparatus, and Procedure is available. Equipment is stored in Rockerfeller Room 302 and 302B.
In theory, all strings in a frictionless pulley system possess the same tension. Hence, the number of supporting strings of an object multiplied by this tension is equal to the total supporting force on the object. To move the object a distance x, each supporting string must be lengthened or shortened by this distance. Thus, x amount of string multiplied by the number of strings whose length must change must be pulled through the system to raise or lower an object. The total force applied is equal to the tension of the string, conserving energy.
Similar principles apply for a lever, with any force multiplied by its distance from the fulcrum on one side being equivalent to the force on the other side multiplied by its distance from the fulcrum if the angular acceleration of the system is constant. By drawing similar triangles it can be shown that the distance travelled by a part of the lever multiplied by the force applied to it on one side is equal to the distance travelled by a part of the lever on the other side of the fulcrum multiplied by the force applied to it.
The equipment needed for this demo is:
As the name simple machines implies, the setup is not complicated. To actually measure forces, spring force gauges can be attached to the ends of levers and to the pulley strings. Forces can be created by attaching masses to the ends of the levers and strings. It is possible, however, to make a slightly more involved calculation by bootstrapping two of the machines. One example would be to attach the end of a lever to a pulley string, with an extra pulley in the system. Then a weight on the other end of the lever could balance another weight attached to the pulley.
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