Pendulum Tension

This experiment simulates a energy/forces problem common in many college-level text books.

Lab Summary

In this experiment, a mass on a pendulum is released from a height in such a manner that the pendulum's string is initially parallel to the floor. As the mass descends, the string strikes a rod. The objective is to find the minimum distance (d) (between the top of the pendulum and the pivot point) for which the string remains taut as the bob reaches its maximum height after the string strikes the rod.

Set Up & Procedures:

Measure and record the length (l) of the pendulum.
Measure and record the length (d).
Raise the bob so that the string is parallel to the floor and taut.
Release the bob.
Observe whether the bob remains taut when it reaches the maximum height after the string strikes the pivot point. If it does remain taut, move the pivot point upward several centimeters.
Repeat the previous steps (2-4) until the bob does not remain taut. Measure the distance, d, when the bob does not remain taut.

Questions:

Draw a force (free body) diagram of the mass when it reaches its maximum height after the string strikes the pivot point.
Derive an algebraic expression for the minimum distance, d, in terms of the length, l, for which the string remains taut.
Compare your theoretical value of the minimum distance, d, with the experimental value. Explain any differences.

Published: September 2007