Question

How would you construct a pendulum clock that is reliable under a variety of temperatures?

Answer 1

Procedure

1.      Hang all three pendulums and the protractor from the plate in the ceiling using the pendulum clamp and the heavy duty loop. (note: this procedure is quite specific to Davis High) Adjust all three pendulums to have exactly the same length from pivot point to center of mass of the bob.

2.      Attach the laser to the tripod and position the laser so the beam shines horizontally on the pendulum bobs at their centers of mass perpendicular to the pendulums’ plane of motion. Attach the light sensor to the ring stand gently, using the test tube clamp. Orient the light sensor horizontally, and position the sensor opposite the laser so that the laser shines into the sensor. Spread the laser and the light sensor far enough apart to give the pendulums plenty of room to swing.

3.   Connect the light sensor to the channel 1 input on the CBL 2 or the LabPro. Use the black link cable to connect the interface to the TI Graphing Calculator. Firmly press in the cable ends.

4.   Turn on the calculator and start the DATAMATE program. It should show the light sensor in channel 1.

5.   Set up the calculator for time graph.

a.    Set the timing interval to 0.1 seconds.

b.    Set the number of intervals to 100.

c.    Zero the light sensor at ambient light levels.

a.    Return to main Datamate screen.

6.   Check the reading on the calculator screen; you should see --0--. Turn on the laser. Temporarily hold the bobs out of the path of the light beam. You should now see a nonzero reading, which indicates that the laser is hitting the sensor. Allow one of the pendulums to swing back and forth interrupting the beam. Check the reading and make sure it is alternating between the zero and nonzero readings.

7.   Now you can perform a trial measurement of the period of your pendulum. Hold the mass from about 10º from vertical and release. As the pendulum swings back and forth it will block the laser beam twice during each period. Verify that a proper graph is being generated.

8.         The graph should go from high to low every time the light beam is blocked. The period of the pendulum should be the distance along the time axis from the beginning of one low area to the beginning of the second low area following it.

9.   Measure the width of a low area each time you make a new data run and record it alongside the data table.