Physics Java Labs

Before you start your lab report, it might be useful to look at a sample report.

Lab: Pendulum

  • Purpose of experiment:
    A pendulum is the classical example for an oscillator. Its length determines the period of oscillation - at least in the approximation of small amplitudes. This experiment has two purposes:
    1. To measure the period of oscillation as accurately as possible.
    2. To see if the period of a real pendulum depends on the amplitude of the oscillation.
  • Instructions for performing the experiment:
    1. Run the java applet by clicking this button:

      (It will open in a separate window).
      Please note: Each time you reload the applet, it will use a pendulum of different length. So please make sure that you conduct all of your measurements without closing this window.
    2. Grab the (red) bob of the pendulum with the mouse and move it to the desired starting angle. (While you drag the pendulum, the angle will be indicated in blue.) For now, please select a small angle. As soon as you let go of the pendulum, the computer-controlled stopwatch will start running.
    3. You can stop the stopwatch by pressing the "s" key on your keyboard. You can also take "lap-times" by pressing the keys "1", "2", or "3" on your keyboard.
    4. In the first series of measurements, please count 10 full oscillations of the pendulum and measure the time. Repeat this process 5 times, each time starting from exactly the same angle, and write down the measured times. In general you should expect some small differences between your individual measurements, because of your reaction time in pressing the keys on the keyboard.
    5. From your measurement you can now state a value of the period, T, and its uncertainty. Since you know the relation between T and the length of the pendulum, L, you can also give a value for L.
    6. Now that we have T in the approximation of small amplitudes, let us repeat the same experiment for larger amplitudes. For this part of the experiment, you should measure T for at least 6 different initital angles between 0 and 90 degrees by using the technique outlined above.
    7. Produce a plot of the period as a function of initial angle.
    8. Finally, write the report with your favorite word processor or text editor and email it (as email attachment) back to the instructor.
      Remark: You may want to know why we need to repeat measuring 10 oscillations for 5 times instead of measuring 50 oscillations all at once. The answer is that this pendulum, like all real pendula, has damping. And so the amplitude slowly decreases over time. While the effect of this is somewhat acceptable during 10 oscillations, it is not during 50.
  • Help:
    If you are not sure how to extract the mean value and error estimate from your measurements, you may want to consult your manual on error estimates.

© W. Bauer, 1999