
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:
 To measure the period of oscillation as accurately
as possible.
 To see if the period of a real pendulum depends on
the amplitude of the oscillation.
 Instructions for performing
the experiment:
 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.
 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 computercontrolled
stopwatch will start running.
 You can stop the stopwatch by pressing the
"s" key on your keyboard. You can also
take "laptimes" by pressing the keys
"1", "2", or
"3" on your keyboard.
 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.
 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.
 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.
 Produce a plot of the period as a function of
initial angle.
 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.
