Physics Java Labs
Before you start your lab report, it might be useful to
look at a sample
Determination of g
- Purpose of
Recording the trajectory of free-falling objects enables
us to extract their equations of motion and, in
particular, determine experimentally the value of the
gravitational acceleration, g, near the surface of
It is claimed that Isaac Newton was sitting under an
apple tree and was hit on the head by a falling apple,
which triggered the insight needed to come up with
Newton's universal law of gravitation. So we also drop an
apple for this experiment. But just for fun we used an
Apple computer. It makes a better smack when it hits the
- Video clip of
Larger size, (1.2 MB, with
sound) or smaller size (0.4
MB, no sound) versions are available.
- Instructions for performing
- Run the java applet by clicking this
button:(It will open in a separate window).
- Digitize the motion of the falling object by
clicking on it. After each click, the mouse position
is recorded and the movie is advanced one frame. You
should always try to click on the same point of the
computer while it falls. If you make a mistake, click
on the "Undo Pt." button
in the applet, and the last point will be erased.
Note: If you are using a
phone line to perform this experiment, then please
keep in mind that it can take a couple of seconds
between two successive frames of the video you are
digitizing. Please do not get impatient. You can see
when the next frame is ready for you from observing
the text area: as soon as the result of your previous
click is displayed, the next video frame is ready for
- You can display the points that you have already
digitized before by clicking on the "Plot y(x)"
button. It will turn red and show the points overlaid
on the video. Clicking the same button again will turn
this feature off.
- You can also plot the trajectory as a function of
time directly within the applet by clicking on the
"Plot y(t)" button. Clicking on the "Digitize" button
will bring you back to the data input mode.
- The numerical data you have collected are
displayed in the text area on the right side of the
applet. After you are done digitizing all frames,
please copy your data into your clipboard and export
them into your favorite spreadsheet or graphing
program. There, you can fit a parabola
y(t) = a + b·t +
to your data. The coefficient c will be
g/2, where g is the gravitational
acceleration near the surface of the Earth.
- Now produce a plot with your graphing program or
by screen-capture of the applet.
- Finally, write the report with your favorite word
processor or text editor and email it (as email
attachment) back to the instructor.