Studio Physics I
Introduction to two-dimensional Motion
In order to receive credit for a written answer, it must be expressed as a complete sentence.
1. Open the Videopoint software. Close the introduction box. Chose open movie. Go
to your program folder, then the VideoPoint folder, then the Projectile folder and open
the movie called PASCO106. After loading, your computer screen should look like
the image below.
#4
#
2
#5
#3
#6
2. Click “OK” to track one object. Next, we must calibrate our measurement tool. For
this software, that means telling the computer what distance on the computer screen
corresponds to a known distance that is shown in the movie. For example, you can
use either of the two meter-sticks. To calibrate the software, click on the ruler icon
(#2 in the picture shown above) and follow the instructions that appear on the
computer screen. (The object of “known length” in this case is a meter stick, so you
need to click on the two ends of one of the meter sticks). Do not change “scale
origin” or “scale type”.
3. Click on the icon #3 shown in the figure above. This will instruct the software to
leave a trail of markers at every location that you point the cursor to and click.
4. Center the cursor over the small white ball shown in the figure and click. The movie
will advance to the next frame and a small o should appear at the location of the
cursor at the time you clicked the mouse. Take the time to center over the ball VERY
carefully. It is easier to take good data the first time than to have to re-measure later.
Copyright@1999 Cummings
Collect seven data points by leaving seven points on the screen. Note: When the
cursor is in the movie window, it should look like the top icon (#4 in the figure
above). If the cursor does not look like this when you have it centered on the ball,
click on the top icon (#4) and the problem should be corrected.
5. In terms of x, y and t, what is the trail of circles a graph of? (That is, is it a graph of x
vs. t, y vs. t, y vs. x or what?)
6. Use the software to plot x vs. t This is done by clicking on icon # 5 (shown in the
picture above). Make a sketch of the graph on your activity sheet. Is the velocity in
the x-direction (Vx) constant or changing? How do you know from the graph? What
is ax?
7. Use the software to plot y vs t
Make a sketch of the graph on your activity sheet.
Is Vy constant or changing? How do you know? What is ay?
8. Consider an object that is shot through the air, like the ball in this video clip. How
does the acceleration due to gravity change for the object as it rises, reaches its
highest point and then starts to come back down? Use the software to plot ay versus t
and sketch that graph on your paper. Does your graph support your answers to this
question and the question above?
9. As time goes on, how does the ay affect the velocity in the x-direction?
10. According to your data, what is the value of xo for the motion of this ball?
11. Use the software to plot the velocity of the ball in the x direction. What is vo,x?
12. Rewrite xf = xo + vo,xt + ½ axt2 , replacing variables with the values that you
determined above.
13. What is yo, what is vo,y what is ay? (Make any plots you desire in order to determine
these values)
14. Rewrite yf = yo + vo,yt + 1/2ayt2, replacing variables with the values that you
determined above.
15. Calculate the values of x and y that you would expect to measure 0.30 sec after ball
leaves its initial location. Show all your work. What do you need to know about the
motion in the y direction in order to determine the x position of the ball at t=0.30
seconds?
16. Return to the movie in VideoPoint and take the last few data points in the clip. What
values of x and y do you measure at 0.30 sec? If your measured values and the values
that you calculated in the step above are within 10%, you are done.
Copyright@1999 Cummings