1. (75%) Practice rotational motion problems by completing
WeBWorK set # 7.
2. (25%) In the software download area of the Physics 121
website, located at
http://teacher.pas.rochester.edu/phy121/Software/SoftwareIndex.htm,
you will find a movie that shows a single puck spiraling
inward on a horizontal air table. The inward spiral is caused by a falling
mass that is attached to the spiraling air puck by means of a string
that passes through a small hole at the center of the air table. Use
video analysis to determine if angular momentum is conserved.
Use the following steps in this analysis:
a. Download
the movie clip from the Physics 121 website.
b. Start LoggerPro.
c. From the
“Insert” menu, select “Movie” to open the movie
you want to analyze.
d. At the bottom
right-hand side of the video window you see a button with red dots
with allows you to “Enable/Disable Video Analysis”. Enable
video analysis a set of tools will appear on the right-hand side of
the video window.
e. Select the
ruler button to set the scale. Use the rulers on the left-hand side
of the video to calibrate your screen. After selecting the ruler button
you move your mouse to one end of the “ruler” in the video,
click-and-hold your mouse button, move your mouse to the other end of
the “ruler,” and release the mouse button. A window
will emerge, asking you for the length the
“green line” you just drew on the screen.
f. Using
the “Set Origin” button (the third button from the top
on the right-hand side of the movie window) to define the center of
the table as the origin of the coordinate system.
g. Use the
“Add Point button” (the second button from the top on the
right-hand side of the movie window) to define the center of the puck
in each frame, using your mouse. Each time you select a position
in a frame, the video will advance to the next frame.
h. After completing
your data entry you will see that the x and y positions
and velocities for all frames in the data table. These data can
be exported by selecting “Export as …. Text” from
the file menu. The file created can be opened with Excel and you
can use Excel to determine the angular momentum of the puck as function
of time.
Do you expect angular momentum to be conserved? If
yes, why? If not, why not?
Use the measured velocities and positions
to determine the angular momentum of the puck with respect to center
of the table and plot the angular momentum as function of time. Is
angular momentum conserved?
The solution to this problem (the graph and
your conclusions) needs to be dropped off in the Physics 121 homework
locker in B&L, across from B&L 106. Please make sure your
work is clearly labeled with your name.
Last updated on
Thursday, March 27, 2008 9:02
