Studio Physics I
Introduction to Circular Motion
In order to receive credit for a written answer, it must be expressed as a complete sentence.
For this activity you will need a movie called “FerrisWheel”. You can get it off of the
CD (go to VideoPoint folder, then Movies, then look for it in the list). You can also
transfer it from the course webpage (Go to “class activities”, scroll down to the bottom of
the page, RIGHT CLICK on the movie, choose “save link as” and watch were the file get
saved to. Once you have the movie file, open the Videopoint software, chose open movie
and open FerrisWheel.
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#2
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#6
1. The first thing that must be done is to calibrate our measurement tool. The diameter
of the Ferris wheel (shown on the first frame) can be used as the known length. It is
16.9 meters. Click on the ruler icon (#2 in the picture shown above) and follow the
instructions that appear on the computer screen. You will need to change the “known
length” field to match the diameter of the wheel. Do not change “scale origin” or
“scale type”.
2. 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.
3. Center the cursor over a point on the wheel that you think you can keep track of. We
suggest that you choose a point in the lower left-hand portion of the picture. This is
because these points remain easy to see for many frames of the movie. They will not
be obstructed by anything as the frames advance. Click on the point on the wheel that
you have chosen. The movie will advance to the next frame and a small O should
appear at the location you clicked on. The spot on the wheel that you chose should
have rotated through some angle. Click on the spot in its new location. Collect about
20 data points.
Copyright@1999, 2000 Cummings
4. Based on the trail of circles left on the movie image, does the Ferris Wheel appear to
be rotating with a relatively constant speed? Explain your reasoning.
5. Plot the x-position as a function of time and sketch the graph on your paper. Plot the
y-position as a function of time and sketch the graph on your paper.
6. Plot the velocity in the x-direction. When you do this, there will also be a column
added to the data table (#6 in the picture on the first page) that shows the values of the
velocity at the different moments in time. (You may have to scroll over to see it).
Plot the velocity in the y-direction. Is the velocity in the x-direction relatively
constant? Is the velocity in the y direction relatively constant? Write down the range
of values that you find for each. Remember, answer in a complete sentence.
7. In addition to the x and y components of velocity that we looked at above, let’s
consider the total velocity of the wheel. In general, how does one get the total
velocity from Vx and Vy (the components)? Calculate the total velocity from the x
and y components in your data table for the first two times listed in the table. Show
all your work on your activity write-up
8. Plot the magnitude of the total velocity of the ferris wheel. This is done in the same
way as you have made other plots, except you must chose MAGNITUDE (not x or y)
from the pulldown menu where you would usually chose x or y. Then chose
“velocity” and click ok. Do the first couple of data points agree with what you
calculated above? (They should) Is the magnitude of the total velocity (speed)
relatively constant? Based on the graph, what is the approximate value of the
magnitude of average total velocity? What is the largest difference between the
average and one of the total velocities in the data table? What is this difference as a
percentage of the average? (This percent difference is a crude indication of the
uncertainty in your measurement.)
9. What is the magnitude and direction of the centripetal acceleration of a passenger on
this Ferris Wheel at the highest point? What is the magnitude and direction of the
centripetal acceleration of a passenger on this Ferris Wheel at the lowest point?
10. What forces act on a person at rest at the top of the Ferris wheel? What forces act on
a person at rest at the bottom of the Ferris Wheel? What are the directions of these
forces? Draw a free-body diagram for the passenger at the highest point. Draw a freebody diagram for the passenger at the lowest point.
11. Do any of the forces that you discussed above disappear if the person begins to move
in circle? Do any new forces appear?
12. What is the period for the revolution of the Ferris Wheel? Show all your work in this
calculation.
Copyright@1999, 2000 Cummings