Reading Quiz 18 Key

Due 3:30 pm, Thursday, October 29th

Physics 105, Fall Term, 2009


Reading: Chapter 8.7

Did you complete the reading assignment?

Yes
No

KEY CONCEPTS:

1) Angular momentum is the rotational version of momentum.

2) Angular momentum is conserved.

Angular momentum is the momentum of an object as it applies to circular motion. Some people like to think of it as the quantity of circular motion because it involves not only the motion of the object but also its inertia. Like everything else we have studied in rotational motion, it is basically the same concept as its linear counterpart with equations altered to apply it to circular motion.

Which of the following equations is not a correct mathematical description of angular momentum?

L = Iω
L = pr sin θ
L = τt
L = mv2t
They are all correct

Exercise 1

Go to: http://phet.colorado.edu/sims/rotation/torque_en.jnlp again. This time, click the 'Angular Momentum' tab at the top of the applet. Leave the ladybug in place for the entire use of this applet, otherwise you may get confused. The controls for the applet are basically the same as the controls for the 'Moment of Inertia' tab from last reading quiz, but this one has a place where you can enter in the angular velocity of the rotating platform which makes it much nicer to use.

Play with the controls by changing the outer radius, inner radius, and mass of the platform using the scrollbars and changing the angular velocity by typing it into the box. Pay attention to the three graphs as you do this.

As the angular velocity increases, what happens to the angular momentum?

Angular momentum increases
Angular momentum decreases
Angular momentum stays the same

As the moment of inertia increases, what happens to the angular momentum?

Angular momentum increases
Angular momentum decreases
Angular momentum stays the same

Now apply a very small force for a short time to the platform by clicking the platform and dragging the mouse a small ways and letting go. Watch the angular momentum graph. Does it change after letting go of the force? Why or why not?

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Was there anything that you didn't understand in the reading assignment?  What was confusing to you?


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