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Learning Introductory Physics with Activities

Paul J. Emigh, Rebecka Tumblin, Kathryn Hadley, Danielle Skinner

Section 5.23 Application: Precession

Exercises Review Activity

Suppose you have an object moving in a straight line to the right with velocity \(\vec{v}\text{.}\)

1.

Indicate the direction of the acceleration of the object in each of the following situations. In particular, how is the direction of the acceleration related to the direction of the velocity? Explain your reasoning.
  • the object speeds up
  • the object slows down
  • the object moves in a circle

2.

For each situation above, indicate the direction of the net force on the object. Explain your reasoning.

Exercises Changing the Direction of the Angular Velocity

As introduced in the video above, suppose you have an object rotating clockwise with angular velocity \(\vec{\omega}\text{.}\)

1.

For an object rotating clockwise (from your perspective), what is the direction of the angular velocity vector?
Answer.
Into the screen (away from you).

2.

Indicate the direction of the angular acceleration of the object in each of the following situations. In particular, how is the direction of the angular acceleration related to the direction of the angular velocity? Explain your reasoning.
  • the object speeds up
  • the object slows down
  • the angular velocity changes so that it traces out a circle—what do you think this motion looks like?

3.

For each situation above, indicate the direction of the net torque on the object. Explain your reasoning.
Precession refers to a type of motion in which a torque on a rotating object causes the direction of the axis of rotation to change, rather than causing the object’s rotation to speed up or slow down.
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