AP Conservation of Angular Momentum

AP Conservation of Angular Momentum

Rotational Inertia

• More mass = more rotational inertia

• The farther the mass is from the point of rotation = more rotational inertia

Rotational Inertia

•  $I\ =\ \Sigma mr^2$  is the general equation for rotational inertia.

• You will not have to solve for I on the AP Physics 1 Exam, it will always be given to you.

Conservation of Angular Momentum

• In the absence of a net external torque (the system is isolated) the net angular momentum of a system is conserved.

• Moment of Inertia and Angular Velocity change inversely as mass distribution changes.

Angular Momentum Formula

• L is the Angular Momentum

• I is the Moment of Inertia

• ω is the Angular Velocity

Notice changes in angular velocity and rotational inertia.

Multiple Choice

According to the Law of Conservation of Angular Momentum, if I (momentum of inertia) increases, what will happen to ω?

• Decrease

• Stay the same

• Increase

Multiple Choice

In order to do a lot of flips an Olympic diver would want:

• A high rotational inertia
• A low rotational inertia
• A low linear acceleration
• A low angular velocity

Multiple Choice

Which has greater angular speed, a horse near the outside rail of a merry-go-round or a horse near the inside rail?

• The inside horse
• The outside horse
• Neither - they both have the same angular speed

Multiple Choice

Two children, Ahmed and Saleh, ride on a merry-go-round. Ahmed is at a greater distance from the axis of rotation than Saleh. Which of the following are true statements? 

• Saleh and Ahmed have the same tangential speed.
• Ahmed has a greater tangential speed than Saleh.
• Saleh has a greater angular speed than Ahmed.
• Saleh has a smaller angular speed than Ahmed.

Multiple Choice

A person sits on a freely spinning lab stool that has no friction in its axle. When this person extends her arms,

• her moment of inertia increases and her angular speed decreases.
• her moment of inertia decreases and her angular speed increases.
• her moment of inertia increases and her angular speed increases.
• her moment of inertia increases and her angular speed remains the same.

Multiple Choice

Stars originate as large bodies of slowly rotating gas. Because of gravity, these clumps of gas slowly decrease in size. What happens to the angular speed of the star as it shrinks?

• It rotates faster.

• It rotates slower.

• It starts to accelerate in the forward direction.

• The rotation rate stays the same.