Conservation of Angular Momentum Lab
Introduction:
Just as we think of objects here on earth (cars, baseballs, runners) traveling with a linear
velocity, it is more convenient to describe the motion of rotating objects by their angular
velocity. Earth is a rotating planet, and therefore we describe its motion using angular
velocity.
Consider a bicycle wheel, with at marker attached to the rim, rotating about its axle:
If the marker rotates through angle α in time t, then the angular speed is ω = α/t. The
angular velocity ω has magnitude given by the top equation and orientation along the axis
of rotation (for the wheel in this diagram, perpendicular to this page), using the right hand
rule.
Angular momentum lesson
This part demonstrates the “ice skater” explanation of the conservation of angular
momentum. You will need a rotating chair. Sit on the chair with your arms close to your
body and have your lab partner slowly spin you around until you are rotating at a constant
angular speed () and angular momentum. Extend your arms and bring them in several
times to see what happens.
1) What will happen to the moment of inertia if you extend your arms outward (as far as
you can)?
2) What happens to your angular momentum if you extend your arms outward?
3) What happens to the angular velocity if you extend your arms outward?
4) Have a partner spin you around again, but also have another partner time how long it
takes to complete one complete revolution with yours arms close to your body. Without
stopping extend your arms as far as possible and repeat the timing.
: With arms close to body ________ rad/s.
: With arms out ________ rad/s.
5) Use the right hand rule to determine the direction of the angular velocity and angular
momentum. Does the direction of the angular velocity change?
6) Repeat this procedure, but this time use ~ 5 lb weights in your hand, and begin with
your arms extended. When you bring your arms, what will happen to your angular
velocity?
7- Repeat steps 4- 5 and explain your results.