Tuesday, 16 July 2013 12:57

## D3-03 ROTATING CHAIR AND WEIGHTS

• ID Code: D3-03
• Purpose: Illustrates conservation of angular momentum
• Description:
A subject, holding the weights with their arms extended, is started into rotation. When the weights are pulled inward to the chest of the subject, the moment of inertia of the system is decreased, leading to significant increase in the angular speed of the rotating chair.

Please take care when using this device, especially when accelerating. You can gain a significant increase in rotational speed, so hold on! And it is best not to have a person push the chair around very much, as it is very easy to hit them with a weight by accident.

##### Engagement Suggestions
• Consider inviting a participant from the class.
• Encourage students to predict what will happen before performing the demonstration.
• Once the demonstration has been performed, discuss the activity both in terms of angular momentum and its conservation, and in terms of kinetic energy.
• For extended discussion, introduce the idea of friction. How does friction work in this system? How does it affect the angular momentum? Where does the kinetic energy go?
##### Background
This device illustrates the conservation of angular momentum. When the heavy weights are moved closer to or farther from the axis of rotation, the distribution of mass and thus the rotational inertia (or moment of inertia) changes.

To show this in a different way, a single user with a single weight can move themself in a circle by swinging their arm wide holding the weight from front to back, then drawing it inwards before extending their arm forwards again and repeating the motion. This is essentially a rotational analogue of pumping a swing.

• Availability: Available
• Loc codes: FS0
• #### D3-01 MASSES SLIDING ON ROTATING CROSSARM

Illustrates conservation of angular momentum Read More
• #### D3-02: MASS ON STRING - ORBITS WITH VARYING RADIUS

Illustrates conservation of angular momentum Read More
• #### D3-03 ROTATING CHAIR AND WEIGHTS

Illustrates conservation of angular momentum Read More
• #### D3-04: ROTATING STOOL AND WEIGHTS

Demonstrate conservation of angular momentum. Read More
• #### D3-05 ROTATING CHAIR AND BICYCLE WHEEL

Illustrates conservation of angular momentum Read More
• #### D3-06: ROTATING CHAIR - HELICOPTER MODEL

Demonstrate conservation of angular momentum Read More
• #### D3-07: ROTATING PLATFORM

Demonstrate rotational kinematics and inertia. Read More
• #### D3-12: SWING MODEL

Model the pumping of a swing using conservation of angular momentum. Read More
• #### D3-21: INVERSE SPRINKLER - GLASS MODEL

This is a non-working sprinkler that was used for data in an American Journal of Physics paper. Read More
• #### D3-22: INVERSE SPRINKLER - METAL MODEL

Demonstrate the Feynman inverse sprinkler effect. Read More
• #### D3-31: AIR TABLE - TETHERBALL

Show qualitatively an example of non-conservation of angular momentum. Read More
• #### D3-32: KEYWHIP

Demonstrate angular momentum conservation in a surprising way. Read More
• #### D3-33: Centripetal Acceleration - Rotating Ball and Brick

Illustrate centripetal force and its relationship to velocity and radius. Read More
• #### D3-41: AIR TABLE - RECTANGULAR PUCK COLLISIONS

Qualitatively show conservation of angular momentum in collisions of a circular puck with a rectangular puck. Read More
• 1