A disc and a ring with the same mass and diameter have a race!
WATCH THE VIDEO
Teachable Topics:
- Newton's Laws
- Rotational Motion
- Moment of Inertia
Theory:
How fast an object will roll down a hill depends on not just the angle of the hill, but the manner in which the mass of the object is arranged around its centre of rotation.
The mass distribution is quantified by the Moment of Inertia. A solid disc and a ring will have very different moments of inertia due to the fact that the ring has all of its mass concentrated away from its center while the disc mass sone of its mass closer in. Conservation of angular momentum predicts that it will be harder to accelerate mass father away from the centre than that closer in.
In a race between the disc and ring of equal masses, it should be the disc (with the lower moment of inertia) that will win!
Apparatus:
- Disk and Ring of equal mass and diameter
- inclined plane
- stopwatch (optional)
- small ruler of meter stick to make it easier to start the race (optional)
Procedure:
- Ensure the inclined plane is clean and clear of all debris. The angle of incline should be more than 10 degrees.
- If desired, measure out a set distance between the start and finish.
- Set up both object at the starting point.
- Release the objects so they are free to roll down the plane. Observe which arrives at the end first!
