A2L Item 083
- Description: Describe the motion of a child on rotating disk after dropping a rock.
- Goal: Reasoning with dynamics.
- Source: UMPERG
- Keywords: Dynamics, Friction, Mechanics, Rotational Motion
The question for students:
A child stands on a spinning disk. Suppose that there is friction between the child’s shoes and the surface of the disk. While holding a rock the child stands at the largest radius possible for the current angular velocity without slipping. After releasing the rock, the child will…
- lose traction and slide off the disk.
- lose traction, slide towards center.
- remain on disk and able to move out.
- remain on disk, unable to move out.
Commentary for teachers:
Answer
(4) There should be no consequence of dropping the rock. Because the normal force changes, so does the friction force. The new friction force is still able to provide the necessary centripetal force for the circular motion.