The coin rotates inside the balloon because of centrifugal force. Centrifugal force is the outward force that draws a rotating body away from the center of rotation. It is caused by the inertia (resistance to motion, action, or change) of the body. The force is often used to describe the motions of objects in a rotating frame.
Mess Kits are single-serving experiments that allow kids to explore scientific concepts at their own pace. Visitors are encouraged to complete as many as they want! See all Mess Kits.