D3-33
To illustrate centripetal acceleration and the associated forces

A rope is tied to a tennis ball at one end, and to a brick at the other. The rope runs loosely through a plastic handle, allowing it to slide freely.

Spin the ball on its rope around in a circle above your head. As the radius of rotation increases, the centripetal acceleration does as well, increasing the force acting on the brick. At a certain point, the force will be sufficient to lift the brick off the table!

Check out further discussion of this demonstration, and a full mathematical treatment, at the link below!
D3