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Impossiball

This ball is comprised of two hemispherical halves of different density. Students will agree that this is why it has the unusual bouncing behavior.  But why does that make a difference?  So what!  


It is important to understand that the normal force on the ball need not be through the center of mass.  When the center of mass is not directly above the normal force, there is a torque on the ball that produces  rotational response on contact.