How is a baseball being hit demonstrating energy? Or a football being thrown?

What is the coefficient of kinetic friction μk between the block and the tabletop?

The electric potential v is constant everywhere within a certain region of space. which statement below is true? the choices are: the electric field is also constant (but not zero) within the region. a charged particle placed within the region will experience an electric force. the electric field is zero everywhere within the region. the electric field varies from place to place within the region.

If you put a helium-filled balloon in the refrigerator, what will happen?