Why does sandpaper get hot when it is rubbed against rusty metal?

When you turn on a battery-operated device, an electrical circuit is

Free runners jump long distances and land on the ground or a wall. how do they apply newton’s second law to lessen the force of impact?

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.