In a magnet an (what? ) is a pull between the north and south pole

The speed of light can be used to measure the

What is the force that opposes motion and works against the downward pull? a) friction b) gravity c) weight d) acceleration

A1-lb collar is attached to a spring and slides without friction along a circular rod in a vertical plane. the spring has an undeformed length of 5 in. and a constant k =25 lb/ft. knowing that the collar is released from being held at a determine, the speed of the collar and the normal force between the collar and the rod as the collar passes through b.