Change from day to night results from the earth rotating on its axis, change from a calm day to one that is windy results from moving air, and the change of a marble's location results from the marble rolling down the ramp and across a floor. Pushing moves a stalled car, a running engine propels an emergency vehicle, applying brakes slows or stops a moving school bus, and releasing a marble from a ramp rolls it down the ramp. Click here to find out more about motion. Friction Friction is a force that interferes with the movement of one object rolling or sliding over another. It pushes in the direction opposite to which the object is moving.
Friction has many causes.
One important cause is the roughness of the rolling or sliding surface. Rough surfaces have tiny projecting irregularities. These interlock as one surface rolls or slides over another and resists motion. Smoothing the surfaces can reduce friction. Click here to find out more about friction.