The motion of an object will change when it is acted on by someforce. This force will speed it up, slow it down, change itsdirection of motion or perhaps cause it to spin. All thses changesof motion are response to the force acting on the object. This isNewton's first law: An object in motion will continue in motion(and in the same direction) unless acted on by some force. Somemight call this the law of inertia.