Newton’s laws:Relations between motions of bodies and the forces actingon them. Newton’s first law:Abody at rest remains at rest,and a body in motion remains in motion at the same velocity in a straightpath when the net force acting on it is zero. Therefore, a body tends to preserveits state of inertia. Newton’s second law:The acceleration ofa body is proportional to the net force acting on it and is inversely proportionalto its mass. Newton’s third law:When a body exerts a forceon a second body, the second body exerts an equal and opposite force onthe first. Therefore, the direction of an exposed reaction force depends onthe body taken as the system.