Newtons First Law

Newton’s first law states that a resultant force is required for an object to start moving, speed up or slow down. This means that without a resultant force, an object’s motion will not change.

This principle applies to both stationary and moving objects.

  • If the resultant force on a stationary object is zero, then the object remains stationary
  • If the resultant force on a moving object is zero, then it will carry on moving at the same velocity. – This means that it will keep travelling at the same speed and in the same direction.

The resultant force is the overall force acting on an object. In both cases, there is no resultant force acting on the objects, so their motion will not change.


1. The boulder is stationary because it has no forces acting on it.

2. Balanced forces act on the boulder, so it remains stationary. The two men pushing the boulder from opposite sites create the forces.

3. Unbalanced forces act on the boulder, which means the resultant force is not zero, so the boulder accelerates.


1. The ball is stationary because no forces are acting on it.

2. Unbalanced forces from the foot act on the ball. So the ball accelerates.

3. The ball is in motion, so it stays in motion.

4. Unbalanced forces from the net act on the ball. So the ball changes speed and direction, slowing down.