For an observer looking at a small ball in an inertial reference frame (IRF) which of the following statements is true? (circle the correct ones).
1) If there are no forces acting on the ball, it will not accelerate.
2) If the ball is not accelerating, there are no forces acting on it.
3) The motion of the ball is always in the direction of the net force.
4) If the ball is moving, there must be a net force acting upon it.