Q4.7 As a man takes a step, the action is the force his foot exerts on the Earth; the reaction is the force of the
Earth on his foot. In the second case, the action is the force exerted on the girl's back by the snowball;
the reaction is the force exerted on the snowball by the girl's back. The third action is the force of the
glove on the ball; the reaction is the force of the ball on the glove. The fourth action is the force exerted
on the window by the air molecules; the reaction is the force on the air molecules exerted by the
window.
Q4.9 The molecules of the floor resist the ball on impact and push the ball back, upward. The actual force
acting is due to the forces between molecules that allow the floor to keep its integrity and to prevent
the ball from passing through. Notice that for a ball passing through a window, the molecular forces
weren’t strong enough.
Problems
