According to Newton’s third law of motion, “To every action, there is an equal and opposite reaction.” This means that whenever an object interacts with any other object, there exists a pair of interaction forces acting on both objects. The third law of motion is also called the action-reaction law. Both the action and reaction forces act on the objects simultaneously. If both the forces are equal in magnitude, equilibrium is maintained, and the object does not move. In such a case, a balanced force is said to be existing. If one of the forces is greater than the other, the object is subjected to motion, and an unbalanced force exists.
1. Recoil of a Gun
The recoil of a gun is one of the best demonstrations of action-reaction forces. When a bullet is fired from a gun, the gun moves backward. The action force exerted due to firing is in a forwarding direction that causes the bullet to move ahead. The jerk felt on the gun that pulls it in the backward direction exists due to the reaction force. This is the reason why a person operating a gun takes the support of his shoulder to avoid injury.
A person swimming in a forward direction pushes the water in the backward direction with his/her hands. This force applied by the person acts as the action force, which leads to the generation of a reaction force. This pair of forces, acting together simultaneously on the person’s body and the water, causes the person to swim in the forward direction.
3. Pushing the Wall
When a person sitting on a chair pushes the wall with his feet, the chair moves backward. The motion of the chair can not exist without the existence of a force. Therefore, the force responsible to move the chair is the reaction force. The reaction force is always exerted in the direction opposite to the direction of the action force. Hence, the chair moves in a backward direction.
4. Diving off a Raft
When a person jumps out of a boat and steps on the bank, the boat moves back in the direction opposite to the direction of the jump. The force applied by the person on the rigid surface of the ground is the action force. In contrast to the action force, a reaction force gets generated that pushes the boat and causes it to move.
5. Space Shuttle
When a rocket is ignited, a series of chemical reactions take place that generate a huge amount of gases. These gases when hit the ground cause a force that helps the rocket to move upward. A similar process occurs in the jet engine. The only difference is that the rocket is required to carry an oxidizing agent because it has to enter an environment that does not contain oxygen.
6. Throwing a Ball
When a ball is thrown on the floor or a wall, it bounces back. The force exerted by the ball on the ground or wall is the action force. The force that the ground or wall exerts on the ball in response to the action force causes the ball to jump or bounce back. This force is nothing but the reaction force.
When we walk, a significant amount of force and pressure is exerted on the ground by our feet. The ground in response exerts an equal amount of force in the opposite direction. In absence of the reaction force produced by the ground, our foot sinks. Similarly, if the action force supplied by the foot of the person is significantly higher, the reaction force can help us to jump. Hence, walking is possible because a pair of action-reaction forces act on the feet and the ground.
8. Hammering a Nail
While hammering a nail in the wall, a force is felt on the person’s hand who is holding the hammer. It gets developed as a result of the force applied by the person on the nail. Both the forces are directly proportional to each other, which means with an increase in the action force, the reaction force increases.
A person jumping on a hard floor gets hurt more severely than a soft surface. This is because the weight of the person causes an action on the surface. The surface, in turn, generates a reaction force that acts in the opposite direction. The hard surface does not absorb any force and generates the same amount of force in response. On the other hand, the soft surface that is elastic in nature absorbs a significant portion of the action force and therefore, generates less reaction force.
10. Evacuating a Balloon
A balloon filled with air when released with its end untied lets out air with force. With the help of the action force that is caused due to the air rushing out of the balloon, a reaction force gets developed that causes the balloon to move upward.