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# If action is always equal to the reaction, explain how a horse can pull a cart?

A horse pushes the ground in a backward direction. According to Newton’s third law of motion, a reaction force is exerted on the horse in the forward direction. When the horse walks in the forward direction (with the cart attached to it), it exerts a force in the backward direction on the Earth. An equal force in the opposite direction (forward direction) is applied on the horse by the Earth. This force moves the horse and the cart forward. As a result, the cart moves forward.

## Newton’s third law of motion

Newton’s third law of motion states that when one body exerts a force on the other body, the first body experiences a force equal in magnitude in the opposite direction of the force exerted.

### Applications of Newton’s Third Law of Motion

• A gun recoils when a bullet is fired from it: When a bullet is fired from a gun, the gun exerts a force on the bullet in the forward direction. This is the action force. The bullet also exerts an equal force on the gun in the backward direction. This is the reaction force.
• A person is moving forward during swimming