Third Law of Motion

Introduction

Many motions around us involve interaction between two bodies. When one body applies a force on another body, the second body also applies a force on the first body. This idea is explained by Newton’s Third Law of Motion.

Newton’s Third Law of Motion

Newton’s Third Law of Motion states that:

"To every action, there is an equal and opposite reaction."

This means that whenever one body exerts a force on another body, the second body exerts an equal force in the opposite direction on the first body.

Explanation

The forces in Newton’s Third Law always occur in pairs. These two forces are called action and reaction.

• They are equal in magnitude.
• They are opposite in direction.
• They act on different bodies.
• They act at the same time.

Because action and reaction act on different bodies, they do not cancel each other.

Examples from Daily Life

• When we walk, our foot pushes the ground backward and the ground pushes us forward.
• When a gun fires a bullet forward, the gun recoils backward.
• A swimmer pushes water backward, and water pushes the swimmer forward.
• When a balloon releases air backward, the balloon moves forward.

Illustration

In the figure, the person pushes the wall. At the same time, the wall pushes the person back with an equal force in the opposite direction. This shows action and reaction.

Important Points

• Action and reaction are equal and opposite.
• They always act on different bodies.
• They occur at the same time.
• They do not cancel each other because they act on different objects.
• Newton’s Third Law explains many motions in daily life.

Conclusion

Newton’s Third Law of Motion explains that forces always occur in pairs. Whenever one body applies a force on another body, the other body also applies an equal and opposite force. This law helps us understand walking, swimming, recoil of guns, and many other everyday motions.