Newton's Third Law of Motion: Definition, Examples, and Applications

Newton's Third Law of Motion

Newton's Third Law of Motion is one of the most well-known principles in physics. It states:

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

This means that forces always occur in pairs. When one object exerts a force on another, the second object exerts an equal force in the opposite direction on the first. These forces are equal in magnitude but opposite in direction, and they act on different objects.

Real-World Examples

• Walking: As your foot presses backward against the ground, the ground responds by propelling you forward.
• Swimming: Your hands push water backward, and water pushes you forward.
• Rocket Launch: Hot gases push downward, and the rocket moves upward.

Mathematical Understanding

While Newton's Third Law does not have a direct formula like the Second Law, it is closely related to force calculations. If an object A exerts a force F on object B, then object B exerts a force of −F on object A:

F_AB = -F_BA

Key Points to Remember

• Forces always come in pairs - action and reaction.
• The forces act on different objects, so they do not cancel each other.
• Both forces are equal in size and opposite in direction.

Newton's Third Law is essential in understanding motion, propulsion systems, and many engineering designs, from vehicles to sports equipment.