Newton's Third Law of Motion

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that whenever an object exerts a force on another object, the second object exerts a force of equal magnitude but in the opposite direction on the first object. In simpler terms, if object A pushes or pulls on object B, object B pushes or pulls back on object A with the same force.

Explanation using a Spring Balance

A spring balance is a device used to measure the force exerted by an object. It consists of a coiled spring attached to a hook, with a scale that measures the elongation or compression of the spring. When an object is hung on the hook, the spring stretches or compresses, and the scale displays the force exerted by the object.

Applying Newton's Third Law

When an object is hung on a spring balance, several forces come into play:

1. Action Force: The object exerts a downward force due to its weight. This force is known as the action force because it is the force being applied by the object.

2. Reaction Force: According to Newton's Third Law, there is an equal and opposite reaction force exerted by the spring balance. This force is known as the reaction force because it is the force exerted in response to the action force.

3. Equilibrium: When the object is stationary and the spring balance shows zero reading, it indicates that the action force and reaction force are balanced. This is because the weight of the object is equal to the force exerted by the spring balance.

4. Reading on the Spring Balance: When the object is not in equilibrium, the spring balance displays a reading that corresponds to the force exerted by the object. This reading is equal in magnitude but opposite in direction to the force applied by the object.

5. Conservation of Momentum: Newton's Third Law also implies that the change in momentum of an object is equal and opposite to the change in momentum of the other object involved in the interaction. This principle helps explain various phenomena, such as the recoil of a gun when a bullet is fired.

In summary, the use of a spring balance demonstrates Newton's Third Law of Motion by showing how the action force exerted by an object is balanced by the reaction force exerted by the spring balance. This law helps us understand the fundamental relationship between forces in any interaction.