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Overview:
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- The third laws of motion deals with forces exerted by two objects on each other. When one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first object.
- These forces, termed action and reaction forces, always act on different objects.
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Football Example:
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- In football, when players collide, each feels the impact because they exert forces on each other. This interaction results in a pair of forces, not just one.
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Spring Balance Experiment:
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- Using two spring balances connected together, if a force is applied to one balance, both show identical readings, but in opposite directions.
- Third Law Principle: This illustrates the third law as the force exerted by one balance on the other is equaled by the opposing force of the second balance on the first.
 [Action and reaction forces are equal and opposite]
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Alternative Statement:
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- This provides an alternative statement for the third law: “To every action, there is an equal and opposite reaction.”
- However, these forces act on two different objects.
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Walking Example:
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- When someone tries to walk, they push the ground backwards.
- In return, the ground exerts an equal and opposite force forwards, propelling the person in the desired direction.
 [A stone describing a circular path with a velocity of constant magnitude]
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Acceleration & Mass:
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- While action and reaction forces are equal, they may not produce equal accelerations if the objects have different masses.
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Gun and Bullet Example:
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- When firing a gun, the gun exerts a force propelling the bullet forward.
- The bullet exerts an equal force backward on the gun, resulting in the gun’s recoil.
- The gun, being much heavier than the bullet, has less acceleration than the bullet despite the forces being equal.
 [A forward force on the bullet and recoil of the gun]
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Sailor and Boat Example:
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- If a sailor jumps forward from a rowing boat, the boat moves backward.
- The forward force exerted by the sailor on the water or ground is countered by an equal backward force exerted by the water or ground on the boat.
 [As the sailor jumps in forward direction, the boat moves backwards]
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