Physics Tutorial: Newton's Third Law; Flight

Physics Tutorial: Newton's Third Law and Flight

Newton's Third Law of Motion: For every action, there is an equal and opposite reaction. This statement means that in every interaction, there are two forces acting on the interacting objects. The size of the force on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object.

Newton's Third Law of Motion benefits us every day.

The flying motion of birds is a good example of the Newton's third law. The wings push the air downwards.

In turn the air reacts by pushing the wings (and therefore the bird) upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air which is downwards is opposite the direction of the force on the bird which is upward. For every action, there is an equal and opposite reaction.

Question: While driving a car on the highway you hit a bug. The bug hit the windshield and the windshield hit the bug. Which of the two forces is greater? The force on the bug or the force on the windshield?

Answer: This is a trick question. Each force is the same size since Newton's third law states for every action there is an equal reaction. Because the bug has less mass, its motion is effected more by the force - but that is another law.

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Ahsan Farooqui