Answer to Question #73647 in Mechanics | Relativity for himanshu

Question

hey i have a question on newton 3rd law . if every action has equal and opposite and equal reaction then when i rotate my hand in air the molecules of air should exert a equal force back to my hand and if the equal and opposite then my hand should not move through as an equal and opposite force opposing it.

Answer 1

Third Newton's Law is correct. While moving your hand in air , your hand acts on
molecules of air with some force. This force acts on molecules, not your hand. It is true that you
receive equal force back to your hand due to Third Newton's Law. This force acts on your hand.
(Often we call it air resistance). This is not correct to add these two force and say that they cancel each other, because these two forces acts on different bodies, the first one on molecules of air while the second one on hand.
You may ask: why hand is moving?
Because there is another force: you body acts on you hand. This force may be greater then air resistance.