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Two objects go in against each other, and then they collide, will object 1, exerting force 1, necessarily get on it a reaction equal in magnitude and opposite in direction?

EDIT:- In my book it only says "for every action there is always opposed an equal reaction". But after reading on Newton's third law on Wikipedia, I read this "The action and the reaction are simultaneous"; it's not an intuitive statement (it sounds more like an object gets a reaction after an action), but anyway that solves my problem. If you care to explain how the two forces are always simultaneous please do.

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2 Answers 2

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It sounds like you may have been confused because intuitively, you would think a reaction occurs after the action, in response to it. As you've found, that is not what Newton's third law is saying. The reaction force is not a response to the action. For this reason, some people don't like the statement "For every action, there is an equal and opposite reaction."

A better statement of Newton's third law is to say that forces always occur in pairs. It is impossible for object A to exert a force on object B without object B also exerting a force on object A. The two forces are simultaneous, of equal magnitude, and in opposite directions.

Mathematically, this is stated as

$$\mathbf{F}_{AB} = -\mathbf{F}_{BA}$$

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In Newtonian mechanics, yes. This is Newton's third law, as Chris Gerig pointed out in the comments.

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