Question

Newton's third law states that every force has an equal and opposite force. Why don't these force-pairs just cancel each other out so that nothing ever accelerates?

Answer 1

Hi

I guess because those forces act on different objects so they don't cancel.
Let's say Object A push Object B, Object A applies an action force on object B then Object B applies a a reaction force on Object A and not on itself.

Net force applies on an object. What I mean is, only forces that act on an object can be cancelled. In the case of Object A and Object B, those forces acted on DIFFERENT objects so they don't get cancelled.

Answer 2

Hmmm so if we consider the force-body-diagram, then there would only be a single line resulting from the action of A? and nothing would be shown coming from B?

Answer 3

well, here's a great answer to this, courtesy of Richard Feynman.
https://www.youtube.com/watch?v=36GT2zI8lVA
see especially after 0:55

brilliant.

an alternative answer, which actually doesn't address "why" and is more along the lines of "how does classical physics explain" lies in Newton's first law and his notion of inertia. the back force is a result of the accelerating body's inertia.

but that too, ie the "desire" of a mass to stay at rest or in uniform motion, is really just an observation. who knows why? we can then go on to talk about electric charges and force fields and so on, but it still doesn't explain why.

Answer 4

\(\color{blue}{\text{Originally Posted by}}\) @lucy4104
Hmmm so if we consider the force-body-diagram, then there would only be a single line resulting from the action of A? and nothing would be shown coming from B?
\(\color{blue}{\text{End of Quote}}\)


let's see