I read all the previous answers concerning the 3rd law and I have seen that it is definitely not universal, (Edit: but conservation of momentum is. If it is not universal it should be not a problem to exclude also gravity.)
Newton derived his law from the collisions in a primitive 'cradle'. Why do physicists strive to make that statement universally applicable? It seems generally agreed that it is a consequence of the conservation of momentum in collisions. What is the conceptual or practical necessity to extend this principle to situations where it is not applicable? Conservation of momentum is a universal law, but that does not imply that action must be always equal to reaction, which as a matter of fact does not happen.
- 1) any body can offer a max resistance due to its mass (oterwise called 'inertia') = k (reaction), any action on it which is < k will get an adequate reaction, but any action which is > k will obviously not get a sufficient reaction. If a ball hits a wall with p > k the wall will crumble.
- 2) can an object provide a reaction if the object never gets in contact with it?
Update: The answers, do not answer my question:
They did do just that from the 17th century to the 19th century, but that is no longer the case.
I was not referring to 19th century but to today's phisicists:
Alba,you don't quite understand Newton's laws of motion.... Newton's third law is about forces. - David Hammen
If 3rd law is about forces and not momenta*, please explain how it works when a skater is pushing at the rail or at a basketball: the reaction id different: The action in both cases does 210 J of work, but the reaction is different, what is equal is only the momenta. Please show how you get equal actions and reaction considering forces.
... ..Saying the third law should imply equal forces in any arbitrary pair of scenarios seems obviously nonsensical – Hypnosifl
Can someone please tell me if this is true? According to 3rd law, If I exert a force of k N on 10 different bodies, shouldn't I expect the same reaction of k N from all the 10 different bodies? If the reaction (force) of the rail and of the ball is the same, how can the same force produce a velocity times greater in the second case?
I have not changed the above discussion as it is necessary to unterstand the old answers. But it is now obsolete.
Bounty question
Consider a man in vacuum or frictionless environment pushing (F = kN) at one object (stone, ball etc.) with one hand or at two objects with two hands in opposite direction, show:
1) that the object(s) exerts an equal reaction (F = kN) and it is a force and not a (change of) momentum
2) that the same force exterted on an object of different mass provokes the same reaction .
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