Re: Newton's 3rd law is wrong

Moderator 28/09/2024 13:19:13 ha scritto:

[[Mod. note -- As I explained in a moderator's note on 2024-Sep-16, you're misunderstanding what Newton's 3rd law says.  Newton's 3rd law says that  (1) The force the rope applies to the stone is equal in magnitude and     opposite in direction to the force the stone applies to the rope,    AND (2) the force the horse applies to the rope is equal in magnitude and    opposite in direction to the force the rope applies to the horse.

This is why the third law error has never been discovered.

Because we trusted action separated from reaction, as if action could act here and reaction (independently) there.

But no, action always fights against reaction and tries to make its own reasons prevail over those of the other.

The action of one body does not go against another body but against the reaction of the other body and vice versa.

The difference is fundamental because in an indirect clash there is never a winner, while in a direct clash there is (usually) a winner.

In a direct clash with reaction, action wins if it is stronger and loses if it is weaker.

But as usual, I can express myself better with an example taken from real life.

We have to build a road but there is a large stone that is in the way and, therefore, we have to find a way to move it.

Let's take a thick rope, tie one end to the horse and the other to point P of the stone.

Our idea is that, if we can move point P of the stone, we will also be able to move the entire stone.

We encourage the horse to move, it pulls the rope and the rope pulls point P which does not move.

What happened? What happened is that (at point P) the force coming from the horse (which is equal to +8) is not enough because the friction of the stone can only be overcome with a force greater than +10.

The horse does not make it and its action +8 on point P is cancelled out by the reaction -8 of the rest of the stone (always on point P) and point P does not move, just as neither the horse nor the stone move.

There are no net forces, there are no accelerations (the velocity remains equal to v=0) and the action of the horse meets a perfectly equal and opposite reaction everywhere.

Just as the third law states.

Then we replace the weak horse with a stronger pack horse that can exert a force equal to +12 and point P starts moving, that is, it accelerates from speed v=0 to speed v>0.

What happened? What happened was that, at point P, the action +12 of the horse prevailed over the reaction -10 of the rest of the stone and point P moved forward together with the whole stone!

This is how action and reaction work, with a direct clash where in the first case (with the weak horse) they tied and in the second case (with the stronger horse) the action won.

If it were as the third law states, how could we have moved the stone to build the road if at point P the rightward action of the horse was (always and in any case) equal and opposite to the leftward reaction of the rest of the stone?

It is at point P that the action of the horse and the reaction of the rest of the stone confront each other.

Luigi Fortunati