Is Newton's third law always correct?

Question

Newton's third law states that every force has an equal and opposite reaction. But this doesn't seem like the case in the following scenario: For example, a person punches a wall and the wall breaks. The wall wasn't able to withstand the force, nor provide equal force in opposite direction to stop the punch. If the force was indeed equal, wouldn't the punch not break the wall? I.e., like punching concrete, you'll just hurt your hand. Doesn't this mean Newton's third law is wrong in these cases?

Answer 1

The key here is that the 3rd law applies at each instant of time.

Imagine hitting a speck of dirt to get it off of a table. Hit it as hard as you like and you might never feel the Newtonian reactive force. This is because the particle accelerates so quickly that the force is only there for a small fraction of a second.

The previous answer discusses the opposite extreme: Push on a very heavy object, and the reactive force will be there for a long time

Answer 2

This is a good question! Sometimes it is hard to see how Newton's Laws are playing out, but upon deeper study, they always appear to be (as far as we can tell). Let us consider this case of punching a wall and the wall breaking:

Newton's Third Law is that "for every action, there is an equal and opposite reaction." This is sometimes rephrased with the word "force" inserted for action, which works fine, too.

This is probably easiest to understand if we just place a fist or open hand against the wall and begin to push (this makes it a static problem instead of a dynamic problem). At the point where the hand and wall meet, the hand is pushing against the wall and the wall back against the hand with equal amounts of force. If we increase the amount of force being applied with the hand, the countering force from the wall will increase proportionally.

This continues until the forces are great enough that something breaks, at which time one of the structures -- either the wall or hand -- will no longer be able to support the forces in play and collapses.

The case of punching or hitting a wall is (or seems) more complicated because we have a moving fist, so there are some momentum, kinetic energy, and related issues to take into account, but if we were able to slow it down the process is very similar to the above. Also, we need to keep in mind that the person punching or pushing on the wall is exerting sideways, friction-based force on the floor via his feet. The floor is countering this. This forces gets transferred through the house structure down to the earth. The wall will have the same going on, with the forces translating through the structure down to the earth (where they ultimately cancel out).