Hello! I've just begun attempting to teach myself physics, and I'm finding it difficult to understand Newton's third law. Would someone be so kind as to shed a little light on the situation? The idea of the equal and opposite reaction for every action makes perfect sense to me in some cases (a swimmer's motions push the water behind them, and in response, the water pushes them forward; I lean against a wall, the wall is pushed away from me and responds by exerting a force in the opposite direction that holds me up), however, I keep running into situations where it doesn't seem to make sense. For instance: 1) I kick a pebble and a boulder with the exact same force. My foot experiences almost no noticeable response when I kick the pebble, but when I kick the boulder, I hurt my foot. How can these both be equal reactions? 2) In outer space, a rocket is attached (by a cord, or by a beam, or by whatever would make this example logical without complicating things) to some object, let's say a crate. The rocket is trying to pull the crate. If the rocket fires, the action-reaction pair between the rocket's exhaust and the rocket subjects the rocket to some force x. Since the rocket is attached to the crate, the rocket also applies force x to the crate. Since the crate is attached to the rocket, it applies a force to slow the rocket down - which, by Newton's third law, is -x. The net force on the rocket is x - x = 0, and so, no matter how hard the rocket fires, it's never going to be able to escape equilibrium. Where's the error here? I would really appreciate help understanding where I'm going wrong with this law Thanks!