Hey everyone, I was reading my text and am kind of confused over Newton's 2nd and 3rd law. I understand them individually, but I don't understand how they are both true. My book covered a small portion on inertial frame of reference, which I didn't quite understand -- and I believe this may be key to understanding how they're both true. First, to be sure, is the inertial frame of reference on Earth always Earth? They gave an example of how someone standing on roller skates on a airplane would roll backwards once it started to accelerate, therefore stating that the plane is not a good inertial frame of reference. Which, to me, seems pretty intuitive. You'd have to take Earth as your frame of reference since your body will roll backwards to remain at rest from your initial position relative to Earth. As far as the 2nd and 3rd law, I'm confused how every action has an equal and opposite reaction if there can be a net differences in forces. In my book they said that Newton's 3rd law is what causes a rocket to lift because the ground pushes back just as much as the rocket trying to launch. But to my mind, if this is true, the rocket should just stay put because the forces should cancel out and put it into equilibrium. Obviously this isn't case from observation, but I don't really understand why, which makes me feel the rocket is more inclined to be following the 2nd law in that instance, that it's net force would be upwards, hence the lift. However, the 3rd law also makes intuitive because if there was no equal and opposite reaction things would just fall through each other. Can someone clear this up, please?