When a rocket falls to earth, what is the force that opposes gravity?
I sense some confusion here about what Issac Newton meant when he said, “equal and opposite reaction.” In Newton’s publications, “action” and “reaction” both mean nothing more or less than what we call “force.” When he said that “every action has an equal and opposite reaction,” that was his way of saying that forces always act BETWEEN objects. When you push on a wall, the wall pushes back on you just as hard. When a rocket feels the pull of Earth’s gravity, the Earth feels the equal and opposite pull of the rocket’s gravity. (The Earth doesn’t move as far as the rocket moves because the Earth has somewhat more mass.) Newton said that forces always come in pairs, but that’s not the same thing as saying that forces are always balanced. They’re not always balanced. If you had asked, what opposes gravity when the rocket falls toward the Moon, then the answer would be “nothing.” When forces are unbalanced, then something must accelerate (e.g., the rocket accelerating toward the moon, and t
