This is probably an elementary question, but I am trying to help my nephew answer a worry. His question is: given Newton's third law, when a ball is thrown up in the air, we would push the earth a little downward. But whatever acceleration imparted and distance traveled during the throw the earth moved, why don't we have to take this into consideration?
I know from experience it is because we assume the earth didn't move. But I want to give him a better reason. I think the following, can someone confirm it is right we can assume it doesn't move because:
- There are thousands of things happening at once, therefore all these actions/reactions tend to cancel out.
- Earth is too massive to make a difference.
- Our force might only compress part of earth, not earth as a whole.
- Even if it did move or accelerate when the ball was thrown, when they collide as it comes back to ground, technically each would stop one another.
Therefore, we can safely ignore in all practical problems. This correct? Darn it, should have kept my highschool physics book given all this remote learning.