This is a good start to thinking about fight physics, another thing from physics that you have to think about while training are Newton's laws of motion. The third comes up a lot for a strike.

If two bodies exert forces on each other, these forces have the same magnitude but opposite directions.

So I need my body to be a wall at the moment of impact, any give in me is less force that they have to take. So if I throw a hook, and do it with just my arm, and my feet arent set, my core and ass arent fully engaged and/or my legs are wobbly, then Im going to move and that will lessen the impact on my opponent.