huh, is it kinda fittin', huh? the moon and the earth are pulling on each other in one interaction. and that one interaction, earth pull on moon, moon pull on the-- you can't have one without the other. they're both counterparts of the same interaction, do you see that? we can out that down as a rule. if body "a" pulls on body b, call that action. and the reaction is body b pulls on body "a." it's that simple. let's put that up here. if action is "a" pulls on b, "a" could be the earth. the earth pulls on the moon. how can that be? unless... okay? and we call that the reaction. reaction is just--flip-- switch 'em around. b pulls on "a." it's that simple. you got it? i wanna move across the floor. what i do is i push back on the floor. i push back on the floor with feet. i'm pushing the floor this way. if i'm on a skateboard, just see it move that way, huh. i push back on the floor. what pushes on me? - floor. - the floor. if i push back on the floor, honey, the other part of the interaction is the floor push-- that's why i move. you're in a swimming pool. you're here. you wanna get t