Newton's 3rd Law -- action/reaction pairs 1. The problem statement, all variables and given/known data I'm a high school physics teacher and the following was a question on a work sheet. I don't really like the question and I'm not certain the the answer is correct. "A ball hangs from a string being pulled down by gravity. If the action force is Earth’s gravity pull on the ball, the reaction force (Newton’s third law force) is a. the string force on the ball. b. the ball force on the string. c. the force holding the string from above. d. the ball’s gravity pull on the Earth." 2. Relevant equations The key says the answer is D. We haven't covered Universal Gravitation yet and I don't really see it as relevant because the ball isn't levitating. 3. The attempt at a solution I'm more inclined to say the answer is the tension on the string or the force on what ever the string is tied. Am I missing something or is this just a bad question? Thanks.