1. The problem statement, all variables and given/known data hey, i was looking at an explanation in a text book where it says a ball on the end of a string is swung horizontally in circular motion. There is a centripetal acceleration therefore tension acts as the centripetal force and acts along the radius of the circular path. What i want to know is that newtons third law states that every action has an opposite and equal reaction. So what is the reaction force of the tension acting on the string? 2. Relevant equations F=mv^2/r 3. The attempt at a solution I can't seem to be able to figure out what it is but i think mass would not be the reaction force because mass is a scaler and has no direction. The other explanation would be centrifugal force but isn't centrifugal force a reaction force of centripetal force? which is what im trying to find? This is why im a little confused.