1. The problem statement, all variables and given/known data A particle moving along a straight line can have nonzero acceleration even when its speed is zero (for instance, a ball in free fall at the top of its path). Can a particle moving in a circle have nonzero centripetal acceleration when its speed is zero? If so, give an example. If not, why not? 2. Relevant equations 3. The attempt at a solution I think the answer is no...after all, so something to be experiencing centripetal acceleration, it needs to be moving in a circle. Everything wants to just move in straight lines, but if there's friction on tyres or tension in a string, then that becomes a centripetal force giving centripetal acceleration, but that tension or friction can't exist without motion in the first place...am I right? Wrong? What's going on here? It's says zero speed...if you're speed is zero, then you can't have direction can you?