my general question is how do you know what direction these forces point in, particularly when spinning an object on a string (either horizontally or vertically) or when say a car is driving in a circle. the first one has centripetal acceleration and tension. the 2nd example has centripetal acceleration and friction. how do you know what direction they point in? my guess is centripetal points in and the other two (friction/tension) point out but im not sure. can someone please help? thanks.