Hi. I am doing an experiment on golf balls. I know that the dimples are supposed to reduce the resistance when travelling through the air. I am testing the effects that dimples have on rolling resistance when on the ground. I am using 3 golf balls of the same type/brand. One, I am keeping it how it came (new, with dimples). The second I have filed HALF of the dimples off (then sanded that half to make it smooth). The third I have filed all the dimples off and sanded it to make it smooth. I have constructed a pendulum with a sinker on the end so that I can pull it back a set distance so it should hit the ball with the same force every time. This will keep the experiment controlled (every single time the ball should have the same initial velocity - I think...). I am going to conduct the experiment on a smooth concrete surface. The only things I can think of to measure is: 1. The time to taken to stop rolling 2. The distance travelled. I am stuck on how to prove the friction part of things. Like, what formulas should I use?? i know the formula: Friction force = coefficient of friction x normal force except i dont know how to find the coefficient of friction.