So for my curriculum I have to do a physics experiment and write a 2000 word essay on it. For my experiment, I'm planning to wrap a string with a ball attached to it n number of times around a pole and measure the time taken for it to unwind by changing variables such as the radius of the pole, the length of the string, the mass of the ball, the angle etc. I suggested this to my teacher and he said "Go ahead, but you have to figure out a way to control the force pulling, then you'll be fine." What does he mean by the force pulling? Also, how any suggestions on how I should control it?