For simple experiments, you can simply use your hand. For more complex experiments, you can use the Ultra Pulley (included with the CFA) and a string. The Ultra Pulley mounts on the preinstalled Ultra Pulley Bracket on the left side of the frame of the CFA. Attach one end of the string to the 3-Step Pulley mounted on the Rotational Shaft of the CFA. Attach a small mass to the other end of the string. Run the string over the Ultra Pulley and allow it to fall to apply a torque to the Rotational Shaft.