Hey everyone! I am trying to lead a science project for my science club and I found this great one online. Basically, students must make a yo-yo that takes the longest amount of time to descend 2.0 meters. Any pulleys, gears, mechanical friction, or air resistance may not play a part in the slowed descent. Now my problem is that I am trying to design a yo yo that would wow the observers after their project bit is over. I have thought of two ways to approach this project: 1) maximize rotational inertia 2) create a counter torque to that of that induced by the string. I am planning to combine both ideas by 1) connection two hollow cylinders (have the highest moment of Inertia) with a much thinner axle. The second is what I need help with. I need to induce a counter torque. I have thought of two ways, either using water that flows in a tube that surrounds the rims of the cylinders or using magnets. The only problem is how to induce water flow in a specific direction. If the string is making the system spin clockwise, how would i induce some sort of water flow counterclockwise? Please help me! Also, I wasn't sure where to post this so please help me redirect it to the appropriate location.' Thanks!