Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Need Help in making a slow descending yo yo for science club presentation

  1. Dec 9, 2011 #1
    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.'

  2. jcsd
  3. Dec 9, 2011 #2
    Does it have to work like a yoyo - in other words does the entire object have to rotate and be constructed of two cylindrical sides attached by a center rod? Do you want to make it the same size as a traditional yoyo? I assume it has to fall to qualify?

    You could seriously slow it down by making a gasket to fit between the two sides to produce friction on the string as it unwinds. I'd probably use silicone sealer - the real aquarium stuff - since you can trim it and shape it

    You could also create a center movable cover and fill it with some very sticky substance - vaseline, STP oil treatment - so the string will unwind through the fluid.
  4. Dec 9, 2011 #3
    It pretty much has to unwind on the string. Does not have to look like a traditional yoyo. The dimensions are max of 20 cm each way. The rules are that no friction can be applied. The solution has to deal solely with torque and angular momentum
  5. Dec 9, 2011 #4
    yoyos already have friction so I would assume the rules mean no unusual friction. Can you fill the two sides with a fluid?
  6. Dec 9, 2011 #5
    Yes that was what i was thinking. What do u have in mind?
  7. Dec 9, 2011 #6
    I'd try a bunch of different things from a lead rim, bb's to STP oil treatment,water, ice water slush, hamsters in a wheel??? hahaha
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook