# A Spacewalking Puzzle

Discussion in 'After Hours Lounge (Off Topic)' started by BrianW, Aug 16, 2005.

1. ### BrianW Cinematographer

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With the successful landing of the Discovery and her crew, I wanted to reflect on NASA's successful test flight. How better to do this than to successfully execute an EVA mission of our own?

Given: You are in a space suit, orbiting the Earth outside of Discovery. You are untethered, unpowered (no rockets, hair spray, or tennis balls to throw), and otherwise floating free. The only piece of equipment you have, other than your EVA suit, is a bicycle wheel. (Yes, a bicycle wheel.) Neither you nor the bicycle wheel is spinning on any axis at the start of the mission.

Mission: Your mission is to set the bicycle wheel spinning about its own axis without putting yourself into a spin.

Can you do it? Remember, it's just you and the bicycle wheel. There's no robotic arm to help, and you're not allowed to rip a hole in your suit to alter your momentum. (Though you may, if you wish, consider yourself expendable for the purposes of accomplishing this very critical mission.)

Any volunteers for this mission?

2. ### Morgan Jolley Lead Actor

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Couldn't you throw yourself while holding part of the wheel so that you go off in a straight direction and the wheel spins in the direction opposite of where you're going? You wouldn't be spinning, but you'd be moving.

You----- bicycle wheel spin

3. ### BrianW Cinematographer

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Well, shoot! That didn't last very long!

Man, my threads are the pits. :b

4. ### Morgan Jolley Lead Actor

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You just need to make sure someone who isn't in college and majoring in an engineering field (optics, specifically, but there's lots of physics involved).

5. ### Ted Lee Lead Actor

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i still don't get morgan's answer...? :b

6. ### Scott McGillivray Supporting Actor

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What is this "wheel" thingy you speak of?

Sounds promising!

7. ### BrianW Cinematographer

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Morgan's suggestion could be implemented by applying a tangential force to the rim of the wheel while ensuring that the applied force goes through your own center of mass. You must, however, let go of the wheel after you apply this force in order for it to keep spinning. In doing this, you'll apply a translation force to yourself, causing you and the wheel to move away from each other unrecoverably, but only the wheel (and not you) will be spinning. (And, indeed, the spinning wheel will completely counteract the angular momentum of the wheel's off-CM-radial-axis translation, resulting in a total zero angular momentum gain for the wheel-Morgan system.)

Morgan's really smart. (I bet his threads don't suck.)

So, has anyone read any good books lately?