EXPORING TOPS

Some excellent links:

I didn't know that tops had such a noble history. Here is a web site that could only have been made by someone who loves tops (check out the other page about yoyos, too). http://www.spintastics.com/HistoryofTop.asp

I hunger for an intuitive understanding of the science in the world around me. Precession--the effect that makes tops and gyroscopes behave as they do--is so counterintuitive that it almost seems like you would have to study magic to understand it.

Take the common physics demonstration with a bicycle wheel that is both very easy to do and very weird. The front wheel of a bicycle is easy to take off (but don't do it unless you're sure you can get it on straight again). Tie a string to one end of the axle. Spin the wheel very fast while it is vertical (this is much easier to do with two people). Then hold the spinning wheel by the string. IMPOSSIBLE! It retains its vertical position and slowly circles around the string. It seems to defy physics, but it is physics. Specifically, that's precession.

Taking off the string, you can hold the fast-spinning wheel by the axles. Turn in gently one way, but it actually turns 90 degrees to what you intended. It's almost as if ghost hands are intervening. Many science museums allow you to do a closely related activity on a spinning chair.

Fun, but why does it do that? If you have a rudimentary understanding of momentum (objects in motion tend to stay in motion) and are OK with the concept of directional force (as in a push), you might be able to really understand the following explanation of precession. It comes from HowStuffWorks, which is a really fun web site to wander in. The explanation is in two parts: how a side-way push on a section of a wheel keeps acting even when the section rotates to new position, because of momentum. And, secondly, how the force in the direction you meant to push the wheel is canceled out by an opposite force. If you take the time to read the explanation, tinker, and re-read the sentences, you might get it. Willing to have a go of it? Click on http://www.howstuffworks.com/gyroscope2.htm

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