That's How I Roll post and replies

Where are the solutions? - Oct 26, 2007 at 9:19AM

Dave
San Marcos, Texas
420 Posts

No one has submitted a solution to the challenge yet.  Where are all the talented physicists?

Dave

Try not to become a man of success, but rather try to become a man of value -- Albert Einstein

Replies to Where are the solutions?

can of soapy H20 beat a basketball? - Dec 11 2007 12:50PM
Gary
Society of Physics...
293 Posts

I wanted to write something about the rolling survey...most people are responding that a basketball will win the rolling contest, but I thought that I had seen a can of soapy water beat a basketball (even a bowling ball!)at my school when we did this...

the idea is that the soapy water is 'slippery' enough so that the can rolls without getting the water to spin very much, at least initially, and that for short ramps this means that the can can beat the basketball or a bowling ball...

a person on a bike (not pedalling) beat all of these though, as I recall!

Does anyone else have real experience with this?

Post edited December 11, 2007 at 12:55 PM EST.

Post edited December 11, 2007 at 12:55 PM EST.

Adjunct Professor of Physics, Editor of The Physics Teacher, and GWU SPS Chapter Advisor

Re: can of soapy H20 beat a basketball? - Dec 11 2007 12:57PM
Gary
Society of Physics...
293 Posts

By the way, even a can of catchup has a smaller inertial mass than a basketball, right? even a solid cylinder...so why is everyone answering basketball?

Comparing effective moments of inertia:
bowling ball ~ 2/5 (MR^2)
can of catchup ~ 1/2 (MR^2)
can of soapy water < 1/2 (MR^2)

Thus, conservation of energy gives
ME=(1/2)*M*V^2 + (1/2)*I*w^2 + MgH = constant
and with V=R*w we have
ME = (1/2)*(M+I/R^2)*V^2 + MgH = constant

thus the smaller the moment of inertia coefficient the faster the object has to roll

Am I missing something? why would people say that a basketball wins?

Post edited December 11, 2007 at 1:11 PM EST.

Adjunct Professor of Physics, Editor of The Physics Teacher, and GWU SPS Chapter Advisor

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