That's How I Roll - a thread in the Got Homework? forum

The Nucleus » Nucleus Discussion Forums » Forum » Thread » Post and Replies

That's How I Roll post and replies

Return to the That's How I Roll thread
Login to post to this thread

Where are the solutions? - Oct 26, 2007 at 9:19AM
Dave San Marcos, Texas 308 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 Login to reply

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. NSF Program Director (on assignment from the AIP and the Society of Physics Students to serve as the Robert Noyce Scholarship Program Director at the National Science Foundation) Login to reply \| Condense

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.

NSF Program Director (on assignment from the AIP and the Society of Physics Students to serve as the Robert Noyce Scholarship Program Director at the National Science Foundation)

Login to reply | Condense

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: basketball ~ 2/3(MR^2) 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)MV^2 + (1/2)Iw^2 + MgH = constant and with V=Rw 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. NSF Program Director (on assignment from the AIP and the Society of Physics Students to serve as the Robert Noyce Scholarship Program Director at the National Science Foundation) Login to reply \| Condense

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:
basketball ~ 2/3*(MR^2)
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.

NSF Program Director (on assignment from the AIP and the Society of Physics Students to serve as the Robert Noyce Scholarship Program Director at the National Science Foundation)

Login to reply | Condense