Date: Thu Oct 29 23:13:11 2009 ** **Back to Contents ** ------------------------------------------------------------------------ **

Author: Paul Lulai

Subject: Re: centripetal acceleration and friction demonstration

Post:

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Should mass matter? I don't think mass matters. Isn't friction the only =
force in the horizontal plane?
f=3DuN=3Dma
umg=3Dma
m's can be cancled.
=20
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Paul Lulai
Physics Teacher
US First Robotics Teacher
..:: Medtronic - St Anthony RoboHuskie 2574 ::..
3303 33rd Ave NE
St. Anthony Village Senior High
Saint Anthony Village, MN 55418
(w) 612-706-1144
(fax) 612-706-1020
plulai@stanthony.k12.mn.us
http://www.robohuskie.com =20
http://prettygoodphysics.wikispaces.com =
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=
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http://www.stanthony.k12.mn.us/hsscience/ =
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________________________________

From: tap-l-owner@lists.ncsu.edu on behalf of Andrew Morrison
Sent: Thu 10/29/2009 9:30 PM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] centripetal acceleration and friction demonstration

Do you get the different masses at the same radii to fly off at the
same time? I did it three times, and each time had a different
result: once the large mass came off first, then they both came off at
the same time, then the small mass came off first. I need to perfect
my technique, I guess.

On Thu, Oct 29, 2009 at 8:39 PM, Anthony Lapinski
wrote:
> This is a great demo! I use a lazy susan, which you can get cheaply at
> IKEA and other places. You can do the same masses (coins, washers) at
> different radii, or different masses at the same radius. Rotate the
> platform. Compare angular speed and linear speed. Then centripetal
> acceleration and centripetal force. Static friction, etc. Relate this =
to
> the Earth spinning, centripetal acceleration, apparent weight (equator =
vs
> poles), etc.
>
> tap-l@lists.ncsu.edu writes:
>>Ah...center of moment...right. Yeah, I think stacking a few pennies
>>and gluing together might do the trick.
>>
>>I'm starting to think this might be a demo that really isn't done all
>>that often.
>>
>>On Thu, Oct 29, 2009 at 6:29 PM, Bernard Cleyet
>> wrote:
>>> I'll leap in where others have refused to tread -- I think you've =
got
>>it;
>>> having the moments at the same radii is most important.
>>>
>>> bc not an angel
>>>
>>> p.s. Note: The centre of mass is not the same as the center of =
moment.
>>> Would using varying numbers of same coins stacked (glued together)
>>solve
>>> this?
>>>
>>>
>>>
>>> On 2009, Oct 29, , at 15:23, Andrew Morrison wrote:
>>>
>>>> I wanted to do a demonstration in class where two objects of =
different
>>>> mass are placed on a rotating disk at the same radius to show =
whether
>>>> one will fall off before the other or if they fall off at the same
>>>> time.
>>>>
>>>> After multiple trials, first with a dime and a quarter then with =
other
>>>> various objects, I am pretty sure I can convince my class that any =
of
>>>> the three possibilities is correct. Does anyone have a method or
>>>> suggestions of techniques for consistent and accurate ways of
>>>> repeating this demonstration?
>>>>
>>>> It seems to me that the two objects would need to have the same
>>>> material in contact with the surface, to have the same coefficient =
of
>>>> friction, and would need to have the same dimensions, so the center =
of
>>>> mass of each is in the same spot. Is that right, or am I =
overthinking
>>>> this demo?
>>>>
>>>> Thanks!
>>>>
>>>> Andrew
>>>>
>>>
>>>
>>
>
>
>

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