Re: pinhole friction with tires

Date view	Thread view	Subject view	Author view

From: Steven Eiger (eiger@montana.edu)
Date: Thu Jan 27 2000 - 13:56:29 PST

Next message: Paul Doherty: "Pinhole List/Ganson"
Previous message: Heidi Black: "Re: pinhole journalist seeking inspirational teachers"
In reply to: bliss: "Re: pinhole friction with tires"

Message-Id: <l03102800b4b669a2c9d3@[153.90.241.107]>
Date: Thu, 27 Jan 2000 14:56:29 -0700
From: Steven Eiger <eiger@montana.edu>
Subject: Re: pinhole friction with tires

Sarah, Rolling friction ought to be hard to compute; my guess would be to
get something with a lot of it, like a cart with tires of very low air
pressure and pull it on an absolute level surface using one of those spring
scales at a constant, low speed. The frictional forces would then be due
to rolling friction and air resistance. They both ought to increase with
speed, and I do not know a good way to get the air resistance out; perhaps
repeat experiment with very pumped up tires, and see the difference which
would be the added rolling resistance, but the speed would have to be the
same. Your question about rolling friction equaling static is interesting:
If you've got something with a lot of rolling resistance, like the gym
mats, they slide because that is easier, or putting it another way, the
rolling resistance is greater than the sliding resistance. Usually wheels
roll, because the rolling resistance is less. Of course as we drive and
hit a slick of ice sometimes we begin to slip momentarily.. the static
friction has decreased for a moment. I imagine a call to a tire company
would get some sort of values for rolling friction on their products. A
metal tire would have nearly zero rolling friction, other frictions would
depend on the nature of the two surfaces, eg. macro and microscopic
smoothness and material. bicycle racers are very aware that rolling
resistance decreases with increasing tire pressure, they can feel it. Steve

>Thanks Steve and Heidi. Things are getting clearer. Final question: is
>there a way to compute rolling friction? Is it the same as other types of
>friction, just with a different coefficient? Or is there a value for the
>deformation of the tire?
>
>Also, if a tire is not very deformable (i.e. metal tires on our dynamics
>carts), then does the rolling friction approximately equal the static
>friction?
>
>Cheers, Sarah
>
>>Sarah,
>>When you hit the brakes hard, locking up the wheels, they slide over the
>>road. This is kinetic friction. It is like sliding a block across the
>>table. It usually requires a larger force to get the block moving
>>initially, this is static friction, the force holding the block or wheel
>>static tot he surface. Rolling friction is different from these two as the
>>wheel is statically adhering to the road, yet as it rolls it deforms, this
>>deformation degrades energy. The earlier answer implied that deformable
>>objects are easier to slide than roll. obviously this is very dependent on
>>the vlaue of kinetic friction and the rolling resistance. For a tire, even
>>on a gym floor, it is much easier to roll it than to drag it. Of course,
>>it does not deform nearly as much as a rolled up gym mat as they both roll.
>>eiger
>>
>>>So from Heidi's answer I see that other people do teach the concept of
>>>rolling friction. Is rolling friction distinct from static friction though?
>>>I'm still confused. Sarah
>>>
>>>ййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййй
>>>й
>>>
>>>Sarah Wise
>>>
>>>Lick-Wilmerding H.S.
>>>755 Ocean Avenue
>>>San Francisco, CA 94112
>>>swise@lick.pvt.k12.ca.us
>>>
>>>"Not everything that can be counted counts,
>>>and not everything that counts can be counted."
>>>--Albert Einstein
>>>
>>>
>>>
>>>---------------------------------------------------------------------------
>>>To unsubscribe from pinhole, send an email to requests@exploratorium.edu
>>>with the words 'unsubscribe pinhole' (without the quotes) in the SUBJECT
>>>of the email.
>>>
>>>To subscribe to the digest and only get 1 combined message a day, send an
>>>email to requests@exploratorium.edu with the words 'subscribe digest
>>>pinhole' (without the quotes) in the SUBJECT of the email.
>>>---------------------------------------------------------------------------
>>
>>
>>Steven Eiger, Ph.D.
>>
>>Departments of Biology and the WWAMI Medical Education Program
>>Montana State University - Bozeman
>>Bozeman, MT 59717-3460
>>
>>Voice: (406) 994-5672
>>E-mail: eiger@montana.edu
>>FAX: (406) 994-3190
>>
>>
>>
>>---------------------------------------------------------------------------
>>To unsubscribe from pinhole, send an email to requests@exploratorium.edu
>>with the words 'unsubscribe pinhole' (without the quotes) in the SUBJECT of
>>the email.
>>
>>To subscribe to the digest and only get 1 combined message a day, send an
>>email to requests@exploratorium.edu with the words 'subscribe digest pinhole'
>>(without the quotes) in the SUBJECT of the email.
>>---------------------------------------------------------------------------
>
>йййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййййй
>
>Sarah Wise
>
>Lick-Wilmerding H.S.
>755 Ocean Avenue
>San Francisco, CA 94112
>swise@lick.pvt.k12.ca.us
>
>"Not everything that can be counted counts,
>and not everything that counts can be counted."
>--Albert Einstein
>
>
>
>---------------------------------------------------------------------------
>To unsubscribe from pinhole, send an email to requests@exploratorium.edu
>with the words 'unsubscribe pinhole' (without the quotes) in the SUBJECT
>of the email.
>
>To subscribe to the digest and only get 1 combined message a day, send an
>email to requests@exploratorium.edu with the words 'subscribe digest
>pinhole' (without the quotes) in the SUBJECT of the email.
>---------------------------------------------------------------------------

Steven Eiger, Ph.D.

Departments of Biology and the WWAMI Medical Education Program
Montana State University - Bozeman
Bozeman, MT 59717-3460

Voice: (406) 994-5672
E-mail: eiger@montana.edu
FAX: (406) 994-3190

Next message: Paul Doherty: "Pinhole List/Ganson"
Previous message: Heidi Black: "Re: pinhole journalist seeking inspirational teachers"
In reply to: bliss: "Re: pinhole friction with tires"

Date view	Thread view	Subject view	Author view

This archive was generated by hypermail 2b29 : Thu Oct 19 2000 - 11:10:30 PDT