Re: pinhole coefficient of friction, mass, and driving up a hill

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Tue Dec 18 2001 - 10:59:41 PST 

Message-ID: <3C1F9214.C4DCBC06@exploratorium.edu>
Date: Tue, 18 Dec 2001 10:59:41 -0800
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole coefficient of friction, mass, and driving up a hill

The dfference between theory and practice in practice
is greater than the difference between theory and practice in theory.

The approximation that the friction force is equal to a friction coefficient
times the normal force (often the weight) is one of the physics approximations
that is the worst when applied to real world situations such as cars.

Paul D

Debbie Berlin wrote:

> I was asked why people are told by mechanics that, on
> snowy days, they should put a lot of mass in the back
> of their truck if they want to go up a slippery hill.
> All simplified, high school physics problems show that
> mass cancels out when finding acceleration due to
> friction. How is this reconciled with real life? Is
> it mass distribution that matters? Total mass? And
> why?
> Thank you for your help. This will help settle a
> passionate lunch dispute!
> --Debbie
>
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