Re: [Phys-l] [tap-l] stopping distance

[Rick Tarara <rtarara@saintmarys.edu>]

The 'mg' is the normal force (level road) in the frictional force  mu x 
Normal.

As to the problem itself, if we try to stay close to the simple 
intro-frictional model then I'm going to say that the problem is primarily 
one of temperature change--both at the brake pad/disk--drum interface and 
the road/tire interface which will end up changing the frictional 
coefficients (in most cases lowering them with increasing temperature).  The 
more massive vehicles will develop higher temperatures as their increased KE 
is converted to thermal energy.

Rick

***************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN
rtarara@saintmarys.edu
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Free Physics Software
PC & Mac
www.saintmarys.edu/~rtarara/software.html
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----- Original Message ----- 
From: "Richard Heckathorn" <geepaw@wowway.com>
To: <tap-l@lists.ncsu.edu>; <phys-l@carnot.physics.buffalo.edu>
Sent: Friday, January 05, 2007 12:07 PM
Subject: Re: [Phys-l] [tap-l] stopping distance


> Greetings,
>
> Is there something wrong here?
>
> W = KE
> fd = 0.5mv2
> mmgd = 0.5mv2
> mgd = 0.5v2
>
> The acceleration you describe 'mg' is the
> acceleration due to the pull of the earth on the
> object. This is at right angles to the movement of
> the object. How could this force slow down the
> object?
>
> Dick
>
> Helping teachers who facilitate, motivating
> students who learn.
> Dick Heckathorn  14665 Pawnee Trail  Middleburg
> Hts, OH  44130  440-826-0834
> www.cvcaroyals.org/~rheckathorn/
> Adjunct Physics Teacher - Baldwin Wallace College
> Physics is learning how to communicate with ones
> environment so that it will talk back.
>
>
> -----Original Message-----
> From: tap-l-owner@lists.ncsu.edu
> [mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of
> Anthony Lapinski
> Sent: Friday, January 05, 2007 8:50 AM
> To: tap-l@lists.ncsu.edu; tap-l@lists.ncsu.edu;
> phys-l@carnot.physics.buffalo.edu
> Subject: [tap-l] stopping distance
>
> Using the Work-Energy Theorem, you can determine
> how the stopping distance
> is related to the car's initial velocity:
>
> W = KE
> fd = 0.5mv2
> mmgd = 0.5mv2
> mgd = 0.5v2
>
> If we assume the brakes "lock" the wheels to
> create a skid mark, then the
> above result shows that the stopping distance does
> NOT depend on the car's
> mass.
>
> However, students tell me and Driver Manuals often
> state that the weight
> of the vehicle IS a factor (heavier = longer
> stopping distance). In the
> above calculation, I am dealing with an idealized
> case, but in "real-life"
> anti-lock brakes change the actual stopping
> distance depending on the
> weight of the vehicle. I've also heard that large
> trucks have a unique
> braking system. Can anyone elaborate on these
> ideas?
>
>
>
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