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Re: Friction



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At 08:53 AM 10/29/98 -0500, John DaCorte wrote:
Hi,

I was wondering if someone could help me with a demonstration I have had
trouble with. I place a block of wood on a tilted desk and tilt it to
the angle that just makes the block move and secure the desk. Then I put
the block on another edge (with a different surface area) to show that the
frictional force and the coefficient of friction do not change with
surface area. The problem is that the block always stays put on the side
with the large surface area and slides on the side with the small surface
area. Any explanations? Thanks in adavance for any help.

All the physics book tell us that the frictional force is independent of the
area. One year a student listened to yours truly repeating the idea. Student
then asks, "Well, if the area doesn't matter, then how come fat tires on a
race
car corner better than skinny tires?"

I don't recall what my reply was, possibly this would be a case of the mind
expunging a painful memory so that I could remain happy, anyway, I really
didn't have any good ideas on the subject.

I finally decided that maybe the books had it wrong.

Glenn Knapp
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Physics Kahuna
Kahuna Physics Institute - on the flapping edge of physics research.
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<html><div>At 08:53 AM 10/29/98 -0500, John DaCorte wrote:</div>
<div>&gt;Hi,</div>
<div>&gt;</div>
<div>&gt;I was wondering if someone could help me with a demonstration I
have had</div>
<div>&gt;trouble with.&nbsp; I place a block of wood on a tilted desk and
tilt it to</div>
<div>&gt;the angle that just makes the block move and secure the
desk.&nbsp; Then I put</div>
<div>&gt;the block on another edge (with a different surface area) to
show that the</div>
<div>&gt;frictional force and the coefficient of friction do not change
with</div>
<div>&gt;surface area.&nbsp; The problem is that the block always stays
put on the side</div>
<div>&gt;with the large surface area and slides on the side with the
small surface</div>
<div>&gt;area.&nbsp; Any explanations?&nbsp; Thanks in adavance for any
help.</div>
<br>
<div>All the physics book tell us that the frictional force is
independent of the area.&nbsp; One year a student listened to yours truly
repeating the idea.&nbsp; Student then asks, &quot;Well, if the area
doesn't matter, then how come fat tires on a race car corner better than
skinny tires?&quot;</div>
<br>
<div>I don't recall what my reply was, possibly this would be a case of
the mind expunging a painful memory so that I could remain happy, anyway,
I really didn't have any good ideas on the subject.</div>
<br>
<div>I finally decided that maybe the books had it wrong.</div>
<br>
Glenn Knapp
<br>

<font face="Times New Roman, Times" size=4>-----------------------------------------------------------------<br>
</font><font size=3>Physics Kahuna<br>
Kahuna Physics Institute - on the flapping edge of physics research.
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