Re: Friction
John's answer reminded me of our exhibit at The
Science Place called Our Friend, Friction.
In this exhibit, you apply the same impact
force to six wooden blocks to cause them to slide up a stainless steel ramp
divided into lanes. The blocks all have the same mass but each has a different
bottom surface with a different coefficient of sliding friction against the
steel surface. Accordingly, even though all blocks weigh the same and all
receive the same impact from spring guns, each block slides to a different
height up the ramp. The inclination angle of the ramp ensures that the blocks
return to the spring gun position.
The exhibit sign says, "The force of friction
is probably the most common force in our everyday lives, but we usually think of
it only as a nuisance force that causes moving objects to slow down and stop.
Without friction we could not: walk, ride a bicycle or drive a car, brake a
moving vehicle, pick up or hold an object by gripping it between thumb and
fingers, warm our hands by rubbing them together, stab and pick up a piece of
food with a fork, write on paper with a pencil, or even hold the pencil in
writing position. What everyday activities can you think of that depend on
friction?"
Paul O. Johnson
Exhibit Developer
The Science Place
Dallas, Texas
.
----- Original Message -----
Sent: Saturday, February 02, 2002 9:03
AM
Subject: car acc
> IMHO best answer is none of the above (if we're
> striving for
clarity with our students). A force
> diagram would show a drag force
(mainly rolling
> friction) opposing motion and the force of the
road
> pushing forward on the car. This latter force is an N3
>
reaction to the rearward push of the tires on the road
> which is only
possible if the surface is not
> frictionless. This is the same process
that allows us
> to walk. John Barrere
>
>
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