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Skids and Cars
Name: Shannon T.
Status: N/A
Age: 16
Location: N/A
Country: N/A
Date: 2001-2002
Question:
I am studying physics and was wondering what a skid is,
how it happens and how you can recover - from a physics perspective. I am
also required to research 'hand-brake turns' and have come up with no
information. Can you please help?
Replies:
Shannon,
A skid occurs when the road and wheel cannot exert enough friction to hold
onto each other. A skid is very much like your foot sliding on ice. It is
the same as a box sliding across the floor. If a car slams on the brakes so
that the wheels stop rolling, the car may stop immediately. If the road
cannot apply enough friction to make the car stop, the car's will skid to a
stop over more time (it will not be immediate). In a sharp turn, sideways
force is needed to make the car change direction. If enough friction from
the road cannot be provided, the car will "spin out" rather than making a
turn.
Dr. Ken Mellendorf
Illinois Central college
I believe that this has to do with the difference
between static and dynamic friction. When a wheel is
rolling, it clings to the road via static friction (at
any moment, there is a patch of tire that is touching
the road, but is not sliding against it). When the
brakes are applied too hard, the wheels lock up. This
would cause the patch of tire touching the road to
slide. Since it is now sliding across the ground, the
friction involved is now dynamic friction. For most
materials, dynamic friction is only half that of
static friction. This means that the car will not
stop as quickly. More importantly, when the tires
lock up, the car will slide (skid) in the direction it
was going. Since your wheels are no longer rotating,
you have no control of where the car is going.
Anti-Locking brakes solve this problem by allowing you
to brake in pulses. During a pulse, the tires lock
up, and you will slow down. When the pulse ends, you
get a little bit of control as the wheels are
momentarily allowed to rotate.
I believe that a hand-brake turn is when you use the
parking brake to help in turning. Make a sharp turn
in the snow. When your car begins to turn, apply the
parking brake. This will lock up your rear tires,
causing the car's back end to swing forward. When it
is facing the direction you want to go, release the
parking brake.
I have never tried this move before though, and do not
recommend anyone trying it either. I have heard that it
works best with rear wheel drive cars with manual
transmissions.
If anyone have a better answer, please let me know.
-Wil
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