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CENTRIPETAL
FORCE
UNIT 6,7,14 Dr John P.=
Cise,
Professor of Physics, Austin Community College, 1212 Rio Grande St. Austin =
Tx.
78701 jpcise@=
austincc.edu & New =
York
Times May 10, 2008 by John Branch
The Track That Defied the Writing on the Wall
=
Spen=
cer
Jones/Associated Press
Ralph Earnhardt spinni=
ng out
during the 1962 Rebel 300 at Darlington Raceway. The track had two races a =
year
until 2004.
By JOHN BRANCH
DARLINGTON, S.C. — Harold King maneuvered the=
car
onto the track at Darlington Raceway, Nascar’s original superspeedway. He
punched the gas and steered the car high around the banked corner. Skip to next paragraphTh=
en he
stopped and put it in reverse. King
is 83. The car was a Dodge Grand Caravan, with the air-conditioning on, goi=
ng
about 30 miles an hour. It felt more likely to tip over on the 25-degree
corners than to become the latest car to scrape the wall=
and
sport the famous Darlington Stripe down its right side. The van glided along
the wall, white-washed and ready for Saturday night’s Dodge Challenger
500. “See how the wall comes in?” King said, pointing toward the
illusion — or is it real? — of the wall’s bending inward =
as
it curves toward the straightaway. He hit the brakes, backed up, and drove
through the corner again, more slowly.&nbs=
p;
“I wish you could see it when they haven’t painted
it,” he said. King, born and raised in Darlington County, is a living
bridge to Nascar’s roots, one of the few still alive who were at
Darlington’s first race in 1950, when this little egg-shaped oval ush=
ered
in the modern, paved era of stock-car racing.
Question: =
Find the
maximum speeds in turns 1&2 and
then turns 3 & 4 where the cars would receive their
Centripeta=
l force solely
from turn banking? Hint: Tangent theta =3D[sin theta/cosine theta] where th=
eta =3D
angle of banking. Make a free body diagram showing forces in the vertical a=
nd
horizontal direction. Set up =
two
equations of motion: one for the vertical and one for the horizontal direct=
ion.
There is no acceleration in the vertical direction.
Accelerati=
on does
exist in the horizontal direction. Answers: turn 1 & 2: 107 ft/s or 73.=
23
mph, turn 3 & 4: 88.5 ft/s or 60.35 mph.
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