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OBJECTIVE
THE
PHYSICS Whenever
a moving body changes its direction, it accelerates and therefore must
experience a net force. In the case of a car traveling in a circle, the force
must be directed towards the center of the circle in order to pull the car
around the circle. Turns on a racetrack are approximately arcs of circles. The
"center-seeking" or centripetal force must get larger as the speed
of the turning car increases and as the radius of the turn gets smaller. In
order to win at Indianapolis, cars must make a series of very tight turns with
small radii of curvature at very high speeds. Thus they need large amounts of
centripetal force.
SOMETHING
EXTRA The
black streak on the track marks the groove, the preferred path of racecars
around the track. Notice that cars approach turns so that they ride very high
on the turn and narrowly miss the wall. This means that they must make a very
sharp turn, but it also allows the driver to use part of the weight of the car
to slow the car as it climbs into the turn and to increase its speed as it
comes out of the turn and down the slope of the track to the straightaway. If
no net force acts on a body, it will continue traveling in a straight line at
a constant speed (Newton's First Law). Thus if a car doesn't have enough
centripetal force to pull it around a turn, it will travel tangent to the
curve it meant to follow and thus hit the wall. Common accidents at
Indianapolis occur when a driver takes a curve a little too fast and brushes
the wall because the lateral adhesion of his car and the part of its weight
directed towards the center of the turn do not provide enough centripetal
force to pull him around the turn at a small enough radius.
OTHER
EXAMPLES If you do not wear a seat belt and the car you are riding in makes a sharp turn, you are apt to slide along the seat of the car towards the out- side of the turn. This happens because there is no centripetal force pulling you around the turn. When you wear seat belts, they provide; the centripetal force.
Bicycle
riders lean towards the inside of a curve so that their weight will provide part
of the centripetal force pulling them around the turn. Some
roller coasters travel around a complete loop so that at one point the car and
the passengers are upside down. Passengers don't fallout of the car because the
car is moving fast enough so that the passengers' weight at the top of the loop
goes into providing centripetal force for the turn. No force is left over to
accelerate the passenger out of the car.
When
you lift a spinning beater out of the batter, the batter splatters around the
kitchen. This happens because the adhesive force between the batter and the
beater does not provide the centripetal force necessary to pull the batter
around a circle with the beater, so the batter flies off in a straight line at
constant speed. |
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In
order to travel around a curve, a car must experience a force towards the
center of the turn. This inward force is called 
If
the track were flat, the force pulling the car around the curve would be
provided by the adhesion of the car's tires to the track, which is the
frictional force between the tires and the track. Thus racing speeds would be
limited by the friction available between the tires and the track. In order to
allow higher speeds, the track at Indianapolis is banked so that it slopes
towards the center of the turns. When a car goes around the turn, part of its
weight pulls it towards the center of the turn and provides some of the
centripetal force needed to swing it around the turn. 
