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# Why NASCAR drivers are like astronauts

By PETE GRATHOFF
The Kansas City Star

Kevin Harvick didnt mince words when asked by The Star about critics who say NASCAR drivers are not athletes.

Anybody who doesnt think there are athletes riding around in those cars is absolutely crazy in my mind because ... when youre racing, you feel the Gs on your neck, your arms, your shoulders, Harvick said in 2001.

By Gs, Harvick means G-force. While we often think of astronauts when talking about G-forces, NASCAR drivers experience this in every race. G-force is the force a mass experiences due to acceleration.

In her book The Physics of NASCAR, author Diandra Leslie-Pelecky wrote that NASCAR drivers routinely experience 2g to 3g in the turns. While 1g is the force we normally feel, Space Shuttle astronauts feel a 3g force on launches.

Think about that as you watch the races this weekend at Kansas Speedway.

The reason drivers feel that force can be explained by Isaac Newtons first law. Known as the Law of Inertia, it states that Every object persists in its state of rest or of moving uniformly straight forward unless it is compelled to change that state by forces impressed on it.

Since NASCAR races are not held exclusively on straightaways, there must be a force that pushes cars as they make turns on the track.

This inward-pointing force is called the centripetal (which means center-seeking) force, Leslie-Pelecky wrote. The centripetal force is the reason cars turn.

But if youve been in a car that makes a sharp left turn  as they do in NASCAR  you know that your body moves to the right while the car is moving to the left. That would seem to indicate the force is pushing to the right, but thats not the case.

The force is actually pushing to the left. How can that be?

Just as you feel pushed backward when you accelerate (even though the force is pushing you forward), Leslie-Pelecky wrote, you feel pushed toward the outside of the circle even though the force making you turn is directed toward the center of the circle.

As the car turns, the driver also turns, because he is strapped to the vehicle. But his body wants to move forward (as Newton told us), so the driver feels the centripetal force.

As Leslie-Pelecky wrote at her Web site stockcarscience.com: The seat (via the car) is exerting a force on him toward the inside of the turn while hes trying to go straight. The net result is that the driver perceives a force to be acting outward, but it is actually acting inward.