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December 12, 2008

Strange But True!

Q. If given an opportunity to “drive through the sound barrier” in a jet-powered car, would you go for it?

A. The current land-speed record was set in 1997 in the Black Rock Desert of Nevada by the jet-powered car Thrust SSC, says Jearl Walker in “The Flying Circus of Physics.” Its speed was 759 mph in one direction and 766 mph in the opposite direction, both exceeding the speed of sound of 750 mph and sending shock waves (sonic booms) across the desert floor. The dangers here were many, such as the chance of air pressure under the car's nose lifting it and flipping the car over backwards (while traveling faster than sound!). A more subtle danger was to the wheels, rotating in excess of 6,800 revolutions per minute and with a huge centripetal acceleration of 35,000 Gs (35,000 times gravitational acceleration) on the rims. This took the cast aluminum wheels to the edge of what they could withstand without rupturing. Had one hit even a small object, the shock would have caused the wheel to explode and the car to crash. “Because that part of the desert had once been used for artillery practice, the ground crew had to walk the route to carefully inspect for partially buried artillery shells and similar debris before the car could be run along its course.”


 
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