Physics and Evel Knievel

Posted by Paul A. Heckert Dec 14, 2007

Evel Knievel died last week. He first became famous in the 1960s as a daredevil jumping his motorcycle over cars, busses, and so forth. He wasn't always successful, breaking about 40 bones in his career.

Figuring out how fast Evel Knievel needed to launch his motorcycle to make a jump involves physics projectile motion problems. A projectile launches at some initial speed and angle. Once released, only gravitational forces act on it until it hits the ground.

How fast did Evel Knievel need to ride his motorcycle to complete his jumps? We need to know the distance of the jump, the height of the landing compared to takeoff, and the angle of the ramp propelling him upward. A 45 degree angle would give the greatest range but is unrealistic. A ramp at a 10% grade would be more realistic. Let's assume he lands at the same level he takes off from. Let's also neglect air friction, which means he would need to start a little faster to make a jump.

Doing the calculation, I get a minimum speed of a little over 100 miles per hour for one of his famous early jumps - 150 feet over 19 cars. That's not impossible, but missing the landing would result in broken bones or worse.

Evel Knievel's most famous attempt was the Snake River Canyon in 1974. Doing the same calculation, I find that jumping nearly 1600 feet requires a minimum projectile launch speed of over 330 miles per hour from a 10% slope. He attempted that jump on a rocket propelled motorcycle, so it was not a projectile in the physics sense. The rocket continued pushing him forward, eliminating the need for this impossibly high initial speed.