By: Beth Bemis

How many times have you watched a football game and cringed as two players collided? No pain, no gain, right? That's why they're paid the big bucks. But what really happens when two football players smash into each other, from the viewpoint of physics? How much force and energy are involved?

You can get a lesson on the physics of collision in The Sporting Life by Susan Davis and Sally Stephens. This neat book on the science of sports is part of the Exploratorium's Accidental Scientist series, published by Owl Press. Here's how Davis and Stephens explain how to figure the physics of a football fracas.

Suppose running back Terry Kirby of the San Francisco 49ers and strong safety Leroy Butler of the Green Bay Packers go head-to-head. If you can calculate how much kinetic energy they had before the collision, you can find out how much total energy is involved; once they've crashed, the kinetic energy goes almost to zero since they1re no longer moving.

Energy is equal to 1/2mv2, where m=mass and v=velocity; so you need to know each player's mass and speed. Let's suppose that Kirby weighs approximately 220 pounds and Butler weighs about 231. Converting that to kilograms (there are 2.2 pounds in a kilogram), puts Kirby at 100 kilograms and Butler at 105 kg.

Imagine Kirby and Butler sprinting toward each other going 6.75 meters per second; that's just over seven yards per second. One half times 100 kg times 6.75 m/sec squared is about 2278 joules (the units used for energy). One half times 105 kg times 6.75 m/sec squared is about 2392 joules. That makes Kirby and Butler's collision energy more than 4670 joules -- enough energy to move 23 tons one inch! That's like lifting a compact car about 2 feet into the air.

So, where does all this energy go? When two objects collide, they both deform. In other words, bodies get smashed. Some energy is released as heat, but often that energy leads to bruises, bleeding and broken bones as the colliding bodies absorb the energy. Hopefully, the players don't focus too much on the physics of collisions before they run out onto the field. But now, you can calculate the actual force and energy while watching the game (don't forget your calculator!).

If you're looking for more math and physics sports activities, check out The Sporting Life. As the authors promise, you'll discover the unexpected science behind your favorite sports and games.

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Do levees and dams prevent flooding, or could they increase the potential for large-scale flooding? Explore and discuss ideas and philosophies of flood control and water quality with Dr. Jeffrey Mount of the UC Davis Geology Department. He'll be the lecturer at the next Cutting Edge of Science lecture, to be held on Tuesday, January 20 at 7:30 p.m. at the Davis Senior Center. The lecture titled "Lessons Learned, Yet Again: Floods of 1997" is free to the public.

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Explorit would like to say a final thanks to the management of the County Fair Mall in Woodland for donating a store front to Explorit during the holiday season. The Exploration Station was a huge success, reaching thousands of people. Explorit would also like to express appreciation to the communities of Woodland and Davis for their support and extend a welcome to all of the new discoverers of Explorit1s unique approach to hands-on science.

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Explorit Science Center is located at 3141 5th Street in East Davis. The current exhibition is Wonderful Waves: The Science of Sound and Light. Public hours are Saturday from 11 a.m. to 4:30 p.m., Sunday from 1:00 to 4:30 p.m., and Tuesday through Friday from 2:00 to 4:30 p.m. Regular admission is $3; members, teachers, and children under 4 are free.