Wednesday, November 19, 2008

Physics: Stopping on a dime

This week the kids used their physics skills to solve an engineering problem: What is a safe distance between an out-of-bounds line on a basket ball court and a wall or other obstruction? To figure this out the kids carried out several experiments. First they measured their reactions times: Kids worked in pairs and took turns trying to catch a falling meter stick. The point on the stick where the person caught it was used to calculate the subject's reaction time.* Then everyone in the group was timed running a 25 meter course in addition to measuring the distance each runner overshot the finish line.

After an involved discussion about the challenges of safe design in general, the kids decided that it makes the most sense to consider the slowest reaction time, the fastest speed, and the longest overshoot in order to come up with the safest estimate for the distance between the out-of-bounds line and other obstructions. Next week we will do the final calculations, i.e. multiplying the fastest speed by the slowest reaction time to get the distance a runner might travel while reacting and added it to the overshoot distance (the distance one travels while physically trying to stop - people don't usually stop on a dime, particularly not during a competitive sport like basketball.)

* I just gave the kids a chart of distance fallen vs time, but as you physics geeks out there know, you get this by solving for t = the square root of (2d/9.8). Basically if you know how far an object has fallen, and you know the acceleration of gravity ( 9.8 meters/seconds squared), you can figure out the travel time, which for our purposes indicated the reaction time. The reason we didn't just time it, is that reactions time are really short, difficult to measure, and these measurements would themselves be unfairly

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