Tuesday, 13 May 2014
My fourth of four classes launched their rockets today and I’ve just gotten the routine down. At launch time, the kids have to measure a few data points so they can later calculate the rocket’s maximum height.
Back when I showed the kids how to use the Impulse-Momentum Theorem to do the calculations (it was a little trickier because the rocket’s thrust isn’t constant nor is its mass), we admitted the physics could be off. Way off. Is that the case? Today, one class did their calculations and they came out about like this: we measured the rocket’s max altitude of approximately 65º from a distance of about 60 meters from the launch pad. That yields an altitude of about 125m.
Were we off? The calculations predicted something between 200 and 300 m. So a measurement of 125 m is way low. I remain unconvinced the kids got good measurements yesterday, though. Estes reports the our configuration, a Viking Rocket with an unspecified motor can get up to 1600 m and a YouTube reviewer says about 200 m. That latter number is between what we calculated and measured, but closer to our calculations. Note to my next year self: figure out a better way to measure the rocket’s maximum altitude. Could be more people spotting the same rocket to measure angle. Could be more careful supervision of the kids measuring. I’m not sure.