A Pound of Feathers

Had an interesting discussion with WiseKid about gravity this evening. Seems they are doing something called physics in school, although he detests the teacher who just makes them learn formulas.

Anyway, we were discussing how fast a one kilo bar of lead would be moving when it hits the ground after being dropped from 150 meters height. I then asked him how fast a kilo bag of feathers would be going if dropped from the same height, and which one would get there first if dropped at the same time.

A bizarre discussion ensued, as he was completely and utterly sure that the bag of feathers would reach the ground first. His reasoning was: there would be less drag on the bag of feathers so it would reach the ground first. We tried to get him to imagine just how big a kilo bag of feathers would be. No avail. We tried a vacuum - yes, he remembered us dragging him as a kid to some science museum where he had experimented with a vacuum. And yes, he was clear on the fact that in the vacuum the feathers and the lead would reach the ground together. But we could not convince him that because of the resistance (all that surface area on the feathers!) the lead would hit the ground just before the feathers.

And we've even been to Pisa with him and discussed the experiment there. But what do we know, old fuddy-duddies that we are? 16-year-olds know everything, his face said as he gave up in exasperation and went for a smoke.

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