SSM has a fun physics questions over at RCG: why doesn't a tennis ball fall off his KK quad when he's flying?
Well, I wanted to return a stray tennis ball to some kids playing in the tennis courts at the local park.
So I pick up the ball and place it on top of my Quad. The ball is on an upside down plastic sandwich box (to protect the works), with a very slight indent in it, a couple of millimetres deep, so the ball rolls around and can fall off at the slightest bump.
I take off with the ball on board and fly over the court, expecting the ball to roll off at any second, and fall down to the kids. It doesn't. I rock the copter back and forth a bit. No change on the ball. I increase the strength of the rocking. The ball sticks there, like it's glued. I fly the copter around, turning, stopping and starting. No effect. I zoom the Quad up and down. To and fro. Frantically stopping, dipping suddenly, whamming it into turns. The ball doesn't budge. "What gives?", I think.
I bring the copter back to earth and place a second ball on top, with the first one. The two balls cannot both sit in the indent, and so they're now really unstable. If I carry the copter in my hand, it's hard to keep the balls on top - they fall off really easily.
So I fly the Quad with the two tennis balls on top to a position back over the court. And I do the rockin' and rollin' and shakin' thing all over again - the works. The balls just laugh at this and refuse to drop down to the kids.
In the end, the only way I can get the balls off the top of the copter, inside the tennis court, is to land the Quad. The balls fall off the instant the copter touches down, The boys are amazed.
So what gives? It's something to do with the fact that every time the copter dips in a certain direction, it accelerates in that direction? And this acceleration perfectly balances the inclination, so the ball/s stay centered and don't fall? Even with all that starting, stopping, turning and zooming?