You'll get a better sense of these tricks by watching the video, but here are a few brief descriptions:
Shoot the Planets: The yo-yo orbits the earth, the moon and does a tethered assist (better known down on earth as man on flying trapeze) three times before unwinding and returning to the palm.
The Asteroid: The string is uncontrolled and limp, basically bouncing back and forth. The trick here is to not get hit on the head.
There's a lot of physics involved with yo-yos, Pettit explains. There's angular momentum involved with the yo-yo spinning and moving in an arc, and linear momentum with the yo-yo going in and out of the string. There's also slight energy expenditure with moving parts and drag with air (less of an issue in space).
"I haven't been spending as much time as I should working on my yo-yo training," Pettit said citing his rustiness. "It just shows I've got misplaced priorities."
It's OK - we're sure you have more important things to do on the ISS.
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