Playing with Toys in Space

Looking for a clip to illustrate momentum? Footagevault has provided this footage of astronaut Jeff Hoffman playing with a red toy car on a looped race track on board the Space Shuttle. The car's momentum and centripetal force keep it on the race track initially, before friction slows it down.

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matt perks

Circular momentum? On a perfectly circular, frictionless, weightless track the car would stay on the track, at any speed, because the contact force from the track on the wheels would be exactly the required centripetal force to keep the car in circular motion.

The car comes off because the situation is not perfect. For some reason the size or direction of the resultant force is not quite the same as the required centripetal force. Possible reasons that occur to me are; the astronaut not being able to hold the track 'still', the track not being perfectly circular, or being 'bumpy' in some way, uneven bearings in the car's wheels. Any of these could cause an increase in the size of the resultant force so that the car leaves the track.

Worth noting that once the car leaves the track its CoM moves at a steady speed in a straight line but the tumbling makes this hard to see.

Anna Richardson

Hello Matt,

The description has now been changed to reflect your comments.

Kind regards,