Irrelevant physics

By Marcus Wilson 06/09/2010 1

Here’s a question taken from a well-used first-year undergraduate physics text:

Suppose you are standing on the center of a merry-go-round that is at rest. You are holding a spinning bicycle wheel over your head so that its rotation axis is pointing upward. The wheel is rotating counterclockwise when observed from above. Suppose you now grab the edge of the wheel with your hand, stopping it from spinning.

What happens to the merry-go-round?

For this problem, neglect any air resistance or friction between the merry-go-round and its foundation.

Little wonder why people get turned-off physics and end up thinking that it is irrelevant to the real-world. I mean, when has anyone ever stood at the centre of a merry-go-round with a bicycle wheel above their head? All the merry-go-rounds I have seen have a pillar running through the centre making standing their impossible to start with.  And you would look so stupid that I’d challenge anyone to go and do this in public.

There are numerous more practical examples of conservation of angular momentum out there in the real world.

Later today, I get filmed as part ofthe Kudos Awards, on the ‘science communication’ work that I do. Part of what I’ll be saying is that us scientists should be making our respective subjects accessible (unlike the physics problem above). There are many people who regard scientists as boffins in white coats (I hate that word ‘boffin’ – it implies someone utterly disconnected from society) and science of being of no relevance to everyday life. I can just imagine a ‘boffin’ standing on a merry-go-round with a bicycle wheel…We scientists have a duty to show everyone just how much they rely on science for normal day-to-day activities, and that scientists themselves are not boffins but major contributers to everyone’s quality of life.

One Response to “Irrelevant physics”

• ross says:

Ah ha! If you were a rocket scientist it would have been a very valuable experiment to carry out! Something similar is used in satellites to keep them pointing the right directiom. Momentum wheels. These are (at least three(?)) spinning wheels which change their rotational speed to rotate the satellite in the opposite direction. They are a cunning way of saving fuel. So if the satellite has a tendency to always rotate in one direction, the wheel can be spun up to the maximum spped in the opposite direction and then “use up” all its rotational speed down to zero and then up to the mas rotational speed in the opposite direction. Once it has used all its rotational speed up, the operators then do a “momentum dump” (using fuel this time) to get back to square one and start all over again.

See, not so useless after all!!