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August 03 Spinny Weight Loss: the answers!My friend Mike Seyfang (Fang) was recently listening to a Science Hour podcast. The subject was "Spinny Weight Loss" by Isaac Dolom, and it was all about centrifugal force. This is the description of how things flee from the centre when they are spinning around:
Fang asked some questions about this - and good old Michael Kennett had the answers! Michael's approach was to "reformulate Fc (above) in terms of angular velocity - it is much easier to work with".
Here are the questions Fang posed:
Q: how many KG would a 100KG person ‘lose’ by moving from pole to equator? A: The answer is 345 grams (0.345 kg) - about the weight of a small bottle of water.
Q: how many KG does the Space Shuttle ‘lose’ by launching in southern Florida vs the far north of USA? A: The space shuttle at lift-off weighs 2,053,631 kg (yes, 2 million kilos) so the benefit is 7085 kg, by launching from the equator.
Q: how short would a day have to be for a 100KG person at the equator to be ‘in orbit’ or weightless? A: Actually the 100KG is a red herring in this case. We want to know how fast the earth must spin to increase centrifugal force at the equator to match gravity (9.8 m/s2). For an object to become "weightless" at the equator, the earth would have to spin 17.01 times faster on its axis. At this speed, a day would be 1 hour and 25 minutes long (a bit like the story of The Little Prince?). Blood would not stay within the confines of our bodies and people living at the equator would drift off into space. This speed would have geo-physical effects on the structure of the planet (global warming is a another way to have structural effects on the planet).
Strangely enough, if you lived on this super-fast moving earth and started walking from the pole, your weight would be normal (eg 100KG) as you left (centrifugal force is zero at the poles), and you'd get increasingly light-footed as you progressed towards the equator. By the time you arrived, you'd be floating rather than walking! This is also true of the Shuttle - it would be floating above its launch pad in southern Florida.
So now you know.
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