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Physics/Angular Momentum


Hi Steve,

I came across a physics cartoon online which states something like the following:

What are you doing?
Spinning counterclockwise
each turn robs the planet of angular momentum
slowing its spin the tiniest bit
lengthening the night
pushing back dawn.

I just was curious about the physics validity of this statement. It seems to me that this is an involved question, and I'm not really sure how the actual mechanics would work. Would the direction in which the person spins depend on where on the earth he/she were located? If it were at the equator, is there a perpendicular factor involved? Which direction would actually make sense to increase or slow the rate of spin. And is this actually real physics?

Essentially, I'm just looking for someone to shed light on this cartoon. Please let me know your thoughts.


That depends on which hemisphere it's in, and it would be an incredibly tiny effect.  You'd have to be in the northern hemisphere.  At the equator, you'd just be introducing precession (tilt of the axis).  It's real physics, of course, but it's ridiculous.  The Earth has a mass of nearly 6*10^24 kg, trillions of trillions of our mass is insanely small in comparison and our radius is (compared to 6.38 million meters) also ridiculously small.  So our moment of inertia is absolutely unmeasureably small in comparison.  Worrying about it being real physics is, in the end, completely unimportant.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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