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Physics/Circular motion


If we consider that mass in motion will change both direction and velocity if being hit by another mass(force) that moves normally regarding its movement why doesn't the Moon in that case change velocity together with direction while moving around the Earth considering the gravitational force(gravitons) acts normally to the Moon's direction?What am I missing?

A couple of things. I'll start with the basics, assuming circular orbit. First, forces. If the Earth's gravity got stronger, the Moon would be pulled in at an angle and speed up. Weaker, it would go outward (slowing down, doing work against gravity). Both scenarios would change velocity. The force is in balance to keep the velocity even. Second, the graviton has no mass and is being exchanged evenly between the Earth and Moon, so no exchange of graviton momentum. Third (and last), the Moon is in an elliptical orbit, so it actually does speed up and slow down in parts of its orbit.  


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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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