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Physics/Circular motion

Question
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?
Thanks...

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

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