Skipping merrily along I have now another comment on Bill S.'s book about gravity
Originally Posted By: Bill S.
We should look more closely at the concept of the “equal and opposite force”. When I pick up a stone from the surface of the Earth, then let go of it, it falls back to the surface. Is it the “equal and opposite force” that causes it to fall? It might be tempting to think so, especially in view of the idea that it is the energy I put into the stone by lifting it that caused it to fall back to Earth, but, in fact the answer has to be “no”. When I pick up the stone, my weight increases; in other words my feet press more firmly against the ground. This must be the “equal and opposite force”, but wait, it does not end here. As my feet exert more force against the Earth, the Earth pushes back more firmly than it did before, so where does it end? It seems that it is not the “equal and opposite force” that is involved in gravitational attraction.

Actually the "equal and opposite force" involved in a rock lifted above the surface of the Earth is the force that causes the Earth to move toward the rock. Let's skip the lifting part and look at the rock as it moves toward the ground, to simplify what we are talking about. The rock falls towards the Earth because gravity causes a force to act on the rock. But at the same time that the rock is falling toward the Earth, the Earth is falling toward the rock. The "equal and opposite force" is the force pulling the rock toward the Earth. The mass of the Earth is a lot larger than the mass of the rock, so the rock moves the farthest and fastest, but both of them are moving.

Bill Gill

C is not the speed of light in a vacuum.
C is the universal speed limit.