Gravity - Part 11
I can summarize the Gravity Principle again as:
Gravity makes the apple have a type of "inertia" where it will not change its acceleration 32 unless acted on by an external force, like your hand, or when it reaches the ground. It wants to keep the motion of "acceleration of 32 downwards." That is the motion which gravity is forcing it to keep. The gravitational INTERACTION between the apple and gravity compels it to stay that way.
Now we consider George, another observer. He is in motion relative to you, who is standing firmly on the ground. What is George's motion? He is free-falling with the apple, so that the apple stays right beside him. To him, as you can see, the apple is not moving at all.
Proving the Relativistic Energy-Momentum relation, the hard way and the easier way.
This adds the proof for the relativistic mass effects from motion, proving that gravity causes it.