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Gravity - Einstein vs Newton

by porkncheese
Tags: einstein, gravity, newton
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Apr21-14, 06:56 AM
Chestermiller's Avatar
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Quote Quote by porkncheese View Post
This is why I question the practicality of GR on earth.
Perhaps its because I haven't studied GR in depth but I cannot grasp the 2 previous Einstein statements.
They directly contradict Newton which is what I was taught in motion physics.
A body at rest has a velocity that remains at zero. How does something accelerate without even moving?
Suppose you're on that ride at the amusement park where the platform is rotating, and you are situated against the cylindrical vertical wall. We used to call this ride the "Roundup." At some time, the floor drops out, but you are still pinned against the wall. From the perspective of your frame of reference inside the cylinder, you are at rest. Yet you are experiencing an acceleration. This is somewhat analogous to what happens with gravity in GR (although, there, the time dimension is participating in the acceleration effect). If you are at rest in proximity with a large gravitating mass like the earth, then you are not in an inertial frame of reference.

Apr21-14, 09:57 AM
P: 17,533
Quote Quote by porkncheese View Post
This is why I question the practicality of GR on earth.
If all you want to do is describe apples falling and satellites and rockets flying around the solar system, then GR is not practical. Newtonian gravity is almost as accurate and easier to compute.

If you want to describe very fast objects, very strong gravity fields, or very sensitive measurements then you cannot avoid GR.

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