|MadSci Network: Physics|
Dear Ray, Thank you for responding to my post and letting me try to be clearer. You are absolutely right. In general, a frame on the Earth is not going to be in free fall, and will therefore not be an inertial frame. I just meant that since the Earth, and any frames on the Earth, are in orbit around the Sun, the SUNís gravitational force, and subsequent acceleration of the Earth because of it, is not what causes a frame on the Earth to be non-inertial. As you say, it is the Earthís gravitational force that causes an Earth-bound frame to be non-inertial. A frame, like the International Space Station, that is in free fall about the Sun AND the Earth, IS inertial. In your initial question, you asked that since the Earth was in orbit around the Sun, and therefore accelerating, shouldnít that preclude the application of Special Relativity. I was trying to draw a distinction between the gravitational force due to the Sun and that due to the Earth. The effects of the force from the Sun are largely removed by the motion of the Earth and therefore the Sunís force is not what causes an Earth-bound frame to be non-inertial. The gravitational force due to the Earth is what causes an Earth-bound frame to be non-inertial. For a frame to be inertial, the effects of that force also have to be removed by an additional acceleration, like that of the motion of the ISS. I hope that clears up any confusion that I caused with my first post. Please let us know if you would like some more information. Sincerely, Jim Guinn Georgia Perimeter College
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