Einstein - Gravity Near the Earth the effects of the pull...

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Einstein's Principle of Equivalence Einstein's General Theory of Relativity is based on another principle of equivalence. This asserts that to a local observer (an observer inside the system), the effects experienced because of an acceleration are indistinguishable from the effects caused by a gravitational field. If an astronaut was trapped inside a spaceship with no window, and the spaceship was accelerating upwards at 9.8 m/sec 2 , there is no experiment he could do to determine whether he was still on earth, or accelerating at a remote location in outer space. Tides In addition to the force of gravity from the earth, every object on the earth must necessarily feel a force from the moon and the sun. However, the earth is in free fall in relation to both these bodies. Just like the astronaut on the space shuttle discussed in
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Unformatted text preview: Gravity Near the Earth the effects of the pull due to the sun and earth are "cancelled out" because of the free fall. Yet this cancellation is not exact; a small net force is exerted by both the moon and the sun on all objects on the earth. For objects fixed to the surface, this force is not significant. However, it does act on the oceans, causing them to bulge toward the moon (or sun) where the moon is closest to the earth and the force is strongest, and to bulge away where the force is weaker (on the opposite side from the moon). Figure %: Effects of moon's gravity on earth's oceans. As the earth rotates on its axis, the region facing the moon changes, causing the earth to shift slightly under the oceans. This effect accounts for the daily rise and fall of the tides....
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