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Albert Einstein in his equivalence principle stated that a freely falling body does not experience force, but if I let a ball free fall its velocity increases periodically (it accelerates). How is this possible without a force being involved?

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The reason the object appears to fall is from curved space time. It's not that the object is accelerating towards the Earth but instead space time it self curves towards the Earth. This means that strait lines through space time look curved from the reference frame of objects in micro gravity. The ground actually accelerates up at $9.81\ \mathrm{m/s^2}$ through space time but the Earth does not expand because space time curves in such a way that it cancels out the effect of the acceleration of the ground on the size of the Earth.

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  • $\begingroup$ what is micro gravity? $\endgroup$ – Shashwat Dec 5 '15 at 19:57
  • $\begingroup$ @Shashwat Microgravity is when there is gravity but its effects are negligible. $\endgroup$ – Anders Gustafson Dec 5 '15 at 21:10

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