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The Einsteinian '''principle of equivalence''' of acceleration and gravitation says that those two things are indistinguishable by any experiment and so all the features of one must show up in the other.  

The Einsteinian '''principle of equivalence''' of acceleration and gravitation says that those two things are indistinguishable by any experiment and so all the features of one must show up in the other.  

It can be used to derive some properties of gravitation with the example of accelerating vehicle as e.g. a rocket ship or an elevator, in which case it is called "Einstein's elevator".

It can be used to derive some properties of gravitation with the example of accelerating vehicle as e.g. a rocket ship or an elevator, in which case they are called "Einstein's rocket ship" or "Einstein's elevator".