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5 Fundamentals of general relativity

# 5.1 From special to general relativity

In general relativity, the “force of gravity”, which directly couples to a gravitating body through its mass, is replaced by relationships between geometric coordinates. This can be done because the inertial mass that relates the acceleration of a body from rest (a purely geometrical aspect) to the force through Newton’s second law F = m a, is the same as the gravitational mass that couples the gravitational acceleration g to that body Fgravitation = m g. Newton tested this equivalence using various pendulums, and Eotvos [75] in 1889 verified the equivalence of inertial and gravitational mass to better than one part in 109. Gravity attracts different masses in a way ...

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