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Strong Equivalence Principle of Gravitation

by Ron Kurtus (updated 30 May 2023)

The Strong Equivalence Principle of Gravitation (also known as the Einstein Equivalence Principle) states that the effects of acceleration are indistinguishable from those of gravitation.

In other words, the principle extends the equivalence of masses to state that observations of acceleration cannot be distinguished from gravity.

(See Artificial Gravity for an example of this.)

Questions you may have include:

This lesson will answer those questions. Useful tool: Units Conversion

Experiments by observer

This means that an observer cannot determine by experiment whether he or she is accelerating or in a gravitational field. In other words, results from experiments in an accelerating spaceship would be the same as those obtained from gravitation.


Experiment in accelerating spaceship

Note: One problem with this concept is that acceleration cannot be applied for too long a period, because the spaceship would soon reach the speed of light. On the other hand, gravitation is continuously present.

Einstein's conclusion

Einstein concluded that gravitation and motion through spacetime are related and that the Strong Equivalence Principle suggests that gravitation is geometrical by nature.

Difference between strong and weak

The difference between the Strong Principle of Equivalence and the Weak Principle of Equivalence is that the strong equivalence states all the laws of nature are the same in a uniform static gravitational field and the equivalent accelerated reference frame, while weak equivalence states all the laws of motion for freely falling particles are the same as in a reference frame that is not accelerated.


The Weak Equivalence Principle states that objects fall at the same rate, provided that are much smaller than the attracting body and are freely falling.

The equivalence of inertial and gravitational mass states that mass determined by inertia is the same as mass determined by gravitation.

The Strong Equivalence Principle extends the equivalence of masses to state that observations of acceleration cannot be distinguished from gravitation.

Physics is amazing

Resources and references

Ron Kurtus' Credentials


Equivalence Principle - Laboratory Tests of Gravitational Physics

Equivalence principle - Wikipedia

Elevator, rocket, and gravity: the equivalence principle - Einstein online

Gravitation Resources


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