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where the "gravitational mass" is likewise a characteristic

constant for the body. From these two relations follows:

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If now, as we find from experience, the acceleration is to be

independent of the nature and the condition of the body and

always the same for a given gravitational field, then the ratio

of the gravitational to the inertial mass must likewise be the

same for all bodies. By a suitable choice of units we can thus

make this ratio equal to unity. We then have the following law:

The gravitational mass of a body is equal to its inertial mass.