Mass [3]
Inertial Mass and Gravitational Mass
The object is not moved easily by mass large.
And, big universal gravitation is caused by mass large.
Saying will have two sides in mass.
The first is a side as the source of universal gravitation.
Universal gravitation is force to act between objects, and to attract each other.
The magnitude of the force is proportional to the product of each mass of the object.
In a word, the larger each mass is, larger universal gravitation is.
The mass seen in this aspect is especially said, "Gravitational mass".
The magnitude of "Gravitational mass" decides the magnitude of universal gravitation.
The second is a side as the magnitude of inertia.
The object of big mass is not moved easily.
However, a small object of mass can move by less force, and change the direction of movement.
This is the second law of the movement.
The mass seen in this aspect called "Inertial mass".
For instance, let's assume that object A is here.
It is "Gravitational mass" to be calculated measuring the gravitation between A and other objects B.
Adding constant force to A, measuring the acceleration, and being calculated are "Inertial mass".
The gravitational mass and the inertial mass are based on different essence as understood from the above-mentioned.
An arbitrary object will have both the gravitational mass and the inertial mass.
Therefore, when the gravitational mass and the inertial mass are measured respectively, you are sure obtain a different value.
However, it is confirmed that the value of the gravitational mass and the inertial mass is corresponding by the accuracy of 10< sup>9 by the experiment though it is a quite different concept.
There is a discussion "Are the gravitational mass and the inertial mass really equal?" for a long time.
It is thought that both are corresponding today.
Einstein assumed that both were not able to distinguish, and progressed general theory of relativity.
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