Universal Gravitation
Gravitational Acceleration
All objects on the earth are pulled by universal gravitation toward the center of the earth.
Force to which the earth pulls the object is called gravity.
The object in the vicinity of the ground is attracted to the earth by gravitation.
Gravitation can be expressed by two kinds of expressions.
| The second law of movement | F =mg |
| Law of universal gravitation | F =GMm/r2 |
Where, gravity is F, the mass of the object is m, the mass of the earth is M, the radius of the earth is r, the acceleration caused in the object is a, the universal gravitation constant is assumed to be G.
The height of the object in the vicinity of surface of the earth is small enough compared with radius r of the earth (about 6371km).
Therefore, the distance from the center of the earth to the object can be substituted by radius r of the earth.
It can be considered that GM/r2 is constant as long as it is on the earth.
When you compare the above-mentioned two expressions
GM/r2=g is understood.
Because g is an acceleration caused by gravitation, it is called, "Gravitational acceleration".
g doesn't depend on the mass of the object as understood from the expression.
G is an amount almost equal to the object in the vicinity of the surface of the earth.
The earth is globular that collapses (Low latitudes swell). In addition, an internal density is not even.
Therefore, there are a few differences in gravitational acceleration by the place.
Two objects reach the ground at the same time when dropping it from equal height at the same time. (law of Galileo's Ototai)
This is natural. The reason for g is constant if it is the same place.
The value of g is about 9.8 m/s2
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