Universal Gravitational Law
Gravitational attraction between two objects vs. mass of the objects and the distance between them.
The gravitational attraction between two objects depends upon the mass of the objects and the distance between them. This relationship is often called the "Universal Law of Gravitation" and can be expressed as
F = k _{ G } m _{ 1 } m_{2}/ r^{2}(1)
where
F = gravitational force (N)
k _{ G } = 6.668 10 ^{ 11 } (Nm^{2}/kg^{2}) = the Universal Gravitation Constant
m = mass of object (kg)
r = distance between objects (m)
Example  The Gravitational Force (Weight) Acting on a Person on Earth's Surface
The gravitational force (or weight ) acting on a person with mass 70 kg on the earth's surface ( 6.37 10 ^{ 6 } m from the earth's center) can be calculated as
F = (6.668 10 ^{ 11 } Nm^{2}/kg^{2}) (5.98 10 ^{ 24 } kg) (70 kg) / (6.37 10 ^{ 6 } m)^{2}
= 688.1 (N)
 5.98 10 ^{ 24 } (kg) = mass of earth
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