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# Universal Gravitational Law

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

## Related Topics

### • Dynamics

Motion - velocity and acceleration, forces and torque.

### • Mechanics

Forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more.

## Related Documents

### Acceleration of Gravity and Newton's Second Law

Acceleration of gravity and Newton's Second Law - SI and Imperial units.

### Acceleration of Gravity vs. Latitude and Elevation

Acceleration of gravity due to latitude and elevation above sea level.

### Center of Gravity

A body and the center of gravity.

### Center of Gravity and Buoyancy

Stability - the center of gravity vs. the center of buoyancy.

### Density vs. Specific Weight and Specific Gravity

An introduction to density, specific weight and specific gravity.

### Mass vs. Weight

Mass vs. weight - the Gravity Force.

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