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- The Moon makes a revolution about the Earth in 27.3 days
- Distance of Moon from Earth is about 3.85 * 10 ^ 5 km
- Newton calculated the acceleration of the moon directed towards Earth as 0.0027 m / s ^ 2

#### Heliocentric theory

- Earth and other planets moved in perfect circles around the Sun, located at the center of these circles. This theory was proposed by Copernicus.

#### Geological theory

- The Earth is stationary and is at the center of the universe with the Sun, Moon, planets and stars revolving around the Earth. It was proposed by Ptolemy.

#### Newton’s universal law of gravity (G)

Everyone in the universe attacks every other body with a force that is directly proportional to the product of their mass and universally proportional to the square of the distance between them. The force acts along a line joining two bodies.

**Examples of gravity meters**

- Converted
- Oscillator or vibrator
- Rotator

#### Centripetal force

A particle that continuously acts on a particle when initially moving with a linear velocity, it travels along a circular path known as the centrifugal force.

#### Examples of Centripetal Force

- The Earth moves around the Sun due to the gravitational force of attraction between them. Here the force of gravity acts as the centripetal force. A uniform gravitational force of attraction provides the necessary focal force for a satellite revolving around a planet.

#### key points

- The basis of Newton’s law of gravitation: Kepler’s law
- The force acts on a 400-gram stone: 3.92 N.
- G does not depend on body mass