Gravitational Field

Field is a region of space that can be mapped with lines of force or with lines of potential.

Gravitational Field is a region of space where a mass experiences a force.

Gravitational Field Strength is the force per unit mass acting on a small mass placed at a point in the gravitational field.

g = F/m

Newton’s Law of Gravitation - the force of attraction between two particles is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

F= GMm/r2

Gravitational Potential is the work done per unit mass in bringing a point mass from infinity to that point.

φ = W/m

Geostationary orbit refers to a circular orbit around the earth on which a satellite would appear stationary to an observer on the Earth’s surface.

Geostationary Satellite – one which is above the same spot above the Earth at all times.

A geostationary satellite

- must be placed vertically above the equator,

- must move from west to east, has a period of 24 hours. Same as the period of the earth as it turns about its axis.

- is placed in a orbit at a distance of 4.23 x 107 m from centre of Earth. Only one geostationary orbit as period T is only dependent on radius r.

The centripetal force which keeps a satellite in orbit round the earth is the gravitational force of attraction between them.

Hence mv2/r = GMm/r2 or mrω2 = GMm/r2

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