physics 9th class Variation of g with altitude,altitude

Gravitational
field of earth

According to the Newton’s law of
gravitation, the gravitational force between a body of mass m and the Earth is
given by

where Me is the mass of the Earth and r
is the distance of the body from the center of the Earth

•The weight of a body is due to the
gravitational force with which the Earth attracts a body

•There is a field which exist all around
the earth which attracts the body toward the centre of earth this field is called
gravitational field of earth

•As we go away from centre of
earth  gravitational field decrease

FIELD
FORCE

Definition:

Non-contact force between bodies is
called field force

For Example gravitational pull of the
earth

The velocity of a body, thrown up, goes
on decreasing while on return its velocity goes on increasing. This is due to
the gravitational pull of the Earth acting on the body whether the body is in
contact with the Earth or not. Such a force is called the field force.

GRAVITATIONAL
FIELD STRENGTH:

In the gravitational field of the Earth,
the gravitational force per unit mass is called the gravitational field
strength of the Earth.

 At
any place its value is equal to the value of g at that point.

 Near the surface of the Earth, the
gravitational field strength is 10 N kg-1.