Page 4 - Force 10

Unit 1: Gravitational force 1

Gravitational field: The region of space around F = G × 2 ………(iii) [where G is
1
2

a mass where another mass experiences the known as the universal gravitational constant
gravitational force is called gravitational field.
2
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and its value is 6.67 × 10 Nm /kg .
2
Gravitational field intensity: The gravitational
force experienced by a unit mass placed at a
point in the gravitational field is called
gravitational field intensity.

❖ The effect of gravitation can be observed
more on liquid than on solid. Hence we
see tides in the sea due to the gravitation
of the moon & the sun.
th
❖ The gravity of moon is only (1/6) of the
earth because of less mass. So, it can’t
hold the layer of air around it & the air
escapes away from the center of the moon
then there is no atmosphere in the moon.

Newton law is universal:
Formulae:
❖ It is applicable for all the objects within
the entire universe.  =

❖ This law is applicable for the micro  =
objects like electrons to macro objects like

huge stars.  =

Newton’s law of gravitation: = ( + )
 = ( − )
Let us consider two objects A and B having
masses m 1 and m 2 respectively are separated by Where,
g= acceleration due to gravity
a distance d. If the force of attraction between is F=Gravitational force between two objects
F, then according to the law of gravitation, m1, m2, m =mass of an object
M= mass of planet or satellite
F ∝ × ………….. (i) ( when d is R= radius of planet or satellite
2
1
kept constant) u=initial velocity
1
F ∝ ……………….. (ii) (when m is t=time taken.
2 d=distance between two objects
kept constant) h=height
Combining equations (i) and (ii), we get,

1
F ∝ × 2
2

Do you know?
The force of gravity 100 km (60 miles) above the earth is just 3% less than on the Earth’s surface.