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M
g  G , (4.10)
r 2
when r  R
The potential (energetic characteristic) of gravitational field is
defined as the ratio of the potential energy W of the material point with
p
mass m test at that point to the mass m test
E p
 . (4.11)
m test
The potential of gravitational field of material point with mass m on

arbitrary distance r is equal to
m
  G (4.12)
r

4.3 Questions

1.What does Kepler's laws state?
2.What's gravitation or gravity?
3.What does Newton's law of universal gravitation state?

4.What's physical meaning of the gravitational constant ?
5.How did Cavendish "weight" the Earth?
6.What's the intensity of gravitational field?
7.How does the gravitational field of spherical distribution of matter

look?
8.What's potential of gravitational field?

4.4 Problems
A spaceship travels from the Earth directly towards the Moon .At
what distance from the centre of the Earth to the Moon gravitational
forces are equal? The distance from the Earth to the Moon is

, 3 844 10 8 m.Mass of the Earth M  , 5 976 10 24 kg , mass of the
E
Moon M , 7 35 10 22 kg .
M 
Solution
The Earth attracts spaceship

with the force
m  M E
F  G .
1
x 2

Figure 5.1 At the same time the Moon

attracts spaceship with the

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