Page 45 - 4167

large and small spheres turn the system through a small angle  ,
thereby moving the reflected light beam along the scale on the double
angle .

Using of an extremely fine fiber, the deflection of the mirror
may be made sufficiently large so that the gravitational force can be
measured quite accurately. After that Cavendish compared this force

with gravitational force of the Earth and ipso facto defined mass of
the Earth. Therefore Cavendish experiment is often called as
"weighting of the Earth" . And only thereafter due to the mass of the
Earth gravitation constant was calculated. The gravitation constant,

measured in this way, is found to be

N  m 2

11
G  , 6 67 10 .
kg 2
4.2. Gravitational Field. The Intensity of Gravitational Field.
Potential of Gravitational Field

The gravitational interaction of bodies is realized through the
gravitational field. Any body is a source of the gravitational field. This
field displays itself in such manner that any other body placed in it is

acted upon by the force of gravity that is proportional to the mass of this
body. The gravitational field is characterized by the field intensity.
The intensity g of gravitational field at any point is defined as the
ratio of the force F acting on a small test material point with mass

m test at that point to the mass of this material point .

 F
g  (4.5)
m test

The intensity g of gravitational field is force characteristic of this

field and as follows from unit of intensity g of gravitational field is
m i.e. unit of acceleration.
s 2
Let us consider some examples of intensity of gravitational field
1.Gravitational field of material point, i.e. we should solve the next

problem:
What's intensity g of gravitational field of material point with mass
m on arbitrary distance r ?

If on this position to place a small test material point with mass m test
and define force that acts on this material point(fig.4 .3)then

44