Newtons Law of Gravitation

1. Newton’s Law of
Universal Gravitation

2. Outline
 Who Found It?
 The Statement of the Law
 Gravity Near the Earth’s Surface
 Geophysical Applications
 Satellites

3. Who Found It?

4. The Statement
of the Law
 Magnitude: Every particle in the universe
attracts every other particle with a force that is
proportional to the product of their masses and
inversely proportional to the square of the
distance between them.
 Direction: This force acts along the line joining
the two particles.
1 2
2
m m
F G
r

11 2 2
6.67 10 /
G N m kg

  

5. Gravity Near the Earth’s Surface
1 2
2 2
E
E
m m m m
F G G mg
r r
  
2
E
E
m
g G
r

2
24
5.98 10
E
E
gr
m kg
G
  

6. Some Geophysics

7. Some Geophysics: Applications
Variation in g: Gravity Anomalies
To investigate
 the structure of the Earth’s crust
 mineral deposit
 oil exploration
Some examples
 mineral deposit
 oil exploration

8. Satellites
 What keeps a satellite up?
Its high speed
 How they move?
2
2
sat E sat
m m v
G m
r r


9. Moon:
Special Satellite



22
:7.35 10
Mass kg

8
tan :1.5 10
Dis ce km

: 29.5306
Period days

10. Earth: the Satellite of the sun

11. Summary
 a force “acting at a distance” even though
there is no contact
 a useful tool to explore in space