1) Isaac Newton proposed a law of universal gravitation in 1666 that states any two objects attract each other with a gravitational force proportional to the product of their masses and inversely proportional to the square of the distance between them. 2) The law explains that gravity is what keeps planets in orbit around the sun and the moon in orbit around Earth. 3) Henry Cavendish experimentally determined the proportionality constant G in 1798, known as the gravitational constant, which is equal to 6.67 x 10-11 N m2 / kg2.

1. Newton’s Law of
Universal Gravitation
Physics
Mr. Berman

2. Isaac Newton
 1666, England (45 years
after Kepler).

3. Questions
 If the planets are orbiting the sun , what force is
keeping them in orbit?
 What force keeps the moon in its orbit?
 Could the force of gravity be universal?

4. Newton’s Law of Universal
Gravitation
 Any two objects attract each other with a
gravitational force, proportional to the
product of their masses and inversely
proportional to the square of the distance
between them.
 The force acts in the direction of the line
connecting the centers of the masses.

5. Newton’s Law of Universal
Gravitation
http://scienceblogs.com/startswithabang/upload/2009/07/meet_our_second_moon/400px-NewtonsLawOfUniversalGravitation.svg.png

6. Why does the moon not fall straight
down onto the earth?

7. Henry
Cavendish’s
experiment
determined the
proportionality
constant
G
in 1798.
http://www.newscientist.com/data/images/archive/1639/16390101.jpg

8. The Value of G.
G= 6.67 x 10-11 N m2 / kg2

9. Change of
Gravitational
Force with
Distance
 Law of universal
gravitation is
known as an
inverse square
law.

10. Problem 1
 Two spheres of mass 35kg are 60m apart.
A) What force does one exert on the other?
B) If the mass of one is tripled and the radius
is quadrupled how does the force change?

11. Problem 2
 Two spheres of equal mass have a force
of gravity of 7x10-9 exerted on each other.
If the distance between them is 7m, find
the mass.

12. Problem 3
 Find the value of the gravitational
acceleration g. The mass of the earth is
6.0 x 1024kg.