Newton proposed his law of universal gravitation, which states that every object in the universe attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. This law explained the force keeping the planets in orbit around the sun and the moon orbiting the Earth. Later experiments determined the proportionality constant in Newton's equation.

1. Newton’s Law of
Universal Gravitation

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.