1. Newton’s Laws of Motion
Chapter 4 Lesson 2

2. Newton’s Law of Universal Gravitation

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

4. 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?

5. 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.

6. Newton’s Law of Universal Gravitation

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

8. Henry Cavendish’s experiment determined the proportionality constant G in 1798.

9. The Value of G.
G= 6.67 x N m2 / kg2

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

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

12. 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.

13. Problem 3
Find the value of the gravitational acceleration g. The mass of the earth is 6.0 x 1024kg and its radius is 6.38 x 106 m.