1. Newton’s law of universal gravitation
Newton did not discover gravity he discovered universal gravitation. Explain.
He discovered that everything pulls on everything else within the universe. He called this phenomenon: Universal gravitation.
The force involved is called; ____________________
Universal gravitational force is determined by the masses of objects involved and distance between the objects involved.

2. Force of gravity between objects and masses.
For any two objects with masses m1 and m2, the force between them in directly proportional to the product of their masses.
That is;
D = ? m1 m2

3. Force and the distance between objects.
The universal gravitational force is inversely proportional to the square of the distance between objects.
That is;

4. symbolic expression of the law of universal gravitation

5. Statement of the Law
Force between two masses is directly proportional to the product of the two masse and inversely proportional to the square of the distance between them.

6. The proportionality form of the law

7. Universal gravitational constant ‘G’
G= Universal gravitational constant
What does the size of G, which is a very small number say about the force of Universal gravity?
It explains why gravitational force between objects is the weakest force.
We do not feel it between small objects.
The force is only felt if one of the masses is large enough, say like the planets.

8. weight of an object
The weight of an object on Earths surface equals the gravitational force between that object and the earth. True/False.
True. The distance between the object and the earth is just the radius of the earth.

9. Example
Two masses 6kg and 5 kg are separated by a distance of 2 m, calculate the gravitational force between them.

10. Example 2
The gravitational force between the moon and the earth is 2.0 x 10²º N What would this force be if;
The earth was twice as massive?
The distance between them was halved?

11. Classwork/homework
Textbook Page 180 # 1-14

12. Warm-up
The gravitational force between the moon and the earth is 2.0 x 10²º N What would this force be if;
The earth was half as massive?
The distance between them was doubled?

13. Falling apple
Falling apple because of universal force of gravity between the apple and the earth

14. Falling moon?

15. Falling moon?
Why doesn’t the moon really fall onto the earth?

16. Falling moon?
The moon actually falls but not on the earth. It falls around the earth.
The moon has a tangential velocity of about 8 km/second which allows it to fall around the earth.

17. Tangential velocity
Tangential velocity is the linear velocity of an object that is revolving around another object.
Tangential velocity (Vt) F

18. Incase the moon stopped moving?
The Universal force of gravity pulls the moon towards the center of the earth. Therefore,
Incase the moon stopped moving, it would fall straight down on the earth, due to this force.

19. Weight of an object on Earths surface
The weight of an object on Earths surface equals the gravitational force between that object and the earth. Explain

20. Acceleration due to gravity ‘g’
What is the formula for finding acceleration due to gravity ‘g’ of an object?

21. Class work
Textbook page 180, # 15-30