2. FgFg agag mg g W Do you know the difference??

4. Newton’s Law of Universal Gravitation Every body in the universe attracts every other body with a force that is directly proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between the bodies.

5. Newton’s Law of Universal Gravitation When 2 masses are separated by a distance (r) r m1m1 m2m2 FgFg -F g The proportionality constant, G is called the universal gravitational constant. Its value in the SI system of units is, G = 6.67  10-11Nm 2 /kg 2. Cavendish link

6. The Law of Universal gravitation states that every object in the universe is attracted to every other object in the Universe! Greater the masses = greater the force of attraction Greater the distance = smaller the force of attraction

8. The more mass an object has, the greater its force of attraction. You are extremely attractive.

10. Sample Problems So you use the equation Fg = GMm/r 2 Fg = 6.67E-11*.05*.05/.8 2 Fg = 2.61E-13 N Find the gravitational attractive force between two identical 50 g spheres with centers.8 meters apart? G = 6.67x10 -11 N m 2 /kg 2

11. Weight and Gravitational Attraction. Fg = GMm/r 2 = 6.67E-11(5.98E24 )(75) / (6.37E6) 2 Fg = 737.46 N 1.Find the weight of a 75 kg person on the planet earth. 2. Find the gravitational force of attraction between a 75 kg person and the Earth? m earth = 5.98 x 10 24 kg r earth = 6.37 x 10 6 m W= 75 X 9.8=735 N

12. Acceleration Due to Gravity Calculate g for planet Earth at sea level.

13. Free-Fall Acceleration and the Gravitational Force Gravitational force: Thus : g is not constant as we move up from the surface of the earth!! G is a universal constant (does not change at all).

14. Example 6 The mass of the Hubble Space Telescope is 11,600 kg. Determine the weight of the telescope (a) when it was resting on the earth and (b) as it is in its orbit 598 km above the earth's surface. M earth = 5.98 x 10 24 kg R earth = 6.37 x 10 6 m G = 6.67 x 10 -11 N m 2 /kg 2 Answer: 114, 027 N =25,623 lbs 95,295 N = 21,414 lbs

16. Newton’s Law of Universal Gravitation: Conceptual Questions The moon and the Earth are attracted to each other by gravitational force. Does the more massive earth attract the moon with a greater force than the moon attracts Earth? Explain.

17. The force of gravity is an interaction between two masses. The force they exert on each other is an interaction pair. They are equal and opposite.

18. What happens to the gravitational force between two masses when the distance between the masses is doubled?

19. It is ¼ as much.

20. Jupiter has about 300 times the mass of Earth and about 10 times earth’s radius. Estimate the size of g on the surface of Jupiter.

21. g is 3 times greater

22. 3. If the Earth were twice as massive but remained the same size, what would happen to the value of G? g?

23. G is constant, g is double

24. Begin work on the first practice worksheet now.