1. © 2010 Pearson Education, Inc. Newton’s third law of motion: For every force, there is always an equal and opposite reaction force.

2. © 2010 Pearson Education, Inc. Clicker Question How does the force the Earth exerts on you compare with the force you exert on it? A.Earth exerts a larger force on you. B.You exert a larger force on Earth. C.Earth and you exert equal and opposite forces on each other.

3. © 2010 Pearson Education, Inc. Clicker Question How does the force the Earth exerts on you compare with the force you exert on it? A.Earth exerts a larger force on you. B.You exert a larger force on Earth. C.Earth and you exert equal and opposite forces on each other.

4. © 2010 Pearson Education, Inc. What keeps a planet rotating and orbiting the Sun?

5. © 2010 Pearson Education, Inc. Conservation of Angular Momentum The angular momentum of an object cannot change unless an external twisting force (torque) is acting on it. Earth experiences no twisting force as it orbits the Sun, so its rotation and orbit will continue indefinitely. Angular momentum = mass x velocity x radius

6. © 2010 Pearson Education, Inc. Angular momentum conservation also explains why objects rotate faster as they shrink in radius.

7. © 2010 Pearson Education, Inc. Where do objects get their energy? Energy makes matter move. Energy is conserved, but it can: –transfer from one object to another –change in form

8. © 2010 Pearson Education, Inc. Basic Types of Energy Kinetic (motion) Radiative (light) Potential (stored) Energy can change type, but cannot be created or destroyed.

9. © 2010 Pearson Education, Inc. Clicker Question A rock held above the ground has ___. A.Radiative energy B.Kinetic energy. C.Potential energy D.Thermal energy

10. © 2010 Pearson Education, Inc. Clicker Question A rock held above the ground has ___. A.Radiative energy B.Kinetic energy. C.Potential energy D.Thermal energy

11. © 2010 Pearson Education, Inc. Mass-Energy Mass itself is a form of potential energy: E = mc 2 A small amount of mass can release a great deal of energy. Concentrated energy can spontaneously turn into particles (for example, in particle accelerators).

12. © 2010 Pearson Education, Inc. Conservation of Energy Energy can be neither created nor destroyed. It can change form or be exchanged between objects. The total energy content of the universe was determined in the Big Bang and remains the same today.

13. © 2010 Pearson Education, Inc. What determines the strength of gravity? The universal law of gravitation: 1.Every mass attracts every other mass. 2.Attraction is directly proportional to the product of their masses. 3.Attraction is inversely proportional to the square of the distance between their centers.

14. © 2010 Pearson Education, Inc. Clicker Question If you double the distance between two objects, the gravitational force between them __. A.doubles B.quadruples. C.is ½ the original force. D.is ¼ the original force E.Remains the same.

15. © 2010 Pearson Education, Inc. Clicker Question If you double the distance between two objects, the gravitational force between them __. A.doubles B.quadruples. C.is ½ the original force. D.is ¼ the original force E.Remains the same.

16. © 2010 Pearson Education, Inc. Clicker Question If you double the mass of one of the objects, the gravitational force between them __. A.doubles B.quadruples. C.is ½ the original force. D.is ¼ the original force. E.Remains the same.

17. © 2010 Pearson Education, Inc. Clicker Question If you double the mass of one of the objects, the gravitational force between them __. A.doubles B.quadruples. C.is ½ the original force. D.is ¼ the original force. E.Remains the same.

18. © 2010 Pearson Education, Inc. Clicker Question Lastly, if you double the mass of both objects, and double the distance between them, the gravitational force between them __. A.doubles B.quadruples. C.is ½ the original force. D.is ¼ the original force. E.Remains the same.

19. © 2010 Pearson Education, Inc. Clicker Question Lastly, if you double the mass of both objects, and double the distance between them, the gravitational force between them __. A.doubles B.quadruples. C.is ½ the original force. D.is ¼ the original force. E.Remains the same.