1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 1 The ball moves over my head at a constant speed as shown. Is the ball accelerating? Is there a net force acting on the ball? a.Yes. Yes. b.No. No. c.Yes. No. d.No. Yes

2. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 2 Announcements: Exam #1: Tuesday, Feb 27 Chapter 1, Essay 1, Chapter 2 HW #4: due Thursday

3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 3 Review Galileo’s contributions to Astronomy Parallax: definition Newton’s Laws of Motion Today Newton’s Laws of Motion (cont) Newton’s Law of Gravity

4. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 4 Stellar parallax

5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 5 Gravity and Motion “… the shuttle blasts off … Then comes the tremendous pressure of three G’s and the sudden release into weightlessness as the ship leaves the gravitational field behind…” - from The Arizona Republic

6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 6 Vocabulary Review: inertia: quantified as mass velocity: speed + direction acceleration: denotes a change in velocity net force: sum of all forces (includes direction)

7. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7 Newton’s First Law of Motion: An object continues in a state of rest or in a state of uniform motion at a constant speed along a straight line unless compelled to change that state by a net force.

8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 8 Newton’s 2 nd Law of Motion: The amount of acceleration (a) produced by a force (F) depends on the mass (m) of the object being accelerated. Mathematically: F = m×a Alternatively: a = F/m

9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 9 Acceleration

10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 10 Gravity, force, and mass G=6.67×10 -11

11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 11

12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 12 Book on top of paper: which hits the ground first? a) book b) paper c) both hit at same time Paper on top of book: which hits the ground first? a) book b) paper c) both hit at same time

13. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 13 Paper versus steel ball: which hits the ground first? a) paper b) steel ball c) both hit at same time Dropped ball versus canon: which hits the ground first? a) dropped ball b) canon c) both hit at same time

14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 14 Acceleration due to Earth’s gravity is the same for all falling objects.

15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15 Question: A linebacker and a kitten are put into space far from any other object. How do the gravitational forces each feels compare? How do their accelerations compare? a. Linebacker feels larger force, but accelerates less. b. Kitten feels larger force and accelerates more. c. Both feel same force, but kitten accelerates more.

16. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 16 The linebacker and the kitten on Earth: How do the forces that they feel (due to the Earth’s gravity) compare? How do their accelerations compare if they both jump off a table? a.Forces equal, kitten accelerates more. b.Larger force on linebacker, accelerations equal. c.Forces equal, accelerations equal. Example

17. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 17 Weight: Weight is NOT the same as “mass”. Weight is equivalent to the gravitational force the Earth exerts on your body.

18. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 18 Are you weightless on the Moon? a) yes b) no c) depends Is there “gravity” on the Moon?

19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 19 Weight versus Apparent Weight:

20. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 20 The Moon Doesn’t Fall to the Earth!!! Why Not?

21. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 21 If I could give the Moon a larger velocity, what would happen?

22. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 22

23. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 23 Escape velocity is speed to beat gravity Figure 2.9 11.2 km/s 25000 mph!!

24. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 24 What’s wrong with this…. “… the shuttle blasts off … Then comes the tremendous pressure of three G’s and the sudden release into weightlessness as the ship leaves the gravitational field behind…” - from The Arizona Republic