10/16 Gee Whiz!

2. 10/16 Gee Whiz! • Tests are graded • Pick up UG WS. Due Monday • The S2 Team has decided that we will allow test corrections for those scoring less than a 70.

3. Is there gravity in space?

4. Why do objects fall at a rate of 9.8 m/s2? • What makes them fall? • Would this rate change on a larger planet? • Why?

5. History lesson Prior to Newton, the thought was that it was the natural tendency of objects to come to rest. Objects required a constant force to remain moving. NOT SO!!!!!!!!!!

7. Galileo’s Experiment

9. Forces Don't Keep Objects Moving. Forces Bring Objects to Rest

10. Galileo’s Principle of Inertia

11. Newton’s Laws and Forces • What are they? • Law of balanced forces • Law of unbalanced forces F = ma • Law of force pairs • What is force? • A push or a pull • Is ag (9.8 m/s2) a force? • No. It is acceleration in response to a force.

12. Newton’s Big Idea • Did Newton discover gravity? • NO! He discovered gravity is universal. Everything pulls on everything else in the universe in a way that only involves mass and distance. Gravity is not unique to earth.

13. Why was this so important?

15. The moon falls towards earth, just as the apple does. Why did he think this? • Why doesn’t it hit the earth?

16. Aristotle 384 BC • Ptolemy 127 AD • Copernicus 1543 • Galileo 1500s • Kepler 1609 • Newton 1669

17. Ptolemy vs Copernicus

19. Kepler

20. Kepler had determined planets had elliptical orbits in the 1600s. Kepler’s work was based on previous data gathered by the Dane, Tycho Brahe. • Newton was also investigating Galileo's Law of Inertia • Why did planets not obey Law of Inertia and move in straight line? • Circular and elliptical motion had to be accelerating in order not to travel in straight lines. • Since the object is accelerating, an invisible force must be present • The force is acting at a distance. • Concept of orbit of moon. • The force not limited to earth.

21. Yahtzee

24. No Gravity

25. Launch Speed less than 8000 m/sProjectile falls to Earth

26. Launch Speed less than 8000 m/sProjectile falls to Earth

27. Launch Speed equal to 8000 m/sProjectile orbits Earth - Circular Path

28. Launch Speed greater than 8000 m/sProjectile orbits Earth - Elliptical Path

29. By such reasoning, Newton came to the conclusion that any two objects in the Universe exert gravitational attraction on each other, with the force having a universal form.

30. Is there gravity in space? • Myth: there is no gravity in space • Fact: gravity is everywhere. • When you stand next to another person, there is gravitational force. Why don’t you feel it? • Your relative masses are too small so you only sense gravity in relationship to the earth. You feel this as weight. • Gravity is the weakest of the four fundamental forces. • The other three are electromagnetic, strong nuclear, and weak nuclear force.

31. Newton’s Law of Universal Gravitation: • Law of Universal Gravitation - there is a force of attraction between any two objects with mass. • The greater the mass the greater the force • The force decreases as the square of the distance increase

32. Newton’s Law of Universal Gravitation F = Force of attraction (N) G = 6.67 x 10-11 Nm2/kg2 m1= mass of object one (kg) m2 = mass of object two (kg) r = distance between the centers of the two objects (m)

33. G = 6.67 x 10-11Nm2/kg2 • me = 5.98 x 1024kg • re = 6.37 x 106m

34. Accepted Values • G = 6.67 x 10-11Nm2/kg2 This is the Gravitational Constant • me = mass of the Earth (5.98 x 1024 kg) • re = radius of the Earth (6.37 x 106 m)

35. How does mass affect Gravitational Force? • What happens to gravitational force if mass of one object is doubled? • Force is doubled • How would we graph mass vs force?

36. How does distance effect Gravitational Force? • What happens to gravitational force if the distance between objects is doubled? • The force decreases to 1/4th as much • How would we graph mass vs force?

37. Inverse Square Law

38. Ex. A What is the force of attraction between the Moon and Earth? Assume the distance from center of earth to center of moon = 384,403 km. Mass of moon is 7.35 x 1022 kg

39. Ex.A What is the force of attraction between the Moon and Earth? Assume the distance from center of earth to center of moon = 384,403 km. Mass of moon is 7.35 x 1022 kg (6.67 x 10-11 Nm2/kg2 )(5.98 x 1024 kg) )(7.35 x 1022 kg) F = [(3.84 x 108m)2] F = 1.98 x 1020 N

40. Example B: What is the force of attraction between you and your closest neighbor in this class? • 1 kg = 2.2 pounds • Assume you are spheres and your centers are 0.75 meter apart. • For two people at 150 pounds: (6.67 x 10-11 Nm2/kg2 )(68.2kg) )(68.2 kg) F = (0.75m)2 F = 5.52 x 10 -7 N

41. What is the second law of motion?

42. What is the third law of motion?

43. Example C: What is the force of attraction between you and the earth?1 kg = 2.2 pounds What would you use for r? The radius of the earth: 6.38 x 106 m (6.67 x 10-11 Nm2/kg2 )(5.98 x 1024 kg) )(68.2 kg) F = [ (6.38 x 106 m)2 ] What is the force of the earth’s pull on you? F = 668 N What is the force of your pull on the earth? F = 668 N (Force Pairs)

44. The force between you and the earthF = 668N m = 68.2 kg • Most of the force is dependent upon? • Mass of the earth • Do you know what else this value describes? • Your weight! • F = ma • Use your mass and F between you and earth. Solve for a. • Did you get 9.8 m/s2 ? WEIRD!!!!!

45. What is the difference between mass and weight • What is the unit for mass in metric? • What is the unit for weight in metric? • What is the unit for mass in standard? • What is the unit for weight in standard?

47. What is a Field? • A field is a region in which a suitable detector experiences a force. • A suitable detector for a gravitational field is an object with a very small mass. • There are other “fields” besides gravity. Can you think of any others?

48. Applications of the Law of Universal Gravitation The inverse square law Calculate the gravitational field, ie. “g” In relation to earth, this is only 9.8 m/s2 when on the surface of the earth. When doing calculations where objects are falling out of buildings use 9.8m/s2 because it is “close enough” but if objects are in the atmosphere we must account for distance Would your weight be greater at sea level or on the top of Mt. McKinley?

49. G vs g • How is G different from g? • G is a constant. It is the same everywhere in the universe. It describes the proportionality between force, distance, and mass. • g is changing. It is a measure of the local gravitational field (equivalent to the local acceleration due to gravity or ag). On earth it is 9.8m/s2. Referred to as gravitational acceleration or gravitational field. (Also can be measured in N/kg)

50. Acceleration due to Gravity • When the weight of the satellite (msg) is set equal to the gravitational attraction between the earth and the satellite (Gmsme/d2), the mass of the satellite will cancel out telling us that the acceleration due to gravity at any point can be calculated. • As distance between the satellite (ms) and larger mass (me) increases, what happens to g?