Presentation Transcript

1. Gravity

2. 11/22 1. How do you weigh an elephant using only a board, yourself and a fulcrum? 2. Why do you weigh less on a mountain? (universal gravitation)
3. 1. What factors does the force of gravity depend on? 2. How did newton change the way we see gravity?
4. 13.1The Falling Apple Newton reasoned that the moon is falling toward Earth for the same reason an apple falls from a tree—they are both pulled by Earth’s gravity.
5. 3/7 What comes to mind when you think of gravity?
6. 13.1The Falling Apple Newton understood the concept of inertia developed earlier by Galileo. He knew that without an outside force, moving objects continue to move at constant speed in a straight line. He knew that if an object undergoes a change in speed or direction, then a force is responsible.
7. 13.2The Falling Moon If the moon did not fall, it would follow a straight-line path.
8. 13.2The Falling Moon This original drawing by Isaac Newton shows how a projectile fired fast enough would fall around Earth and become an Earth satellite.
9. 13.2The Falling Moon Tangential velocity is the “sideways” velocity—the component of velocity perpendicular to the pull of gravity.
10. 13.2The Falling Moon If the force that pulls apples off trees also pulls the moon into orbit, the circle of the moon’s orbit should fall 1.4 mm below a point along the straight line where the moon would otherwise be one second later.
11. 13.3The Falling Earth Newton’s theory of gravity confirmed the Copernican theory of the solar system. Earth orbits the sun like the moon orbits the earth, constantly being pulled in, while tangential velocity is keeping the object in orbit.
12. Universal Gravitation Gravity acts everywhere in the universe. The force that causes an apple to fall is the same force that acts on the moon. What factors does gravity depend on
13. 3/10 1. What are the two things that cause the moon to orbit the earth? 2. What would happen to your weight, if your radius from the center of the Earth doubled?
14. 13.4Newton’s Law of Universal Gravitation Newton’s law of universal gravitation states that every object attracts every other object with a force that for any two objects is directly proportional to the mass of each object. Newton deduced that the force decreases as the square of the distance between the centers of mass of the objects increases.
15. 13.4Newton’s Law of Universal Gravitation The force of gravity between objects depends on the distance between their centers of mass.
16. 13.4Newton’s Law of Universal Gravitation Your weight is less at the top of a mountain because you are farther from the center of Earth.
17. 13.4Newton’s Law of Universal Gravitation The Universal Gravitational Constant, G The law of universal gravitation can be expressed as an exact equation when a proportionality constant is introduced. The universal gravitational constant, G, in the equation for universal gravitation describes the strength of gravity.
18. 13.4Newton’s Law of Universal Gravitation Philipp von Jolly developed a method of measuring the attraction between two masses.
19. 13.4Newton’s Law of Universal Gravitation A simpler method was developed by Philipp von Jolly. He attached a spherical flask of mercury to one arm of a sensitive balance. A 6-ton lead sphere was rolled beneath the mercury flask. The flask was pulled slightly downward. The gravitational force F, between the lead mass and the mercury, was equal to the weight that had to be placed on the opposite end of the balance to restore equilibrium. F, m1, m2, and d were all known, so the ratio G was calculated:
20. 13.5Gravity and Distance: The Inverse-Square Law Butter spray travels outward from the nozzle in straight lines. Like gravity, the “strength” of the spray obeys an inverse-square law.
21. 13.5Gravity and Distance: The Inverse-Square Law This law applies to the weakening of gravity with distance. It also applies to all cases where the effect from a localized source spreads evenly throughout the surrounding space. Examples are light, radiation, and sound.
22. 13.5Gravity and Distance: The Inverse-Square Law Gravitational force is plotted versus distance from Earth’s center.
23. 13.6Gravitational Field Field lines represent the gravitational field about Earth.
24. 13.7Gravitational Field Inside a Planet As you fall into a hole bored through Earth, your acceleration diminishes. The pull of the mass above you partly cancels the pull below.
25. 13.9Ocean Tides Newton showed that the ocean tides are caused by differences in the gravitational pull of the moon on opposite sides of Earth.
26. 13.9Ocean Tides This difference in pulls across Earth slightly elongates it. The oceans bulge out about 1 meter on average, on opposite sides of Earth. Because Earth spins once per day, a fixed point on Earth passes beneath both of these bulges each day, producing two sets of ocean tides per day—two high tides and two low tides.
27. 13.9Ocean Tides The two tidal bulges remain relatively fixed with respect to the moon while Earth spins daily beneath them.
28. 13.9Ocean Tides When the attractions of the sun and the moon are at right angles to each other (at the time of a half moon), neap tides occur.
29. 13.4Newton’s Law of Universal Gravitation The Universal Gravitational Constant, G What happens to F if One mass is half as much Both masses are twice as much. The distance is tripled Hint, substitute a one for every thing then do what the question is asking you to do.
30. 13.10Black Holes The size of the sun is the result of a “tug of war” between two opposing processes: nuclear fusion and gravitational contraction.
31. 13.10Black Holes When a massive star collapses into a black hole, there is no change in the gravitational field at any point beyond the original radius of the star. You will learn later that our some never becomes a blackhole…sorry
32. 3/10 What would happen to the earth if the sun collapsed into a black hole? Use the gravity equation to explain why a black hole is so powerful. A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying.
33. 13.10Black Holes The gravitational field strength near a giant star that collapses to become a black hole is the same before collapse (left) and after collapse (right).
34. 13.11What is up with Uranus? Until the middle of the last century astronomers were puzzled by unexplained perturbations (path changes) of the planet Uranus. The source of Uranus’s perturbation was uncovered in 1845 and 1846 by two astronomers, John Adams in England and UrbainLeverrier in France. Applying Newton’s law of gravitation, both astronomers concluded that there was a body beyond the orbit of Uranus. The planet Neptune was discovered.
35. Mu
36. Multiplying in Scientific Notation
37. Multiplying… The general format for multiplying is as follows… (N x 10x)(M x 10y) = (N)(M) x 10x+y First multiply the N and M numbers together and express an answer. Secondly multiply the exponential parts together by adding the exponents together.
38. Multiplying… Finally multiply the two results for the final answer. (2.41 x 104)(3.09 x 102) 2.41 x 3.09 = 7.45 4 + 2 = 6 7.45 x 106
39. Dividing in Scientific Notation
40. Dividing… The general format for dividing is as follows… (N x 10x)/(M x 10y) = (N/M) x 10x-y First divide the N number by the M number and express as an answer. Secondly divide the exponential parts by subtracting the exponent from the exponent in the upper number.
41. Dividing… Finally multiply the two results together to get the final answer. (4.89 x 107)/(2.74 x 104) 4.89 / 2.74 = 1.78 7 – 4 = 3 1.78 x 103
42. 13.11Universal Gravitation Recent evidence suggests the universe is not only expanding, but accelerating outward. It is pushed by an anti-gravity dark energy that makes up an estimated 73 percent of the universe. Twenty-three percent of the universe is composed of the yet-to-be discovered particles of exotic dark matter. The concepts of dark matter and dark energy will continue to inspire exciting research throughout this century.
43. Could you survive a plane crash? Why or why not? How could you test this? If you dropped a penny from a tall building could it kill a person?
44. What did you think of the final? How do you think you did on the forbidden kingdom final? Discuss number five Introduce astronomy presentations part two: gravity
45. What are some characteristics of a strong presentation? Which topic did you decide? Today Study your topic and generate two questions
46. What comes to mind when you think of gravity?
47. 13.2The Falling Moon This original drawing by Isaac Newton shows how a projectile fired fast enough would fall around Earth and become an Earth satellite.
48. What is the main idea behind your presentation? What is a future question you can ask based on your presentation? If you weight 160 pounds on the Earth’s surface what would be your weight if you climbed a ladder that was as long as the earths radius?
49. 13.2The Falling Moon The moon was already known to be 60 times farther from the center of Earth than an apple at Earth’s surface. The apple will fall 5 m in its first second of fall. Newton reasoned that gravitational attraction to Earth must be “diluted” by distance. The influence of gravity should be diluted to 1/60 of 1/60. In one second the moon should fall 1/(60)2 of 5 m, which is 1.4 millimeters.
50. 13.4Newton’s Law of Universal Gravitation Newton’s law of universal gravitation states that every object attracts every other object with a force that for any two objects is directly proportional to the mass of each object. Newton deduced that the force decreases as the square of the distance between the centers of mass of the objects increases. The magnitude of G is given by the magnitude of the force between two masses of 1 kilogram each, 1 meter apart: 0.0000000000667 newton. (In scientific notation: G = 6.67 × 10−11 N·m2/kg2)
51. Planet Semimajor axis (1010m) PeriodT (y) T2/a3(10-34y2/m3) Mercury 5.79 0.241 2.99 Venus 10.8 0.615 3.00 Earth 15.0 1 2.96 Mars 22.8 1.88 2.98 Jupiter 77.8 11.9 3.01 Saturn 143 29.5 2.98 Uranus 287 84 2.98 Neptune 450 165 2.99 Pluto 590 248 2.99 Kepler’s third law T2/ a3 period squared = axis cubed
52. What are two ways of reducing your weight without exercise or dieting?
53. What topic did you choose? What are some strong communication skills? What are some strong listening skills
54. 13.4Newton’s Law of Universal Gravitation The force of gravity between objects depends on the distance between their centers of mass.
55. 12/1/10 Think of two questions that your presentation will answer.
56. 12/2 warm up Is your presentation ready? What is one part that could use work? Take about 10 minutes to practice your explanations with your group members