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Lecture series from Conceptual Physics, 8 th Ed..

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Presentation on theme: "Lecture series from Conceptual Physics, 8 th Ed.."— Presentation transcript:

1 Lecture series from Conceptual Physics, 8 th Ed.

2 Copernicus, Brahe, and Kepler p142 Speculated that the sun was the center of the solar system. Thought he would gather some data before shooting off his mouth about his heliocentric ideas. Which was probably a good idea seeing as how his nose had already been cut off in a duel. ( He was rich and threw really gnarly parties so he got away with a lot.) Used Brahes data to develop mathematical models of the motions of the planets.

3 Keplers Laws p143 First he translated Brahes data from Earth based reference to what would be seen by a stationary observer outside the solar system. His laws of planetary motion are: 1. Planets move in ellipses. 2. The equal areas thing. 3. T 2 proportional to R 3 Fantastic stuff, but he didnt know about gravity, didnt apply inertia, didnt know why ellipses… BUT, he was right because he had good data.

4 Newtons Law of Universal Gravitation p144 -knew that inertia kept the planets moving. -the force acting on the planets caused them to curve. -from looking at Keplers stuff, he knew the force emanated from the sun. (He deduced gravity.) -he also deduced that the forced decreased with the square of the distance. -the apple thing reminded him that gravity acts between masses and therefore objects in orbit are falling around their primaries. Here it is gang!! F g = Gm 1 m 2 d2d2

5 The Universal Gravitational Constant, G p145 G = F d 2 m1m2m1m2 = 6.67x Nm 2 /kg 2 An interesting example: How much does the earth mass? From F=Gm e m o /d 2 m o g = Gm e m o /d 2 So, m e = g d 2 G = (9.8)(6.4x10 6 ) 2 (6.67x ) = 6.0x10 24 kg Imagine an object on the surface of the earth.

6 Gravity and Distance: The Inverse-Square Law p147 Weight decreases as person climbs.

7 Weight and Weightlessness p149 Fig. 8.7 Your weight equals the force with which you press against the floor.

8 More Weightlessness In fact. Gravity does not produce weight! The floor produces weight. Both people are in a gravitational field.

9 Ocean Tides p150 Equal forces to the right means Jell-O ball stays spherical. Forces shown here cause left side to lag behind. The left side is further from moon and is not pulled as strongly toward moon.

10 More on Tides This planet has bigger tides because delta F is greater. Smaller delta F means smaller tides. Delta F refers to the difference in forces at the front and back of the planet. F = G m m / d 2

11 Spring tides : Neap tides : The earths tilt means that this person has a lower high tide than this person. Tides in the Earth and the atmosphere work the same way.

12 Tides on the Moon p154 The key thing is that the moon acts like a pendulum. This part of the moon swings back and forth trying to line up with the Earth. Why does the moon always face us?

13 The Gravitational Field Inside a Planet p155 First, the outside field lines: Now, the inside: Last, the in and the out -side

14 Einsteins Theory of Gravitation p157 Albert says that the moon is NOT pulled to the Earth. The moon curves because the surface it travels on is tilted toward the Earth.

15 Black Holes p157 Their gravitational field is so strong that even light can not escape! A collapsing star with Superman standing on its surface. Because of F=Gmm/d 2 When the star collapses to ½ its radius, Supys weight quadruples. When the star crushes its matter to a few hundred kilometers, that may be the last we see of it. Only gravity, charge and angular momentum remain. Things orbit it and spiral inward.

16 Universal Gravitation p 159 As far out as we can see, matter seems to obey Newtons law of gravitation: F=Gmm/d 2. Neptune and Pluto were discovered by using the law. The activities of distant galaxies seem to obey the law. BUT, the universe is expanding too fast!! To be continued.

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