Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 1 The Ptolemaic model of the universe made which assumptions? I) The Sun is at the center of the Universe II)All heavenly bodies move in combinations of perfect circles III)The Earth is at the center of the Universe IV)The stars never move a)I and IV b)I, II, and IV c)III only d)II and III e)II, III, and IV

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 2 Announcements: Exam #1: Thursday, Feb 22 We might not get through enough material for you to do HW #4. Stay tuned….

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 3 Review Cosmology of ancient Greeks Eudoxes, Ptolemy Retrograde motion, epicycles Copernicus Galileo Proved heliocentric model of solar system Today Discoveries of Galileo Newton’s Law of Gravity

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5 Astronomy During the Renaissance

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 6 The Geocentric vs. Heliocentric Debate De Revolutionibus Orbium Coelestium, Nicolai Copernicus, 1543

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7 Advantages of the Geocentric Model 1.Earth was not thought to be a “celestial” body. Non-luminous sphere of mud/rock Birth, change, destruction 2.Earth “feels” stationary. Wouldn’t clouds, air, birds, etc. be left behind were Earth moving?! 3.No stellar parallax could be measured Hipparchus tried very hard! (150 BC)

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 9 Stellar Parallax Parallax angle of the nearest star is less than 1/3600 of one degree. Ancient astronomers tried to measure parallax via careful naked-eye observations but failed. Finally detected in 1830 by F. Bessel using telescope.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 10 A species living on Europa uses telescopes similar to ours to measure parallaxes of stars in our galaxy. Which of the following statements best describes their results: a. Because they are further from the Sun, they are only able to measure parallax angles to the closest of stars. b. Because they have a longer baseline, they are able to measure parallax angles to more distant stars. c. Because they have a longer baseline, they are only able to measure the parallax angles to the closest of stars.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 11 N. Copernicus ( ): G. Galilei ( ): As the “giver of life”, he believed Sun should be placed at the center of the Universe. Believed that the Ptolemaic model had become too clumsy and complicated. Conducted experiments on the nature of motion. Observed celestial objects with telescope.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 12 Galileo’s Findings More stars! Is the universe infinite? Moon craters Earth-like surface Sun spots Celestial bodies not perfect! Moons of Jupiter A mini solar system? Phases of Venus Ptolemaic model could not explain.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 13 Venus’ cycle of phases Figure 1.29

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 14 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15 Isaac Newton ( ) Laws of Motion Law of Gravity Calculus Nature of Light

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 16 Vocabulary: inertia velocity acceleration net force

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 17 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 18 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. Why? Because objects have “inertia ”

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 19 Net force = sum of all forces: Here, we say that the NET force is zero! The box stays at rest. There is no change in its state of motion – no net force is acting on it.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 20 Force and inertia Natural state of motion is at a constant speed, in a straight line. Ball wants to travel in a straight line, but the string continuously pulls it back toward the center of the circle.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 21 Uniform Motion: same speed, same direction

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 22 Acceleration: a change in speed

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 24 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

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