Hobson Physics: Concepts & Connections 4e

Chapter 1 review questions Observing the Night Sky 1. What two reasons does this chapter give for studying science? 2. What is physics? 3. Distinguish astronomy from astrology. 4. What astronomical objects can you normally see in the night sky? Describe their motion as seen from Earth. Ancient Greek Theories 5. What did the Pythagoreans believe, and how did these beliefs influence the development of science? 6. According to the earliest Greek theory, the planets orbit Earth in uniform circular motion. In what way does this theory disagree with simple observations made without telescopes? 7. Give two observational reasons for believing that Earth is curved rather than flat. 8. How does Ptolemy’s theory explain the retrograde motion of the planets and the fact that planets are brighter during retrograde motion? 9. Did Ptolemy’s theory agree with the quantitative observations known in Ptolemy’s time? How were these observations made? Copernicus’s Theory 10. “Copernicus rejected Ptolemy’s theory because it disagreed with the data, and he proposed a new sun-centered theory that did agree with the data.” True or false? Explain. 11. Use Copernicus’s theory to explain the retrograde motion of the planets and the fact that they are brighter during retrograde motion. 12. Why did Copernicus propose his theory? 13. State at least one plausible argument against the notion that Earth moves around the sun. 14. How did new telescopic evidence decisively disprove Ptolemy’s theory? Kepler’s Theory 15. “Kepler was attracted to Copernicus’s theory because the known data supported that theory.” True or false? Explain. 16. Describe Brahe’s work and its effect on the theories of Copernicus and Ptolemy. 17. What aspect of Kepler’s theory would have horrified all previous astronomers? 18. According to Kepler’s theory, what geometric shape fits the planetary orbits? The Scientific and Copernican Revolutions 19. What is the most characteristic and significant feature of science? 20. Describe several characteristics of a good scientific theory. 21. Can a scientific theory be proved (can we show that the theory is certainly true)? Can it be disproved? Explain. 22. Strictly speaking, Kepler’s theory has been disproved. What has been found wrong with it? Why, then, do we still use it? 23. How does a hypothesis differ from a theory? 24. Distinguish between the Copernican theory and the Copernican revolution. 25. In what sense can evolutionary biology be said to be “Copernican”? conceptual exercises Odd-numbered answers are in the back of the book. Observing the Night Sky 1. How can you tell, from direct observation alone, whether a particular object in the sky is a planet? 2. Draw a diagram showing the positions of Earth, the moon, and the sun at new moon, crescent moon, nearly full moon, and full moon. 3. Are the stars in Figure 1.4 circling clockwise or counterclockwise? A time-lapse photograph made in the Southern Hemisphere, looking toward the South Pole, would also show the stars moving in a circle around a fixed point in the southern sky. Would the stars in the southern view be circling clockwise or counterclockwise? Ancient Greek Theories 4. Describe an unaided-eye observation you could make to disprove the theory that the planets orbit Earth in a simple, uniform, circular motion. 5. Describe an unaided-eye observation you could make to disprove the theory that the planets orbit Earth attached to transparent spheres that rotate in a complicated fashion but that are always centered on Earth. 6. In seeking an explanation of retrograde motion, why didn’t the Greeks just allow the planets to change their speed and direction of motion as the planets moved along circular paths around Earth, instead of resorting to circles within circles? Copernicus’s Theory 7. Is it possible that on some evenings the planet Mars is the evening star? Is this very likely? (See Figure 1.14.) 8. Use Copernicus’s theory to predict whether Mars goes through moonlike phases. Do we ever see a “full Mars”? A “new Mars”? 9. It is possible, but difficult, to see the planet Mercury with the unaided eye. How, then, would you go about finding it? 10. Use Copernicus’s theory (Figure 1.14) to explain why Venus often appears as the morning star or the evening star (compare this with Concept Check 3). Kepler’s Theory 11. Which aspects of Kepler’s theory would Copernicus have liked? Disliked? 12. Would Kepler’s theory have agreed with the data available in Ptolemy’s time? In Copernicus’s time? 13. Did Brahe’s data prove that planets move in ellipses? Explain. 14. Is there anything in Kepler’s theory that resembles the displaced centers of Ptolemy and Copernicus? 15. Who is the “observer” mentioned by Kepler in the quotation on page 19? 16. In the quotation on page 19, Kepler says that God has waited 6000 years. Why 6000? 17. Explain how to get a highly elliptical (elongated) orbit from the tack-and-string construction of Figure 1.20. The Scientific Revolution 18. Because Darwinian evolution is only a theory, we need not take it seriously. Comment? 19. What is the most important and characteristic feature of science? 20. Can two different theories both be true in the sense that at some particular time in history, they correctly predicted the known data? Defend your answer with a historical example. 21. “If Earth is curved, it must have a spherical shape, because a sphere is the most perfect curved solid form.” Does an aesthetic argument like this have any place in science? 22. A sensationalist tabloid “news”paper carries this headline: “SCIENTISTS PREDICT THAT THE UNIVERSE AND EVERYTHING IN IT WILL DOUBLE IN SIZE AT THE BEGINNING OF THE NEXT NEW YEAR!” Is this a testable hypothesis? If so, how could you test it, and if not, why not? Is this good science, bad science, or neither? 23. What is the scientific attitude toward beliefs such as astrology, dianetics, extrasensory perception (ESP), visitations by extraterrestrials, a 6000-year-old Earth, the Bermuda Triangle, and pyramid power? 24. Aristotle, a careful observer of living organisms, wondered where the material that contributes to the growth of a plant comes from. He hypothesized that all of it comes from the soil. Based on your knowledge of biology, do you consider this hypothesis to be correct? Propose an experiment to test this hypothesis. 25. Some people believe that plants will grow better if they talk to them. Is this a testable hypothesis? If so, propose an experiment to test it. 26. “Certain people are gifted with extrasensory perception (ESP), such as the ability to move material objects with their own minds. However, ESP is so delicate that every attempt to verify it always destroys it.” Is this a scientific hypothesis? 27. Isaac Newton predicted that because of its spinning motion, Earth would bulge out near the equator and be flattened near the poles. In 1735 the French Academy of Sciences sent an expedition to the Arctic to measure the exact shape of Earth. When they returned, reporting the predicted results, the philosopher Voltaire mocked them with the following couplet: To distant and dangerous places you roam To discover what Newton knew staying at home. Was Voltaire’s sarcasm justified? Why or why not? 28. Consider the flat Earth hypothesis. Give evidence for this hypothesis. Give evidence against it. The Copernican Revolution 29. Since there are some 100 billion stars in a typical galaxy, and since there are at least 100 billion galaxies in the known parts of the universe, how many stars are there in the known universe? Write this number out. 30. An astronomical unit (AU) is the distance from Earth to the sun. The radius of the approximately circular orbit of Mars is about 1.5 AU. As Earth and Mars orbit the sun, what is their greatest and least distances apart, measured in AU? 31. A light-year (LY) is the distance light travels in one year. Our nearest neighboring star is 4 LY away. Using the fact that light gets here from the sun in 8 minutes, how many AU (preceding problem) is it to our nearest neighboring star? 32. The astronomical object known as the Crab Nebula is the remnant of an exploded star. The explosion was seen, by the Chinese, in a.d. 1054. However, the Crab Nebula is about 3500 LY (preceding problem) distant from Earth. In what Earth year did the star actually explode?