Solutions Manual Conceptual Physics 13th Edition By Hewitt All Chapters,

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1 About Science ____________________________________________ Conceptual Physics Instructor’s Manual, 13e, 1.1 Scientific Measurements How Eratosthenes Measured the Size of Earth PRACTICING PHYSICS Earth’s Size via Tree/Flagpole Shadows Size of the Moon Distance to the Moon Distance to the Sun Size of the Sun Mathematics—The Language of Science 1.2 Scientific Methods The Scientific Attitude Dealing with Misconceptions 1.3 Science, Art, and Religion FAKE SCIENCE 1.4 Science and Technology RISK ASSESSMENT 1.5 Physics—The Basic Science 1.6 In Perspective

OPENING PHOTOS AND PROFILE All chapters open with photos of educators. Chapter 1 opens with a photo of my wife, Lil, pointing to many circular images of the Sun beneath a tree in front of our residence in St. Petersburg, Florida. The second photo is of my young protégé Einstein Dhayal from India (right) with his friends telling time with solar shadows. The third photo is of my friend and science writer Judith Brand who assisted in the writing of this edition. She shows how lining up a pea with the Moon leads to estimating its distance from Earth.

The last photo is of the Vasquez family, all teachers, that begin with Phyllis Vasquez, colleague at City College of San Francisco (CCSF), and her sons in order of age from oldest to youngest: Michael, David, Rodney, John, and Robert, who all took my class. The question suggested by the photo is how many Moons away from Earth is the Moon? This leads to a very nice Moon-Earth activity.

The profile is of Greek mathematician Eratosthenes.

INTRODUCTION Like many introductions, much of this introductory chapter can be regarded as a personal essay. In my teaching days I didn’t discuss Chapter 1. Today I would, due to the high interest in Eratosthenes and his intriguing way of measuring Earth’s circumference in about 235 BC. And I would certainly present what I see as a great feature of this edition, the easy-to-do green-pea activity of judging the Moon’s distance from Earth, as Judith Brand illustrates.

SUPPLEMENTS Practicing Physics (Available on MasteringPhysics for Hewitt Conceptual Physics.)

• Measuring the Size of Planet Earth • The Moon, Sun, and a Green Pea • Flagpole Physics • Solar Images • Making Hypotheses Next-Time Questions (Available on MasteringPhysics for Hewitt Conceptual Physics.)

• Scientific Claims • Pinhole Image of the Sun • With Simply a Pair of Sticks • Solar Image • Flagpole Shadows • Just a Pair of Sticks © 2023 Pearson Education Limited. All Rights Reserved.

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• Cone, Ball, and a Cup

• Eratosthenes Sticks

• Two Sticks and a Shadow

Hewitt-Drew-It! Screencast (Available at www.HewittDrewIt.com.)

• Eratosthenes (no. 148) Laboratory Manual (Available separately for purchase.)

There are no labs for this chapter.

SUGGESTED PRESENTATION Eratosthenes, Aristarchus, and Sun-Moon Measurements Measurements are a hallmark of science. What more intriguing ones than the sizes and distances of our Sun and Moon. I suggest beginning your course with the measurements of Eratosthenes for Earth, followed by Aristarchus and his measurements of the Moon. Whenever a half moon is viewed in the sky, our line of sight to the Moon and its line of sight to the Sun define the imaginary right triangle in the sky envisioned by Aristarchus (Figure 1.8), which is worthy of intriguing class discussion.

Begin by asking your students to come up with two ways to determine the circumference of a pizza pie if they had only one slice. Then progress to the following demonstration.

DEMONSTRATION: I’m excited about a new activity in this edition (Flagpole Physics in Practicing Physics) inspired by the first calculation of Earth’s size by Eratosthenes. And that’s to do the reverse: using Earth’s circumference to calculate the distance between far-apart locations—such as far-apart school flagpoles.

You can use the second part of the activity, A Model Orange, as a demo. Hold an orange before your students. The orange nicely approximates a sphere. Poke two long toothpicks perpendicular to the surface of the spherical fruit and ask where they’ll meet inside.

They’ll intersect at the center of the sphere. Whatever the angle is between the toothpicks, that’s the vertex angle they make with the center of the sphere. The arc between the two sticks makes up a segment of a circle. How many such segments make up a full 360°?

That number, multiplied by the distance between the toothpicks at the surface tells you the circumference of the sphere. If the vertex of the segment is, say, 36°, then ten segments form the circumference.

Apply this to flagpoles that are very far apart—extreme social distancing. Rather than calculating Earth’s circumference, use its known value of 40,000 km and calculate the distance between school flagpoles. (The first part of the Flagpole Physics activity.) The Next-Time Question Flagpole Shadows also goes well with this material. It’s reproduced following this Suggested Presentation.

Measuring Solar Diameter One of my very favorite class assignments is the task of measuring the diameter of the Sun with a ruler or tape measure. This makes sense by first explaining the physics of a pinhole camera. The pinhole image technique is described in Solar Images in Practicing Physics and in Figure 1.9. Hold a meterstick up and tell the class that with a measuring

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device, such as a strip of measuring tape or a simple ruler, they can measure the diameter of the Sun. Call attention to Figure 1.9, then sketch and explain the simple pinhole camera thusly. (More pinhole information is in Chapter 28.)

Tell of how a small hole poked in a piece of cardboard will show the image of the Sun when the card is placed in sunlight. You can explain this without referring to Figure 1.9 in the textbook because the figure gives the ratio you wish them to determine. I find this early assignment very successful, in that simple measurements yield a most impressive value—a confidence builder. For those who don’t succeed, or succeed partially, I urge them to try again for full credit.

Pinhole Images of the Sun I can’t overestimate the value of spending time on the pinhole image idea. If you’re near a sunlit window you can show how a tiny hole in a piece of card projects an image of the Sun. Most intriguing is doing this with different shaped holes. A small triangle in a piece of card will show not a triangle, but the circular shape of the Sun. The shape of the hole is irrelevant. It just has to be small compared with the distance of the card from the floor. All students find this intriguing. Especially when you tell them of the solar images beneath sunlit trees. They will forever look at the circular spots of light beneath sunlit trees in a different way. And they will be reminded of your lesson. (A question to their friends: When was the first time you noticed that spots of light beneath sunlit trees are pinhole images of the Sun?) That 110 Suns can fit in the space between Earth and the Sun should be intriguing to students.

Additionally, 110 Moons can fit in the space between Earth and the Moon! Discussion of the pea held at arm’s length to eclipse the Moon holds high interest. (See The Moon, Sun, and a Green Pea in Practicing Physics.)

Scientific Thinking Consider elaborating on the idea about the possible wrongness versus rightness of ideas; an idea that characterizes science. A test for being wrong is not well understood. Expand on the idea that honesty in science is not only a matter of public interest, but is a matter of self-interest. Ideally, there are no second chances for a scientist who’s found to be dishonest. The high standards for acceptable performance in science, unfortunately, do not extend to other fields that are as important to the human condition. For example, consider the standards of performance required of politicians.

Distinguish among Hypothesis, Theory, Fact, and Concept Point out that theory and hypothesis are not the same. A hypothesis (an educated guess) proposes an explanation for something observed; it must be testable. A theory applies to a synthesis of a large body of information. The criterion of a theory is not whether it is true or untrue, but rather whether it is useful or not. A theory is useful even though the ultimate causes of the phenomena it encompasses are unknown.

For example, we accept the theory of the big bang as the beginning of the observable universe. The theory can be refined, or with new information it can take on a new direction or develop new insights and contribute to the advancing of knowledge. It is important to acknowledge the common misunderstanding of what a scientific theory is, as revealed by those who say, “But it is not a fact; it is only a theory.” Many people have the mistaken notion that a theory is tentative or speculative, while a fact is absolute.

Impress upon your class that a fact is not immutable and absolute, but is generally a close agreement by competent observers of a series of observations of the same phenomena. The observations must be testable. Since the activity of science is the determination of the most probable, there are no absolutes.

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Facts that were held to be absolute in the past are seen altogether differently in the light of present-day knowledge.

By concept, we mean the intellectual framework that is part of a theory. We speak of the concept of time, the concept of energy, or the concept of a force field. Time is related to motion in space and is the substance of the special theory of relativity. We find that energy exists in tiny grains, or quanta, which is a central concept in the quantum theory. A concept envelops the overriding idea that connects various phenomena. Thus, when we think “conceptually” we envelop a generalized way of looking at things.

Dealing with Misconceptions The notion of a self-test for determining whether one’s thinking is on a right or wrong track goes back to many rap sessions with fellow students in my college days. I incorporated the outcome of those insightful chats in the first edition of Conceptual Physics, which I’ve repeated in all editions thereafter. I hope this material elicits spirited discussions among your students today.

Prediction Prediction in science is different than prediction in other areas. In the everyday sense, one speaks of predicting what has not yet occurred, like whether or not it will rain next weekend. In science, however, prediction is not so much about what will happen, but about what is happening and is not yet noticed, like what the properties of a hypothetical particle are and are not. A scientist predicts what can and cannot happen, rather than what will or will not happen.

In biology, for example, you explain events once you see them. In a sense you’re looking at the historical behavior and then you explain patterns. In physics you’re more likely to predict patterns before they’re seen.

Science and Technology In discussions of science and technology and their side effects, a useful statement is that you can never do just one thing. Doing this affects that. Or, You can never change only one thing. Every time you show an equation, it’s evident that changing a variable on one side of the equation changes one or more on the other side. This idea is nicely extended with there is never just one force in discussions of Newton’s third law.

Science, Art, and Religion Einstein said, “Science without religion is deaf; religion without science is blind.” The topic of religion in a science textbook is rare. I treat it briefly only to address what is foremost on many students’ minds. Do religion and science contradict each other? Must one choose between them? I hope my very brief treatment presents a satisfactory answer to these questions. My take is that religion and science are compatible when they address their respected realms. Your students need no new examples of the horror that results when extremist thinking dominates. Disputes in science are settled by experiment and better evidence. No wars are fought over science! Your feedback on my inclusion of science/religion in this book will be appreciated.

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