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Welcome to the Greenwood.Net Curiosity Corner

From tthe Textbook

Jul 29, 2021

Curiosity Corner
Dr. Jerry D. Wilson,
Professor Emeritus of Physics
Lander University

As some of you know, I write textbooks. At the end of last year (2020), I finished up a new edition of An Introduction to Physical Science, 15th edition, for Cengage Learning. One of the features of this book has been Conceptual Questions and Answers. Conceptual in nature (no mathematics), questions designed to stimulate students interest in chapter material, and with the answers given.

I thought I’d share some of these with you in the Curiosity Corner, hoping that you’ll find them interesting. Some have probably been in the Curiosity Corner before—after 30 years, I can’t remember. But, review is good! Hope you enjoy.

Question: Here’s an old one. If a tree falls in the forest where there is no one to hear it, is there sound?

Answer: Physically, sound is simply wave disturbances (energy) that propagates in solids, liquids and gases (like air). When perceived by our ears, sound is interpreted as speech, music, noise and so on. The answer to the question depends on the distinction between physical and sensory sound. The answer is no if thinking in terms of sensory hearing (no one there), but yes if considering physical waves. An instrument could be placed in the forest to detect the latter.

Question: When you look into the front side of a shiny spoon, you will see an inverted image of yourself. When looking into the back side of the spoon, your image is upright. Why?

Answer: You are alternately looking at concave and convex mirrors. Looking into the front of the spoon, or a concave mirror, as an object you are outside the focal point and the image is inverted. As you move the spoon away from you, the inverted image becomes smaller. Looking at the back of the spoon, or a convex mirror, your image is upright as all images are for a convex mirror. Get a spoon and try it.

Question: At night, a glass windowpane acts a mirror viewed from the inside a lighted room. Why isn’t it a mirror during the day?

Answer: When light strikes a transparent medium such as glass, some of the light is transmitted and some is reflected. During the day, the light reflected from the inside of the window is overwhelmed by the light coming through the window from the outside and we see images of external objects. At night though, when the light transmitted from the outside is greatly reduced, the inside reflection of the light from the room can be discerned and the windowpane acts as a mirror. (Can you now explain the principle of one-way mirrors and reflective sunglasses?)

C.P.S. (Curious Postscript): “Old wood best to burn, old wine to drink, old friends to trust and old authors to read.” -Francis Bacon

Curious about something? Send your questions to Dr. Jerry D. Wilson, College of Science and Mathematics, Lander University, Greenwood, SC, 29649, or email jerry@curiosity-corner.net. Selected questions will appear in the Curiosity Corner. For Curiosity Corner background, go to www.curiosity-corner.net.

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