Everyday Physics

The following sections are included:

• Dedication
• Preface
• Contents

We start by looking at various kinds of waves that we see around us in daily life. They include the wave of the hand, waves on water surfaces, waves on strings (especially in musical instruments), and waves on flags. Other kinds of waves are largely invisible, such as sound waves, waves on drumheads, earthquakes, light, quantum waves and more. This overview of waves will give us a useful impression of what a wave is like, and also how widespread and important waves are in our daily experience. In particular, resonances in waves are fundamental to speaking and making music.

We start our exploration of waves with a type of wave that we can easily make and observe at home: waves on strings. They are also fundamental to making music with string instruments (guitars, violins, pianos), in particular in the form of resonances and so-called standing waves. We will see how such waves are generated and how they move along strings (or ropes, or toys like slinkies). Very important is the behavior when waves are reflected from the ends of a string…

We first show in this chapter that sound in air (and other gases) is made of waves, and that these waves are density and pressure waves. This is not obvious since waves in air are not visible. We discuss how such waves are created and heard. We find that such waves have much in common with waves on strings, especially if we consider sound in tubes as used in musical wind instruments: superposition and interference, standing waves, resonances, etc. also apply to waves in air…

This chapter focuses on vibrating objects that are two-dimensional. To better understand the case of 2D plates (such as cymbals and metallic drums), we first consider 1D flexible sticks, such as poles, trees, musical triangles and tuning forks. Although waves on sticks operate differently from strings, they also exhibit wave behavior, including interference, reflection at the ends, and standing waves (resonances). As with air in boxes compared to tubes, we find that waves on plates, drums and flags also behave very similarly to waves on strings.

This chapter will link standing waves to the notes that a musical instrument makes. Starting with a simplified model of a piano, we will discuss how string vibrations correspond to notes, pitches and frequencies, and how they are controlled to deliver music. We will also address what distinguishes the sound of different musical instruments, as well as the recording and playback of sounds. We will consider synthetic sounds as well…

We probably use our voice more than any other method to communicate our thoughts to other people. It is fascinating to realize that our mouth makes all sorts of hisses, pops, groans and vibrations to express simple and abstract ideas. And let’s not forget the pleasure of singing and whistling!

In this chapter, we explore how we go from those hisses, pops, groans and vibrations to words. Some of the very interesting questions we will discuss are: How do the sounds that we make become the letters and syllables of words? How different are the voices of males, females and children? How different are the accents, dialects (“varieties”) and languages that humans use? And how are these connected with the sounds that our mouths make? How different is singing from speaking? What are whistling, yodeling, whispering and humming? How can voices be synthesized? How different are animal sounds from human voices?…

Part A of this book, in Chapters 1–7, covered waves “from Musical Instruments and Sounds to Human and Animal Voices”. We first briefly introduced a wide variety of waves, such as waves on strings and in air, waves in and on water, earthquake waves, as well as electromagnetic, gravitational and quantum waves. While these waves can have very different mechanisms, it is found that the behavior of waves is universal: waves typically have smooth shapes that can repeat in space and in time; waves can travel far through substances or space, with characteristic wavelengths, speeds and frequencies; also, waves can cross each other by superposition and cause constructive or destructive interferences…

Part B of this book continues exploring diverse types of important waves with interesting behaviors, from earthquakes and tsunamis to light and the quantum world, as well as beyond to brain waves and human waves. We first extend sound waves from traveling through air (which in Part A was the basis of music and voices) to traveling through liquids and solids: this includes underwater sounds (such as ultrasound) as well as earthquakes, all discussed in Chapter 9…

Sound is ubiquitous in daily life. It is most familiar as waves that travel through air. In this chapter, we follow sound waves that instead travel through liquids and solids, especially through water and rocks. We will compare such sound to sound in air and discuss how similar and/ or different they are. For example, sound waves in liquids and solids travel much faster than in air: we will relate this feature to the atomic and molecular structures of liquids and solids. A special type of wave, called a shear wave, can travel only through solids. Earthquakes cause energetic sound waves that can travel deep through the Earth and far across continents: most of these waves have low frequencies, so they may seem silent to many of us, while being very destructive…

Waves can be reflected, transmitted and refracted (“bent”) when they reach the boundary between different substances. Such universal behavior of waves is particularly important in waves on the surface of water (further discussed in Chapter 11), as well as light waves (see Chapter 12). Common examples are string waves of a musical instrument when they bounce from the end of a string; sound waves in air or liquids or solids when they enter another substance like a wall or a warmer or colder layer of air; surface waves on water approaching a beach; and light waves when they enter and exit water or glass…

Waves on water are the most visible of all kinds of waves. They, as well as waves on other liquids, exhibit most vividly the behavior of waves on strings, sounds in air, liquids and solids, and electromagnetic waves (including light).

However, waves on liquids have very different mechanisms: gravity and surface tension. Also, waves on water often have relatively large amplitudes, so their behavior becomes more complex. Waves with short wavelengths are dominated by surface tension. Waves with longer wavelengths are dominated by gravity; these include such diverse cases as waves at beaches, tides, tidal waves, rogue waves, tsunamis and ships’ wakes…

In this chapter, we focus on light waves and other electromagnetic waves (EM waves such as x-rays and radio waves). The physical principles of EM waves are quite different from those of string waves, sound waves, and waves on water. Nevertheless, EM waves behave in many ways very much like those waves (as well as other waves, which we will discuss in later chapters). For example, we have learned earlier about wave interference, reflection, refraction and diffraction: we will be able to fruitfully apply these concepts to EM waves, and to light in particular…

Quantum mechanical waves (QM waves), sometimes called quantum waves or matter waves, are part of the “modern physics” that was developed in the early 20th century. They gave rise to a revolutionary change in our worldview of nature and to whole new areas of science and technology in wide use today, from electronics to genetics…

Gravitational waves were first detected only recently, in 2015. They had been predicted a century earlier, by Einstein, as part of his theory of general relativity. He was, however, very skeptical that they would ever be seen and initially even thought that they did not exist. This chapter sketches the history and properties of these fascinating waves.

Caution: gravitational waves should not be confused with gravity waves on the surface of water (or other liquids). Although they have the same source (gravity, which is the attraction between masses or objects), they operate on completely different scales of distance, time and speed.

We have seen a wide variety of waves in this book. But there are still many more, so we will briefly introduce other kinds of waves in this chapter! We will also look at the human side of science, to give a feeling for what it is like to do science as a human being.

The waves which we have discussed so far have very different mechanisms, but they also have very strong similarities, mainly their universal “wavy behavior”. In this chapter, we will emphasize such differences and similarities. This will also help us characterize more precisely what is meant by “wavy behavior”…

The following sections are included:

• References and Resources
• Index
• About the Author