PART IV Oscillations and Waves
OVERVIEW
The Wave Model
Parts I–III of this text have been primarily about the physics of particles. You’ve seen that systems ranging from balls and rockets to planets can be thought of as particles or as systems of particles. A particle is one of the two fundamental models of classical physics. The other, to which we now turn our attention, is a wave.
The song of a humpback whale can travel hundreds of kilometers underwater. This graph uses a procedure called wavelet analysis to study the frequency structure of a humpback whale song.
Waves are ubiquitous in nature. Familiar examples include
Undulating ripples on a pond.
The swaying ground of an earthquake.
A vibrating guitar string.
The sweet sound of a flute.
The colors of the rainbow.
The physics of oscillations and waves is the subject of Part IV. The most basic oscillation, called simple harmonic motion, is still the motion of a particle. But oscillators are the sources of waves, and the mathematical description of oscillation will carry over to the mathematical description of waves.
A wave, in contrast with a particle, is diffuse, spread out, not to be found at a single point in space. We will start with waves traveling outward through some medium, like the spreading ripples after a pebble hits a pool of water. These are called traveling waves. An investigation of what happens when waves travel through each other will lead us to standing waves, which are essential for understanding phenomena ranging from those as common as musical instruments to as complex as lasers and the electrons in atoms. We’ll also study one of the most important defining characteristics of waves—their ability to exhibit interference.
Our exploration of wave phenomena will call upon sound waves, light waves, and vibrating strings for examples, but our goal will be to emphasize the unity and coherence that are common to all types of waves. Later, in Part VII, we will devote three chapters to light and optics, perhaps the most important application of waves. Although light is an electromagnetic wave, your understanding of those chapters will depend on nothing more than the “waviness” of light. If you wish, you can proceed to those chapters immediately after finishing Part IV. The electromagnetic aspects of light waves will be taken up in Chapter 31.