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# 8.1: Introduction to Waves

• Contributed by Wendell Potter and David Webb et al.
• Physics at UC Davis

We begin our study of waves in this first unit of Physics 7C with an introduction to waves and then a thorough development of the harmonic plane wave model, which we will use extensively to model and understand a wide variety of wave phenomena.

In this section we will familiarize ourselves with waves by concentrating on material waves. These are the disturbances of atoms or molecules of a particular substance. Any sort of ripple that you have seen is a material wave; sound is a material wave. There are other types of waves such as light or matter waves which are not as easy to visualize, and we shall postpone detailed discussion of these waves until later.

One of the distinguishing features of physics is that physicists continually strive for general principles and simple models that can be applied to large classes of phenomena. In our study of wave phenomena we consciously take this approach. The focus is on the models and their representations, not on any one of an almost unlimited number of individual examples associated with waves (like sound, light, TV and radio waves, microwaves, etc.) Our goal is to enable you to develop a useful understanding of wave behavior that you can apply to any phenomenon that can be modeled as a wave.

• 1. What is a Wave?
There are two important goals associated with the first part of this unit. Firstly, to become familiar with wave phenomena and how we analyze them, and secondly, to sufficiently understand the mathematical representation of one-dimensional harmonic waves. We want to use this mathematical representation as a tool throughout the rest of the course to help us understand the physics of sound and light waves.
• 2. Wave Properties and Characteristics
In most material waves we typically encounter, the "shape" of the disturbance stays the same over short travel distances. In our example of a rock thrown into a pond, the ripples look similar as they expand away from the initial disturbance. Over greater distances, however, we notice changes. The ripples seem to die out as the radius of the circle they make increases This is because as the wave spreads out, its energy disperses.
• 3. Harmonic Waves
Mechanical harmonic waves can be expressed mathematically as sinusoidal.
• 4. Graphical Representations of Waves
• 5. Other Types of Waves
• 6. Summary