![]() So if we know any two of these variables (wavelength, frequency, speed), we can calculate the third. The wavelength (λ), frequency ( f), and speed ( v) of a wave are related by a simple equation: v = fλ. The wavelength is the distance (in space) between corresponding points on a single cycle of a wave (e.g., the distance from one compression maximum (crest) to the next). On average, the frequency range for human hearing is from 20 Hz at the low end to 20,000 Hz at the high end. The higher the frequency, the higher the perceived pitch. For a sound wave, the frequency corresponds to the perception of the pitch of the sound. ![]() The period is simply the reciprocal of the frequency ( T = 1/ f). Graphs of high (top) and low (bottom) frequency waves (Henderson, 2004).įigure 2 also shows the period ( T) of the wave, which is the time that elapses during a single cycle of the wave. The low frequency wave graph on the bottom has only 3 peaks and 3 troughs in the same amount of time.įigure 2. The graph of high frequency waves has a wavelength that has 6 peaks and 6 troughs. The peaks in the graph correspond to the compressions (increase in pressure) and the troughs in the graph correspond to the rarefactions (decrease in pressure). If we were to measure the changes in pressure with a detector, and graph the results, we could see how the pressure changes over time, as shown in the bottom part of Figure 1. The top part of Figure 1, below, represents the compressions (darker areas) and rarefactions (lighter areas) of a pure-tone (i.e., single frequency) sound wave traveling in air (Henderson, 2004). In addition to speed, we will also find it useful to describe waves by their frequency, period, and wavelength. One way to describe a wave is by its speed. At sea level (one atmosphere of pressure) and room temperature (20☌), the speed of sound in air is about 344 m/s. The exact speed depends on the number of air molecules and their intrinsic (existing) motion, which are reflected in the air pressure and temperature. Than the rippling water waves from the stone (you hear the sound long before the ripples reach you). The sound waves from the stone also travel much faster If you could see them, the pattern of sound waves from the stone hitting the water would resemble an expanding hemisphere. Sound waves travel through the air in a similar manner, but in all three dimensions. ![]() When you throw a stone into a still pond, you see a pattern of waves rippling out in circles on the surface of the water, centered about the place where the stone went in. Since the air molecules are already in constant motion, the compressions and rarefactions starting at the original source are rapidly transmitted through the air as an expanding wave. The pushes cause a local compression of the air (increase in pressure), and the pulls cause a local rarefaction of the air (decrease in pressure). The vibrations push and pull on air molecules. Sound is produced by vibrations of objects. What is sound? Sound is a wave, a pattern-simple or complex, depending on the sound-of changing air pressure. We especially recommend exploring the "Sound Waves and Music" articles (Henderson, 2004). The Bibliography section, below, has some good starting points for researching this project. We'll provide a quick introduction here, but for a more complete understanding we recommend some background research on your own. You'll need to understand some basic properties of waves to get the most out of this project. You'll learn how the frequency (perceived as pitch) of the string vibration changes as the effective length of the string is changed by fretting it. In this project, you'll investigate the basic physics of standing waves on guitar strings. ![]()
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