Category: Waves—II

If a source is moving toward a stationary detector at a speed equal to the speed of sound—that is, if νS = ν—Eqs. 17-47 and 17-55 predict that the detected frequency f′ will be infinitely great. This means that the source is moving so fast that it keeps pace with its own spherical wavefronts, as Fig. 17-23a suggests. What happens when the speed of…

A police car is parked by the side of the highway, sounding its 1000 Hz siren. If you are also parked by the highway, you will hear that same frequency. However, if there is relative motion between you and the police car, either toward or away from each other, you will hear a different frequency.…

If we listen, a few minutes apart, to two sounds whose frequencies are, say, 552 and 564 Hz, most of us cannot tell one from the other. However, if the sounds reach our ears simultaneously, what we hear is a sound whose frequency is 558 Hz, the average of the two combining frequencies. We also hear a…

Musical sounds can be set up by oscillating strings (guitar, piano, violin), membranes (kettledrum, snare drum), air columns (flute, oboe, pipe organ, and the horns of Fig. 17-13), wooden blocks or steel bars (marimba, xylophone), and many other oscillating bodies. Most instruments involve more than a single oscillating part. In the violin, for example, both the…

If you have ever tried to sleep while someone played loud music nearby, you are well aware that there is more to sound than frequency, wavelength, and speed. There is also intensity. The intensity I of a sound wave at a surface is the average rate per unit area at which energy is transferred by the wave through…

Like transverse waves, sound waves can undergo interference. Let us consider, in particular, the interference between two identical sound waves traveling in the same direction. Figure 17-8 shows how we can set up such a situation: Two point sources S1 and S2 emit sound waves that are in phase and of identical wavelength λ. Thus, the sources themselves are said to…

Here we examine the displacements and pressure variations associated with a sinusoidal sound wave traveling through air. Figure 17-5a displays such a wave traveling rightward through a long air-filled tube. Recall from Lesson 16 that we can produce such a wave by sinusoidally moving a piston at the left end of the tube (as in Fig. 16-2). The piston’s rightward…

The speed of any mechanical wave, transverse or longitudinal, depends on both an inertial property of the medium (to store kinetic energy) and an elastic property of the medium (to store potential energy). Thus, we can generalize Eq. 16-26, which gives the speed of a transverse wave along a stretched string, by writing where (for transverse…

As we saw in Lesson 16, mechanical waves are waves that require a material medium to exist. There are two types of mechanical waves: Transverse waves involve oscillations perpendicular to the direction in which the wave travels; longitudinal waves involve oscillations parallel to the direction of wave travel. In this app, a sound wave is defined roughly as any longitudinal wave. Seismic…

How, then, does a penguin find its mate among the huddled thousands? The answer is in this lesson. After diving into the water and eating, an emperor penguin must crawl back onto its home ice flow and return to its mate. In the winter, however, that mate can be anywhere among thousands of penguins huddled…