17.2 Speed of Sound, Frequency, and Wavelength

Imagine you observe two fireworks explode. You hear the explosion of one as soon as you see it. However, you see the other firework for several milliseconds before you hear the explosion. Explain why this is so.

You observe two musical instruments that you cannot identify. One plays high-pitch sounds and the other plays low-pitch sounds. How could you determine which is which without hearing either of them play?

A teacher wants to demonstrate that the speed of sound is not a constant value. Considering her regular classroom voice as the control, which of the following will increase the speed of sound leaving her mouth?

1. Submerge her mouth underwater and speak at the same volume.
2. Increase the temperature of the room and speak at the same volume.
3. Increase the pitch of her voice and speak at the same volume.
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When poked by a spear, an operatic soprano lets out a 1200-Hz shriek. What is its wavelength if the speed of sound is 345 m/s?

Calculate the speed of sound on a day when a 1500 Hz frequency has a wavelength of 0.221 m.

Show that the speed of sound in $\text{20}.\text{0}º\text{C}$ air is 343 m/s, as claimed in the text.

Dolphins make sounds in air and water. What is the ratio of the wavelength of a sound in air to its wavelength in seawater? Assume air temperature is $\text{20}.\text{0}º\text{C}$.

(a) If a submarine’s sonar can measure echo times with a precision of 0.0100 s, what is the smallest difference in distances it can detect? (Assume that the submarine is in the ocean, not in fresh water.)

(b) Discuss the limits this time resolution imposes on the ability of the sonar system to detect the size and shape of the object creating the echo.

Suppose a bat uses sound echoes to locate its insect prey, 3.00 m away. (See the figure.) (a) Calculate the echo times for temperatures of $\text{5}.\text{00}º\text{C}$ and $\text{35}.\text{0}º\text{C}$. (b) What percent uncertainty does this cause for the bat in locating the insect? (c) Discuss the significance of this uncertainty and whether it could cause difficulties for the bat. (In practice, the bat continues to use sound as it closes in, elimina…