Textbook Material to Read

Chapter 17 Introduction

17.1 Sound

17.2 Speed of Sound, Frequency, and Wavelength

17.3 Sound Intensity and Sound Level

17.6 Hearing

17.7 Ultrasound

Sound

• Sound is a disturbance of matter that is transmitted from its source outward.
• Sound is one type of wave.
• Hearing is the perception of sound.
• Speed of sound depends on temperature.

Speed of sounds is affected by temperature in a given medium:

[latex]v=(331m/s)\sqrt[2]{\frac{T}{273K}}[/latex],

[latex]T[/latex] is temperature in SI units K (Kelvin).

Wave equation: speed, frequency, and wavelength relationship

speed = frequency x wavelength

[latex]v=f*w[/latex]

frequency = speed / wavelength

[latex]f=v/w[/latex]

wavelength = speed / frequency

[latex]w=v/f[/latex]

This wave equation is true for all types of waves.

Hearing

• The range of audible frequencies is 20 to 20,000 Hz.
• Those sounds above 20,000 Hz are ultrasound, whereas those below 20 Hz are infrasound.
• The perception of frequency is pitch.
• The perception of intensity is loudness.
• Loudness has units of phons.

Ultrasound

Any sound with a frequency above 20,000 Hz (or 20 kHz)—that is, above the highest audible frequency—is defined to be ultrasound.

Ultrasound also has a wavelength that limits the fineness of detail it can detect.

We can never observe details significantly smaller than the wavelength of our probe; for example, we will never see individual atoms with visible light, because the atoms are so small compared with the wavelength of light.

Additional Resources

1. OpenStax High School Physics, chapter 14 Sound

2. Learn with Khan Academy:

Introduction to Sound.

Sound.