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Sound is a form of mechanical energy that travels through matter as a longitudinal wave. In air, vibrating objects create regions of compression and rarefaction that move outward and carry energy to a listener. Hearing matters because it lets humans communicate, detect danger, enjoy music, and gather information about the environment. Physics explains both how sound moves through a medium and how the ear converts that motion into signals the brain can understand.
When sound enters the outer ear, it is funneled down the ear canal to the eardrum, which begins to vibrate. The three tiny ossicles amplify these vibrations and transmit them into the fluid-filled cochlea of the inner ear. Inside the cochlea, specialized hair cells bend in response to fluid motion and convert mechanical vibrations into electrical nerve impulses. The auditory nerve carries these signals to the brain, where they are interpreted as pitch, loudness, and timbre.
Key Facts
- Sound in air is a longitudinal wave made of compressions and rarefactions.
- Wave speed relation: v = fλ, where v is speed, f is frequency, and λ is wavelength.
- Typical speed of sound in air at room temperature is about 343 m/s.
- Frequency determines pitch and is measured in hertz (Hz).
- Amplitude is related to loudness, and greater amplitude means more energy in the wave.
- The ear pathway is outer ear -> ear canal -> eardrum -> ossicles -> cochlea -> auditory nerve -> brain.
Vocabulary
- Longitudinal wave
- A wave in which the particles of the medium vibrate parallel to the direction the wave travels.
- Frequency
- The number of wave cycles passing a point each second, measured in hertz.
- Amplitude
- The maximum displacement of a vibration, which is related to the loudness of a sound.
- Cochlea
- A spiral-shaped inner ear structure filled with fluid that helps convert vibrations into nerve signals.
- Ossicles
- The three tiny middle ear bones that transmit and amplify vibrations from the eardrum to the inner ear.
Common Mistakes to Avoid
- Thinking sound can travel through empty space, which is wrong because sound needs a material medium such as air, water, or solids to carry the vibration.
- Confusing amplitude with frequency, which is wrong because amplitude mainly affects loudness while frequency determines pitch.
- Assuming the ear hears directly with the eardrum alone, which is wrong because the cochlea and hair cells are the structures that convert vibrations into nerve impulses.
- Using v = f/λ, which is wrong because the correct wave relationship is v = fλ, so dividing by wavelength gives the wrong units and value.
Practice Questions
- 1 A sound wave in air has frequency 680 Hz and wavelength 0.50 m. What is its speed?
- 2 A tuning fork produces a sound with frequency 256 Hz. If the speed of sound is 343 m/s, what is the wavelength?
- 3 A high note and a low note are played at the same loudness. Explain which property of the wave changes and how the ear helps the brain detect the difference.