Waves · Quick Reference

Sound Waves Cheat Sheet

Waves · Lesson 2/7

In one line: sound is a longitudinal mechanical wave created by vibrating objects, traveling through air (or other media) as a series of compressions and rarefactions.

Key Ideas

1How Sound is Produced. A vibrating object (like a speaker cone or vocal cords) pushes and pulls on nearby air molecules, creating alternating regions of compression (high pressure) and rarefaction (low pressure).

2Speed of Sound. Sound travels at approximately 343 m/s in air at room temperature; it travels faster through denser media like water or solids.

3Pitch and Loudness. Pitch corresponds to frequency (higher frequency = higher pitch); loudness corresponds to amplitude (larger amplitude = louder sound).

4The Decibel Scale. A logarithmic scale used to measure sound intensity, because the human ear can detect an enormous range of sound intensities.

5Sound Cannot Travel Through a Vacuum. Since sound is a mechanical wave, it requires a medium (like air, water, or a solid) to propagate -- famously, 'in space, no one can hear you scream'.

Worked Examples

A sound wave has frequency 440 Hz (a musical note A) and travels at 343 m/s. Find its wavelength.

Approximately 0.78 meters

Why can astronauts not hear each other speak directly in the vacuum of space?

Sound cannot travel through a vacuum, since it needs a medium to propagate

Why does sound travel faster through steel than through air?

Denser, more rigid media transmit sound vibrations faster than less dense media like air

Formulas

Speed of sound in air (room temp) ≈ 343 m/s

Practice Yourself

A sound wave has frequency 220 Hz, speed 343 m/s. Find wavelength.

343/220≈1.56m

What does a higher frequency sound wave correspond to?

Higher pitch

What does a larger amplitude sound wave correspond to?

Louder sound