The Science of Sound
Sound is a huge part of our daily experience, from the music we listen to, to the conversations we have. But what is sound, scientifically?
Sound is a Wave
Sound is a form of energy that travels as a wave. Specifically, sound is a:
Mechanical Wave: This means it needs a medium (a substance) to travel through. It can travel through solids, liquids, and gases, but it cannot travel through a vacuum. There is no sound in empty space.
Longitudinal Wave: This means the vibrations of the wave are parallel to the direction of travel. A sound wave is a traveling series of compressions (where air particles are bunched together) and rarefactions (where air particles are spread apart).
How is Sound Produced?
All sounds are created by vibrations.
When you speak, your vocal cords vibrate.
When you strike a drum, the drumhead vibrates.
When you pluck a guitar string, the string vibrates.
These vibrations push and pull on the particles of the surrounding medium (usually air), creating the compressions and rarefactions that travel to our ears as a sound wave. Your eardrum then vibrates in response, and your brain interprets these vibrations as sound.
Properties of Sound: Pitch and Loudness
We can describe a sound wave using the same properties as any other wave, but we perceive them in a special way.
Frequency → Pitch: The frequency of a sound wave determines its pitch. Pitch is how high or low a sound seems.
A high frequency (many vibrations per second) produces a high-pitched sound (like a whistle).
A low frequency (few vibrations per second) produces a low-pitched sound (like a tuba).
Amplitude → Loudness: The amplitude of a sound wave determines its loudness or volume.
A high amplitude wave carries a lot of energy and sounds loud. This corresponds to dense compressions.
A low amplitude wave carries little energy and sounds soft.
The Speed of Sound
The speed of sound is not constant. It depends on the medium it is traveling through. Specifically, it depends on the temperature, stiffness, and density of the medium.
Solids > Liquids > Gases: Sound travels fastest through solids, slower through liquids, and slowest through gases.
Why? The particles in a solid are packed much more tightly together than in a liquid or gas. This allows the vibrations to be passed from particle to particle much more quickly.
For example, the speed of sound in air is about 343 m/s, but in steel, it's about 5,960 m/s!