Sound Wave
A game of dominoes where air particles bump their neighbors to pass energy forward.
Definition A wave created when vibrations from voices or instruments push and pull through surrounding matter like air or water. Our ears hear diverse sounds by sensing these tiny ripples of air pressure.
Vibrations Passing Like Dominoes
When you hit a drum, the tight drumhead vibrates back and forth rapidly. This vibration shoves the air particles right next to it. Those bumped particles tap the ones beside them and bounce back to where they started.
Air particles do not fly all the way from a speaker's mouth to a listener's ear. Just like a line of people tapping each other on the shoulder to pass a message, only the vibrational energy moves forward while the particles stay in place.
As this happens, alternating patches of squished-together and spaced-out air particles spread in every direction. Because the particles oscillate back and forth parallel to the wave's path, scientists call this a 'longitudinal wave.'
Ocean waves are transverse waves that bob up and down while moving forward. Sound, on the other hand, is a wave of pressure that repeatedly squeezes and stretches the air.
To Be More Precise
To be more precise, sound waves require a mediumโa stepping-stone substanceโto carry vibrations along. In outer space or inside a vacuum jar where there are no air or water molecules, even a massive explosion makes no sound at all.
Sound travels at vastly different speeds depending on the medium. In air, where particles are loosely scattered, sound travels at about 340 meters (1,115 feet) per second. But in water, where particles are packed more closely, it zooms along at roughly 1,500 meters (4,920 feet) per second.
In solids like steel pipes or railroad tracks, sound races at over 5,000 meters (16,400 feet) per second. The tighter and denser the particles are packed, the faster they pass vibrations to their neighbors.
You might remember scenes from classic Western movies where a character puts an ear to the train tracks to hear a distant train coming. That was clever science in actionโcatching the fast vibrations traveling through solid steel long before the horn's sound arrived through the air.
The Secret to Pitch and Volume
Why does a mosquito buzz with a sharp, high whine while a big bass drum rumbles low and deep? The secret lies in frequency, which measures how many times air particles vibrate per second. The faster the air vibrates in a second, the higher the pitch; the slower it vibrates, the lower and deeper the note.
Human ears can usually only hear sounds vibrating between 20 and 20,000 times per second. Vibrations beyond 20,000 times per second are called 'ultrasound.' Bats and dolphins beam ultrasound through the air or water and listen to the returning echoes to navigate and hunt.
Sound volume, meanwhile, depends on how forcefully and widely the air particles swing. A larger wave amplitude strikes our eardrums harder, which our brain interprets as a louder sound.
A gentle whisper makes air particles flutter softly in place. But when you shout, air particles swing wildly with large amplitude, launching powerful energy into the surrounding air.
๐ค Common misconceptions
We hear sound because air particles fly directly from the speaker's mouth into our ears.
Air particles merely vibrate back and forth in place. What actually travels forward is the vibrational energy, not the particles themselves.
๐งบ Where you meet it
A sound wave is a wave where particles vibrate in place to pass energy along to their neighbors.