What Is a Wave?
A wave is a disturbance that carries energy without carrying matter. When you drop a stone in water, ripples spread outward — the water itself doesn't travel across the pond, only the pattern travels.
Transverse vs Longitudinal
In transverse waves (light, water ripples), the disturbance is perpendicular to the direction of travel. In longitudinal waves (sound), the disturbance is parallel — like a slinky spring you push and pull. Sound waves are compressions and rarefactions of air molecules.
Frequency and Pitch
Frequency (waves per second, measured in hertz) determines pitch. A 440 Hz sound wave sounds like the note A above middle C. Double the frequency (880 Hz) sounds one octave higher. The human ear can hear 20 Hz to 20,000 Hz.
The Doppler Effect
When a siren approaches, its sound waves bunch up in front of you, making a higher pitch. As it passes and moves away, the waves stretch out, making a lower pitch. This is the Doppler effect — and it's how radar guns measure car speeds.
Wave Applications
From ultrasound imaging to radio communication to oceanography, waves are everywhere in technology. Understanding wave physics lets doctors see babies in the womb and lets your phone receive data from satellites thousands of kilometers away.