Lesson 3: Waves — How the Universe Sends Messages
Waves — How the Universe Sends Messages
Almost everything you experience arrives as a wave. Sound. Light. Heat. Wi-Fi. Earthquakes. Understanding waves means understanding how the universe communicates.
What Is a Wave?
A wave is a disturbance that transfers energy from one place to another without transferring matter. When you drop a rock in a pond, the water doesn't travel to the shore — the energy does, in the form of ripples.
Two Types of Waves
Transverse waves — the disturbance moves perpendicular to the wave direction. Think of a rope you shake up and down while the wave travels forward. Light is a transverse wave.
Longitudinal waves — the disturbance moves parallel to the wave direction. Sound is a longitudinal wave. Air molecules get compressed and stretched in the same direction the sound is traveling.
Key Wave Properties
Wavelength — the distance between two peaks. Short wavelength = high frequency = high energy.
Frequency — how many waves pass a point per second. Measured in Hertz (Hz). Middle C on a piano is 262 Hz — 262 waves hit your eardrum every second.
Amplitude — the height of the wave. Higher amplitude = louder sound or brighter light.
Speed — speed = wavelength × frequency. Sound travels at about 343 m/s in air. Light travels at 300,000,000 m/s — roughly a million times faster.
The Doppler Effect
Ever notice how an ambulance siren sounds higher pitched as it approaches and lower as it drives away? That's the Doppler effect. As the ambulance moves toward you, sound waves get compressed — higher frequency, higher pitch. As it moves away, they stretch out — lower frequency, lower pitch.
Astronomers use this with light to measure how fast galaxies are moving. Light from galaxies moving away from us is "red-shifted" — stretched toward the red (lower frequency) end of the spectrum. This is how we know the universe is expanding.
Why Is the Sky Blue?
Sunlight contains all colors (wavelengths). When it enters Earth's atmosphere, it collides with gas molecules. Short wavelengths (blue) scatter much more than long wavelengths (red). So blue light bounces all over the sky in every direction — the whole sky glows blue. At sunset, light travels through more atmosphere to reach you, so most blue is scattered away and only red/orange makes it through.
Think About It
- Why can you hear bass from a car stereo through walls but not treble?
- Why do doctors use ultrasound instead of regular sound to image babies?
- Submarines use sonar. What type of wave is that and how does it work?