Waves — Light and Sound

Wave your hand up and down — that moves the air in a pattern. Now drop a rock in water — the splash creates ripples that travel across the pond. These are WAVES. Light and sound are both waves too, but you cannot see them directly. Today we crack their secrets.

A WAVE is a disturbance that travels from place to place, carrying energy.\n\n- **Up and down** — like ocean waves\n- **Back and forth** — like sound in air\n- **Ripples** — in water\n\nWaves have:\n- **Amplitude** — how BIG the wave is (loud vs. quiet sound; bright vs. dim light)\n- **Frequency** — how FAST the wave repeats (high vs. low pitch; different colors)\n- **Speed** — how fast the wave travels

Sound is made when something VIBRATES. Speak — your voice box vibrates. The vibration pushes air, which pushes more air, which pushes more... all the way to someone's ear.\n\nSound needs SOMETHING to travel through — usually air, but also water or solid walls. In OUTER SPACE, there is no air — and NO SOUND. That is real.

Light is different — it can travel through EMPTY SPACE. That is how sunlight reaches Earth across 93 million miles of nothing.\n\nLight is made of tiny packets called PHOTONS. Different colors of light are different FREQUENCIES — red has a lower frequency; violet has higher.\n\nSpeed of light: 186,000 miles per second. Fastest thing in the universe.

| Feature | Light | Sound |\n|---|---|---|\n| Speed | 186,000 mi/sec | ~770 mph |\n| Needs medium? | No — travels in space | YES — air, water, solid |\n| Travels in waves | Yes | Yes |\n| We detect with | Eyes | Ears |\n\nDifferent, but both carry energy.

- **Radio waves** (a kind of light) — send music to your car\n- **Microwaves** — heat your food\n- **Visible light** — let us see\n- **X-rays** — show bones\n- **Sound waves** — speech, music, dolphins' echolocation\n- **Ultrasound** — lets doctors see inside bodies\n\nAll of it is waves.