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Sound starts at something shaking. This chapter shows how sound gets to you.

Shake, medium, wave — the whole chapter in one line.

This is Chapter 10, Exploration — Sound Waves: Characteristics and Applications.

What you will learn

Something has to shake. Stop the shaking and the sound stops.
A medium carries it. A medium is what sound travels through. With no medium, no sound arrives.
What moves. The wave travels. The medium only shakes in place.
Loudness. A bigger amplitude is a louder sound. Amplitude is how far a shake moves from rest.
Pitch. More shakes a second is a higher note. Pitch is how high or low a sound seems.
What we hear. People hear 20 Hz to 20 000 Hz. Lower is infrasound. Higher is ultrasound.
Echoes. A hard surface sends sound back.
Sonar. Timing an echo gives a distance.
Wavelength. Speed = wavelength × frequency. Frequency means shakes a second. A wavelength is the length of one wave.

These earlier lessons help. Open one if a later sentence is hard to follow.

They never stop moving — particles keep moving, even with no push.
Three arrangements — solid, liquid and gas pack the same particles differently.
Reflection's law — light leaves a surface at the angle it arrived.
A rate — compare two kinds of amount, keeping units.
How fast, not just how far — speed compares distance against time.

Nothing here makes a loud sound. Every wave is drawn on the screen.