Wave properties: amplitude, wavelength and frequency

A wave's speed equals its frequency multiplied by its wavelength — how many oscillations pass a point each second, times how much space each one takes up. Get the speed and one of the other two, and the third falls straight out.

For a wave whose speed is fixed by the medium it travels through — like sound in air, or light in a vacuum — frequency and wavelength are locked in a seesaw. Raise the frequency and the wavelength must shrink to match, since the speed itself can't budge; that's a direct consequence of the same equation, not a separate rule to memorise.

It's tempting to think that changing a wave's amplitude — how big its oscillations are — should also change its frequency or speed, but amplitude is independent of both. A loud sound and a quiet sound of the same pitch share the same frequency and travel at the same speed; only their amplitude differs.