Waves

Energy moving without matter moving.

Describing a wave

Wavelength is the distance between peaks, frequency is how many pass per second in hertz, and amplitude is the height. Speed equals frequency times wavelength.

In a transverse wave the motion is across the direction of travel; in a longitudinal wave it is along it.
Sound is longitudinal, light is transverse.

What waves do

They reflect off surfaces, refract when entering a new material, and interfere when they meet, adding where peaks line up and cancelling where a peak meets a trough.