Overview of Waves

A wave is a disturbance that carries energy from one place to another without permanently moving the material it passes through. When you drop a stone in water, the ripple spreads outward while the water itself mostly stays in place. Waves are one of the main ways that energy travels in nature.

There are two broad families of waves: mechanical waves, which need a material to travel through, and electromagnetic waves, which can travel through empty space.

Properties of a wave

Waves are described by a few key measurements. The wavelength is the distance between one peak and the next. The frequency is how many waves pass a point each second, measured in hertz. The amplitude is the height of the wave, which relates to its energy. The speed of a wave equals its frequency multiplied by its wavelength. The general subject of how waves move is covered in the lesson on wave motion.

Mechanical and electromagnetic waves

Mechanical waves, such as sound waves and water waves, require a medium like air, water, or a solid to travel through. Sound, for example, cannot travel through a vacuum. Electromagnetic waves, such as light, radio waves, and X-rays, are made of vibrating electric and magnetic fields and can travel through the vacuum of space; these are described in the lesson on electromagnetic waves. Waves are also classed as transverse, where the vibration is at right angles to the direction of travel, or longitudinal, where the vibration is along the direction of travel, as in sound.

How waves behave

Waves can reflect off surfaces, bend when they pass from one material to another, spread out as they pass an edge or opening, and combine with one another to reinforce or cancel out. When a wave source and an observer move relative to each other, the observed frequency changes; this is the Doppler effect, heard when a siren rises and falls in pitch as a vehicle passes.