Wave (physics) facts for kids

A wave is a kind of oscillation (disturbance) that travels through space and matter. Wave motions transfer energy from one place to another.

Examples

Waves are found everywhere in the natural world. Examples of waves:

sound

water waves
seismic wave (earthquakes)
electromagnetic wave
- light wave
- radio wave

Properties

Here is a picture of a sine wave.

Waves have properties that can be measured. All waves can be pictured by adding sine waves.

Sine waves can be measured too. The shape of a sine wave is given by its amplitude, phase, wavelength and frequency. The speed that the sine wave moves can be measured. The amplitude and wavelength of the sine wave is shown in the picture.

The highest point on a wave is called the peak. The lowest point is called the trough. The peak of a wave and the trough of a wave are always twice the wave's amplitude apart from each other. The part of the wave half way in between the peak and the trough is called the baseline.

Complicated wave forms (like the sound waves of music) can be made by adding up sine waves of different frequencies. This is how mp3 audio files are converted from their compressed form into music we can hear.

Waves and matter

Some waves can move through matter while others cannot. For instance, some waves can move through empty space, light waves for example. Sound waves, on the other hand, cannot move through empty space. Inherently, all waves carry energy from one place to another when they move. In some applications of technology, waves may carry meaningful information from one place to another, such as news on the radio.

Usually, after a wave moves through matter, the matter is the same as it was before the wave was introduced, though in some cases, matter can be affected by waves traveling through it. In 1922, Louis de Broglie found out that all waves are also particles, and all particles are also waves.

Types

In matter:

Transverse wave: the vibrations of particles are perpendicular ⊥ to the direction of travel of the wave. Transverse waves have crests and troughs. Wave crests and troughs move along a travelling transverse wave.
Longitudinal wave: the vibrations of particles are parallel to the direction of travel of wave. Longitudinal waves have compressions and rarefactions. Compressions and rarefactions move along a travelling longitudinal wave.
Standing wave: a wave that remains in a constant position.
Travelling wave: The blue waves move off to the right. They are traveling waves. The red waves do not move. They are standing waves.
Solitary wave: Solitary waves are hard to explain. They were first observed in a river channel in 1834. Something gets a bulge of water starting moving up the channel and the bulge on the surface of the water continues to move up the stream. At first, physicists did not believe the story they heard from the man who observed it.
Light waves can move through space. Light is different from wind or water because light sometimes acts like waves and sometimes it acts as little bits called "particles." The nature of light is a big part of quantum mechanics.

Transverse wave
Longitudinal wave
Standing waves
Travelling waves
Solitary wave

Related pages

List of wave topics

Images for kids

Animation of two waves, the green wave moves to the right while blue wave moves to the left, the net red wave amplitude at each point is the sum of the amplitudes of the individual waves. Note that f(x,t) + g(x,t) = u(x,t)
Amplitude modulation can be achieved through f(x,t) = 1.00*sin(2*pi/0.10*(x-1.00*t)) and g(x,t) = 1.00*sin(2*pi/0.11*(x-1.00*t))only the resultant is visible to improve clarity of waveform.
Sinusoidal waves correspond to simple harmonic motion.
Standing wave in stationary medium. The red dots represent the wave nodes
Light beam exhibiting reflection, refraction, transmission and dispersion when encountering a prism
$Wave refraction$

Sinusoidal traveling plane wave entering a region of lower wave velocity at an angle, illustrating the decrease in wavelength and change of direction (refraction) that results.
Schematic of light being dispersed by a prism. Click to see animation.
400px
300 px
A propagating wave packet; in general, the envelope of the wave packet moves at a different speed than the constituent waves.
Animation showing the effect of a cross-polarized gravitational wave on a ring of test particles
Frequency dispersion in groups of gravity waves on the surface of deep water. The red dot moves with the phase velocity, and the green dots propagate with the group velocity.
This shows a wave with the Group velocity and Phase velocity going in different directions.
One-dimensional standing waves; the fundamental mode and the first 5 overtones.
A two-dimensional standing wave on a disk; this is the fundamental mode.
A standing wave on a disk with two nodal lines crossing at the center; this is an overtone.