Waves are disturbances that transfer energy without transferring matter. When you drop a stone in a pond, the water does not travel outward. The wave pattern does. Sound waves travel through air as pressure variations. Light waves travel through space as oscillating electric and magnetic fields. Understanding waves is essential because so much of physics and engineering involves them.
Waves are characterized by wavelength, frequency, amplitude, and speed. Wavelength is the distance between successive crests. Frequency is the number of crests that pass a point per second, measured in hertz. Amplitude is the maximum displacement from equilibrium. Speed is how fast the wave pattern moves. The relationship is simple: speed equals frequency times wavelength. Our Wave Speed Calculator computes any one of these from the other two.
There are two main categories. Transverse waves oscillate perpendicular to the direction of travel, like waves on a string or light. Longitudinal waves oscillate parallel to the direction of travel, like sound in air. Some waves, like ocean waves and seismic waves, have both components.
Sound waves are longitudinal pressure waves. The speed of sound in air at room temperature is about 343 m/s, but it depends on temperature. In water, sound travels about 4.3 times faster. In steel, about 15 times faster. This is why you can hear a train coming through the rails before you hear it through the air. Our Speed of Sound Calculator accounts for temperature.
The Doppler effect is the change in frequency of a wave when the source or observer moves. An ambulance siren sounds higher as it approaches and lower as it recedes. Radar guns use the Doppler effect to measure vehicle speed. Astronomers use it to determine whether stars are moving toward or away from us. Red-shifted light from distant galaxies provided the first evidence that the universe is expanding. Our Doppler Effect Calculator computes observed frequencies.
Light is an electromagnetic wave. Its speed in a vacuum is 299,792,458 m/s, a number so precisely known that the meter is now defined in terms of it. Visible light has wavelengths from about 400 nm (violet) to 700 nm (red). Infrared is longer, ultraviolet is shorter. X-rays and gamma rays are even shorter. The energy of a photon is proportional to its frequency, given by E equals hf, where h is Planck’s constant.
Interference and diffraction are uniquely wave phenomena. When two waves meet, they can reinforce or cancel each other. Noise-canceling headphones exploit destructive interference by generating sound waves that are the inverse of ambient noise. Diffraction explains why you can hear someone around a corner but not see them. Sound waves bend around obstacles more than light because their wavelengths are comparable to everyday object sizes.