If you throw a rock in a puddle, the water will ripple because the disturbance moves radially outward from where it began; the water molecules merely move up and down. A wave includes four properties: amplitude (the size of displacement from the disturbance), wavelength (the distance from one disturbance to the next measured in meters), frequency (the number of waves that pass a stationary point, measured in cycles per second or Hertz), and wave speed (the product of wavelength and frequency, measured in meters per second). As a wave, light can expand and radiate in all directions, interfere with other waves, bend around corners, carry energy and momentum, and interact with matter.
