A wave also has a "frequency". The frequency is how often a crest goes by. The frequency of a wave depends on how fast the wave is moving. It also depends on the wavelength of the wave. Imagine two sets of waves that have the same speed. If one set has a longer wavelength, it will have a lower frequency (more time between waves). If the other set has a shorter wavelength, it will have a higher frequency (less time between waves). Wavelength and frequency go opposite of each other. Shorter wavelengths mean higher frequencies, while longer wavelengths mean lower frequencies.
Sound waves with a wavelength around 34 cm (about a foot) have a frequency of 1,000 hertz. A hertz is one wave per second. So a thousand sound waves can enter your ear in a second! Sound waves travel much faster than normal water waves. Sound waves move through the air at around 343 meters/second (767 miles/hour).
Light moves even faster AND has shorter wavelengths. These combine to give light extremely high frequencies. Red light has a wavelength of about 682 nanometers. Its frequency is around 440 terahertz. That's 440,000,000,000,000 hertz. That's a whole lot of waves going by in a second!
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