What Is Wavelength

When you watch waves move across water, you can see high points and low points. The high point of a wave is called the crest. A crest is the top part of a wave where the water rises highest. Wavelength is the distance from one crest to the next crest. Scientists measure wavelength to understand how waves are different from each other.

Not all waves have the same wavelength. Some waves have long wavelengths, which means the crests are far apart. Imagine standing at a lake on a calm day. The waves might be gentle and spread out, with lots of space between each crest. These waves have long wavelengths. Other waves have short wavelengths, which means the crests are close together. Think about dropping a pebble in a puddle. The ripples that form have crests very close to each other. These ripples have short wavelengths.

Understanding wavelength helps us describe and compare different types of waves. When you look at ocean waves, you might notice that some days the waves are big and far apart, while other days they are small and close together. The distance between the crests—the wavelength—is one important way waves can be different. Whether in a bathtub, a swimming pool, or the ocean, all water waves have wavelengths that we can observe and measure.