Measure a Wave
Instructions: Study the animation below and then scroll down to answer the questions that follow.
Now, answer the questions below.
- What is the wave period in the above animation?
The wave period in the animation is about 6 seconds
- What is the relationship between wavelength and period? As wavelength increases, how is wave period affected?
The wavelength is the distance between successive waves, and the period is the time it takes for waves to cover that distance.
- The approximate speed of a wave train can be calculated from the average period of the waves in the train, using a simple formula: speed (in knots, which are nautical miles per hour) = 1.5 x period (in seconds). If NOAA reports that a gale 400 nautical miles offshore has kicked up high waves with a period of 12 seconds, when should you go to the beach?
The speed of the wave train is 1.5 x 12, or 18 miles an hour. Since the waves are coming from 400 nautical miles away, they should star hitting the beach in just over 22 hours (400/18 = 22.22).
- What will happen to the wave period as the wave train reaches shallow water?
If the time it takes for successive wave crests to pass a point is constant even as the waves slow down, then the crests must get closer together, which means the wavelength decreases. As waves approach the shore, they bunch up, and the crests break in rapid succession.