OCS 1005 Chapter : WAVES And Tides
15 Mar 2019
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WAVES
1) You should know what is transported by waves
• ENERGY
2) You should know what wavelength, height, frequency, and period are
• Wave period: The time it takes for a wave crest to travel one wavelength
• Wave length: The distance between the peak of two adjacent crests
• Wave frequency: The number of wave crests that pass a fixed point each second
• Wave height: The distance from the crest to the trough of a wave
3) You should know what Stokes drift is
• Stokes drift: The small net transport of water in the direction of a wave
4) You should know what the disturbing and restoring forces of different wave types are
• A disturbing force is an energy force that causes waves. A restoring force is an energy
source that returns the water surface to flatness after a wave has passed
5) You should know what the smallest and largest waves are
• Largest: Tides. Disturbing force is the gravitational attraction of the moon and sun and the
rotation of the Earth. The restoring force is gravity
• Smallest: Capillary waves. Disturbing force is wind and restoring force is the cohesion of
water molecules
6) You should know what types of waves contain most of the energy of the surface ocean
• Wind waves. Disturbing force is wind and the restoring force is gravity
7) You should know the equation that relates wavelength, period, and speed in deep-water waves and
how these parameters change over long distances and as deep-water waves move into shallow water
8) You should know why waves break and in what conditions this happens
9) You should know what dispersion is
• Dispersion is the process of wave separation by size (wavelength). This happens because waves
with greater wavelengths move faster--the speed of the waves are controlled by their wavelength
10) You should know what a wave train is and how it behaves
• A group of waves with the same wavelength
11) You should know what fetch is
•
12) You should know what a fully-developed sea is
13) You should know what affects wave size and were the largest waves in the oceans are typically found
14) You should know what interference is and what the possible outcomes are from this process
• Interference occurs when two wave trains interact. The waves can either cancel each other out
(destructive interference) or add together to create even larger waves (constructive interference
• When crests line up we get constructive interference.
• Crest and troughs are aligned we get destructive interference.
15) You should know what causes waves to refract and diffract
• The portion of the water that is in shallower water begins to interact with the bottom sooner than
the other portion of the wave does and this causes the Wave to be refracted and moved into
another direction. Bending away from the original direction. These waves will also crest before
the other waves.
• When waves encounter something like an island or another obstacle we can have the process of
diffraction. In this case waves are approaching the island and are refracted on either side of the
island. So on the backside of the island we can have constructive and destructive interference of
the two wave trains coming together. This can result in areas called LEES usually on the
backside of an island (waves are far smaller).
• Constructive interference can also produce larger waves than the original wave trains. And so a
shore line may be pounded with waves that are far stronger.
• Early Polynesian explores used this to determine the location of islands they couldn’t see****
16) You should know what a standing wave is and what causes it
• A standing wave is a wave that oscillates around a single node--the wave has crests and troughs
in a fixed position. This occurs when a wave strikes an obstacle directly and the reflected waves
interfere with the oncoming waves
• If a wave strikes an obstacle directly, the reflected waves interfere with oncoming waves and
create a standing wave.
• As the crest of the wave reaches one side and is reflected backwards, the water flows back in the
opposite direction creating a crest on the other side of the basin.
• Node- an area where there is basically NO motion happening. There is no rise or fall of water
• All happens because of constructive and destructive interference.
• Good example is a SEICHE
17) You should know what a seiche is and what causes it
• A seiche occurs when water sloshes back and forth in a closed basin, like a lake. It occurs
due to changes in atmospheric pressure (most common), storm surge, or a tsunami
Document Summary
A restoring force is an energy source that returns the water surface to flatness after a wave has passed: you should know what the smallest and largest waves are, largest: tides. Disturbing force is the gravitational attraction of the moon and sun and the rotation of the earth. The restoring force is gravity: smallest: capillary waves. Disturbing force is wind and restoring force is the cohesion of water molecules: you should know what types of waves contain most of the energy of the surface ocean, wind waves. These waves will also crest before the other waves: when waves encounter something like an island or another obstacle we can have the process of diffraction. In this case waves are approaching the island and are refracted on either side of the island. So on the backside of the island we can have constructive and destructive interference of the two wave trains coming together.
