January 21 lecture Flashcards
What are Waves?
Waves are energy transmitted through matter
Does the medium move as energy passes through it?
No, the medium dose not move as energy passes through it but constituent particles oscillate in place as the energy passes through them
How do waves move through matter?
In the the 3d
What are progressive waves?
Waves where the wave from can be seen travelling through the medium
What two forces cause waves?
Disturbing forces
restoring forces
What is a disturbing force?
A disturbing force that modifies a ‘undisturbed’ medium to create the wave
What are the most common disturbing forces?
Most common such force is the wind that blows over the surface and transfers energy to the ocean
What are restoring forces?
A restoring force that tends to bring a system to its undisturbed state
What is the restoring force for a liquid
Gravity
What is the point of highest elevation on a wave?
The crest
What is the depression between each pair of crests called?
the trough
What is the distance between each successive pair of crests or troughs called?
The wavelength
What represents wavelength
λ (Lambda)
What is the vertical distance between crests and trough?
Height, represented as H
What is the vertical distance between crests and trough and the MEAN water level?
The amplitude. (H/2)
What is a wave period? (T)
It is the time it takes fro a wave to move a distance equal to one wavelength.
or
The time between the arrival of two successive crests or troughs at a given location.
What is a waves frequency?
the number of crest or troughs that pass a point in a fixed unit of time. (f)
How are period and frequency related?
T = 1/f
What is wave speed (C)?
It is related to the speed of ‘movement’ of a wave crest.
What is the equation for wave speed?
C = λ/T
What is Wave Steepness?
The ratio of the wave height to the wavelength (H/λ)
When waves move across the ocean unbroken is there any net movement of the water?
There is no net forward motion of the water itself, only energy associated with the wave from within the wave moves.
What is Stokes Drift?
When the forward speed of the crest is faster than the backwards speed at the base of the trough due to particle speed decreasing with depth.
So particles will move slightly farther forward at the crest than they move back at the trough
What 5 things create waves?
- ) interactions of wind with the oceans surface
- ) Impacts on the ocean
- )Tidal interactions
- ) Passage of vessel or marine mammals
- ) Density interfaces within the ocean or on the surface ( internal waves )
What happens to wave shape over time?
They go from more regular Sinuoidal form to the trochoidal shape
What is a Sinusoidal wave?
a regular rounded wave shape
What is a trochoidal wave shape?
pointed crests and rounded troughs
When waves get too steep they will break, at what height to wavelength ratio will this happen?
1:7 of HIght:Wavelengths
Winds never blow uniformly over the ocean, how does this affect wave formation? what is the result called?
We get waves of many heights, wavelengths, periods, directions. This is called the SEA
What is a swell?
It is where waves are generally smooth, from the same direction and have the same wavelength
What does wave height depend on?
Wind speed, wind fetch, wind duration and water depth.
In the open ocean what travels faster Longer waves or Shorter waves
Longer waves travel faster
What is wave dispersion?
When longer waves move faster than shorter waves in the ocean.
