MS 20 Introduction To Oceanography
Waves
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A.
Determining shallow-water wave speed as a function of depth
TABLE A:
DEPTH
TIME IN SECONDS
a
1 cm
b
Average
CALCULATED
VELOCITY
THEORETICAL
VELOCITY
L/T
from equation 6
31.3 cm/s
2 cm
3 cm
4 cm
On the following graph, plot measured wave speed (solid line) against theoretical wave
speed (dashed line).
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The gravity on Mars is about one fourth that on Earth (2.5 m/s2 instead of 9.8 m/s2). If
there were an ocean on Mars in the past, would you expect a wave traveling through
shallow water to move faster or more slowly than on the Earth? Explain your answer.
You have a deep-water wave moving onto shore with a with a wave speed of 12.5
meters per second. The period of the wave is S seconds. At what water depth will
this wave begin to first interact with the sea bed?
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B.
Determining the period of a standing wave
TABLE B:
DEPTH
TIME IN SECONDS/10
a
b
PERIOD
THEORETICAL PERIOD
(average of a & b)
from equation X
10 cm
15 cm
20 cm
The formula for the period of a standing wave is similar to the formula for a shallow water
wave, the only difference being the factor of two. Make a sketch below to show why two
basin lengths are needed to determine the standing wave period.
You live on a narrow lake, 2000 m long and 40 m deep. What would be the period
of the standing wave in the lake in seconds? Show your work.
Make a sketch of the lake from the side, and indicate where on this lake would you
experience maximum water-level fluctuations? Maximum horizontal currents?
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C.
Determining the period of a standing wave
TABLE C:
Internal wave
Surface wave
WAVE SPEED
WAVE HEIGHT
d1
h1
d2
h2
Theoretical wave speed
Why is there such a large difference between the wave height of the internal wave and
the surface wave ?
If two fluids were closer in density than those used in this experiment, would you expect
larger or smaller internal waves given the same input of energy? Explain!
D.
Ripple marks in sediment
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D1: Fine grained ripple pattern
D2: Coarse grained ripple pattern
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Where are the maximum horizontal currents on the aquarium bottom? Minimum? (hint:
maximum displacement of the sand indicates high currents)
How do the ripple forms relate to the horizontal currents. (hint: examine wave length and
wave height)
Observe the ripple patterns and comment on the relationship between the creation of
ripple forms and grain size. (hint: the currents are exactly the same in the two aquaria.)
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E.
Relationship between wavelength and water depth
What do you observe happening to the wave speed as the waves approach the shoaling
area?
What do you observe happening to the wavelengths as the waves move from the
deeper to shallower areas?
Would waves of a longer length be slowed down further offshore than shorter waves?
Explain.
F. Refraction of waves
How does the angle of the wave change as the waves move from deeper water into
shallower water. Explain why this happens.
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G.
Wave interference
The figure below shows two wave trains from two different storms passing through one
another. For each of the waves (A and B) identify the period and maximum and
minimum wave heights and enter the data on the figure below. Also plot the resultant
wave.
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