Download MS20 Laboratory: Waves on the Oceans

Earth Science Laboratory
Waves
Lab Section
Name
Date
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MS20 Laboratory: Waves on the Oceans
Answer sheet: record all data in the appropriate metric units (centimeters, grams, etc.).
Remember to use significant figure rules and to indicate appropriate units (if the scale
reads 13.4 g, your answer is not 13.4, but 13.4 g (or 13.4 grams).
A.
Determining shallow-water wave speed as a function of depth
TABLE A:
DEPTH
TIME IN SECONDS (T)
MEASURED
VELOCITY
THEORETICAL
VELOCITY
Average
L/T
from equation 7
1 cm
3.8
2 cm
2.8
3 cm
2.3
120/3.8=31.6
cm/s
120/2.8= 42.9
cm/s
52.3 cm/s
54.21 cm/s
4 cm
2.0
60 cm/s
62.6 cm/s
a
Revised on 4/17/2007
b
31.3 cm/s
44.26 cm/s
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Earth Science Laboratory
Waves
Figure A
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.
This formula is for Earth (in m/sec2) 3.13 is the square root of
9.8 m/s2. Since Martian gravity is less than 1/3 that of Earth, C should be less
than 1/3.
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?
Solve for L
C = L/T (equation 1)
C= 12.5 m/sec (given in the problem)
C = 1.56 T (equation 4)
So combining the above 2 equations
1.56 T = 12.5 m/sec
T=8
L=C XT
L = 12.5m/sec X 8 sec
L= 100
Wave base = ½ L or 50
meters
(equation 3)
12.5 m/sec = 1.25 x √L
156.25 =1.56 L
100 = L
Revised on 4/17/2007
Page 2 of 4
Earth Science Laboratory
B.
Waves
Determining the period of a standing wave
TABLE B:
DEPTH
TIME IN SECONDS/10
PERIOD
THEORETICAL PERIOD
a
b
(average of a & b)
from equation 8
10 cm
12.5
12.7
1.265
1.21 sec
15 cm
11
11
1.1
0.99sec
20 cm
10
10
1.00
0.86 sec
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.
2 * 2000M / square root of 9.8m/sec2 * 40m =4000m/19.8m/sec = 202sec
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?
Revised on 4/17/2007
Page 3 of 4
Earth Science Laboratory
C.
Waves
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.
Revised on 4/17/2007
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