MS20 Laboratory: Waves on the Oceans



|MS 20 Introduction To Oceanography |

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|Waves |

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A. Determining shallow-water wave speed as a function of depth

|Table A: |

|Depth |Time in Seconds | |Calculated Velocity | |Theoretical Velocity |

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|Depth |Time in Seconds/10 | |Period | |Theoretical Period |

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| |a | |b | |(average of a & b) | |from equation X |

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|10 cm | | | | | | | |

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|15 cm | | | | | | | |

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|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?

C. Determining the period of a standing wave

|Table C: |

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| |Internal wave | |Surface wave |

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|Wave speed | | | |

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|Wave height | | | |

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|d1 | |h1 | |

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|d2 | |h2 | |

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|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

D1: Fine grained ripple pattern

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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)

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How do the ripple forms relate to the horizontal currents. (hint: examine wave length and wave height)

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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?

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What do you observe happening to the wavelengths as the waves move from the deeper to shallower areas?

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Would waves of a longer length be slowed down further offshore than shorter waves? Explain.

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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.

[pic]

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