Unit 9 Overview of Topics

9.1 What Causes Ocean Tides?

  • forces

    • gravitational force

    • centripetal force

    • sun and moon forces

  • resultant forces

  • tide-generating forces

    • nadir

    • zenith

    • “equator”

  • tidal bulges

    • moon and sun

    • lunar day vs. solar day

  • earth’s rotation and the tides

    • flood tide

    • ebb tide

(1) why are there tidal bulges on both sides of earth?

(2) explain why the sun’s influence on earth’s tides is only 46% that of the moon, even though the sun is so much more massive than the moon?

(3) why is a lunar day 24 hrs, 50 min long, while a solar day is 24 hrs long?

(4) if earth didn’t have the moon orbiting it, would there still be tides? why or why not?

9.2 How do tides vary during a monthly tidal cycle?

  • monthly tidal cycle

    • new moon

    • full moon

    • quarter moon

    • tidal range

    • spring tide

    • neap tide

    • waxing crescent, waxing gibbous, waning gibbous, waning crescent

    • why does the moon appear to change phase?

  • complicating factors

    • declination of moon and sun

    • ecliptic

    • elliptical orbits: perihelion, aphelion, perigee, apogee

    • proxigean

  • idealized tide prediction

    • when is high tide? low tide?

(1) Diagram the Earth–Moon system’s orbit about the Sun. Label the positions on the orbit at which the Moon and Sun are closest to and farthest from Earth, stating the terms used to identify them. Discuss the effects of the Moon’s and Earth’s positions on Earth’s tides.

(2) Explain why the maximum tidal range (spring tide) occurs during new and full moon phases and the minimum tidal range (neap tide) at first-quarter and third-quarter moons.

(3) What is declination? Discuss the degree of declination of the Moon and Sun relative to Earth’s equator. What are the effects of declination of the Moon and Sun on the tides?

(4) Diagram the Earth–Moon system’s orbit about the Sun. Label the positions on the orbit at which the Moon and Sun are closest to and farthest from Earth, stating the terms used to identify them. Discuss the effects of the Moon’s and Earth’s positions on Earth’s tides.

9.3 What do tides look like in the ocean?

  • amphidromic points

  • cotidal lines

  • effect of the continents

  • deep/shallow water effect on tides

  • other considerations

(1) Are tides considered deep-water waves anywhere in the ocean? Why or why not?

(2) What are amphidromic points and cotidal lines?

(3) Discuss reasons why tides don’t follow a simple tidal bulge model.

9.4 What types of tidal patterns exist?

  • diurnal

    • tidal period

    • # high and low tides

  • semidiurnal

    • tidal period

    • # high and low tides

  • mixed

    • tidal period

    • # high and low tides

  • why don’t all areas of the world experience the same tidal pattern?

(1) What do the terms diurnal, semidiurnal, and mixed mean, as related to tidal patterns?

(2) Describe the number of high and low tides in a lunar day, the period, and any inequality of the following tidal patterns: diurnal, semidiurnal, and mixed.

(3) Using the Internet, find a coastal tidal prediction for your birthday this year (or, if your birthday has already happened, find next year’s tide prediction). What tidal pattern is displayed?

(4) Of the three tidal patterns, which one is most common along the U.S. East Coast? The U.S. West Coast? Worldwide?

9.5 What tidal phenomena occur in coastal regions?

  • Bay of Fundy

  • coastal tidal currents

    • rotary current

    • reversing current

    • flood current

    • ebb current

    • high slack water

    • low slack water

  • whirlpools

  • grunions

(1) Discuss factors that help produce the world’s largest tidal range in the Bay of Fundy.

(2) Specify the differences between rotary and reversing tidal currents.

(3) Of flood current, ebb current, high slack water, and low slack water, when is the best time to enter a bay by boat? When is the best time to navigate in a shallow, rocky harbor? Explain.

(4) Describe the spawning cycle of grunion, indicating the relationship among tidal phenomena, where grunion lay their eggs, and the movement of sand on the beach.

9.6 Can tidal power be harnessed as a source of energy?

  • advantages of tidal energy

  • disadvantages of tidal energy

  • tidal power plants

    • examples

  • how do tidal power plants work

(1) Discuss at least two positive and two negative factors related to tidal power generation.

(2) Explain how a tidal power plant works, using as an example an estuary that has a mixed tidal pattern. Why does potential for usable tidal energy increase with an increase in the tidal range?