Chapter 9 (Tides)
It is Thursday and an angler is planning a fishing trip in two days on Saturday. The angler knows from experience that the fishing is best at a particular location at the beginning of high tide. He does not have a tide table, but the angler noted that the high tide on Thursday was at 12:15 PM. At what time on Saturday should he plan to arrive to start fishing, assuming that this location has a diurnal tide type?
1:55 PM High tide (or any part of the tide cycle) is 50 minutes later each solar day, so the time of high tide on Saturday will be about 100 minutes (1 hour 40 minutes) later than on Thursday.
How many spring and neap tides will a tide-recording station experience in a given month?
2 spring tides and 2 neap tides
A lunar day is __________ in duration.
24 hours and 50 minutes
It is Wednesday, and you are planning a fishing trip for this coming Saturday. You have heard that fishing is best at your chosen spot when the ebb current begins to flow, so you wish to start fishing at high tide. You do not have a tide table, but you have noted that today's high tide was at 1:10 p.m. At what time on Saturday should you plan to arrive and start fishing?
3:40pm
Which of the following statements about tides in a simple tidal bulge model is/are true? Choose all that apply.
A lunar or solar eclipse can occur only when the Moon is in syzygy. Tides are greatest when the Moon is at perigee and Earth is at perihelion. Spring tides result from constructive interference between the solar and lunar tidal bulges. Neap tides result from destructive interference between the solar and lunar tidal bulges.
Which of the following statements about tidal patterns and tidal charts is/are true? Choose all that apply.
A semidiurnal tidal pattern has two low tides every tidal day. A mixed tidal pattern has two lows of unequal height and two highs of unequal height every tidal day. The tidal range is the difference in height between a high tide and a low tide. A tidal day is 24 hours and 50 minutes long.
This image depicts the orbital relationships of the Sun, the Moon, and Earth. Match the correct letters to the following positions of the Moon and Earth.
A: Apogee (left of Earth) D: Aphelion (left of sun) B: Perihelion (right of sun) C: Perigee (right of Earth)
Why does the Moon generate larger tidal forces than the Sun?
Although the Sun is bigger, the Moon is much closer.
On the image below, match the letter to the correct tidal pattern or tide chart feature.
B: Area with semidiurnal tidal pattern (arrow pointing right from Africa) C: Area with mixed tidal pattern (arrow pointing down/right from South America) E: Tidal range (middle chart) D: Datum (bottom chart) F: Tidal period (top chart) A: Area with diurnal tidal pattern (arrow pointing up/right from USA)
The diagram below shows the position of the Earth-Moon-Sun system during neap tide conditions. Match the correct letters to the following items.
C: Lunar tidal bulges (bottom of Earth) D: First-quarter moon (above Earth) B: Third- or last-quarter moon (below Earth) A: Solar tidal bulges (top of Earth)
neap tide conditions
C: Lunar tidal bulges (bottom of Earth) D: First-quarter moon (above Earth) B: Third- or last-quarter moon (below Earth) A: Solar tidal bulges (top of Earth)
The image below shows the various positions of the Moon as it orbits Earth (north polar view). Correctly match the letters with the corresponding phases of the Moon.
D: Waxing gibbous (top left from Earth) B: Waxing crescent (top right from Earth) C: Waning crescent (bottom right from Earth) A: Waning gibbous (bottom left from Earth)
Of the following statements about the location of the barycenter of the Earth-Moon system, which is/are true? Choose all that apply.
It is located at a point beneath Earth's surface within the mantle. It is located at the center of mass of the Earth-Moon system.
Of the following statements about forces and tidal bulges, which is/are true? Choose all that apply.
On the side of Earth closest to the Moon, a tidal bulge will form as a result of an excess of gravitational force. On the side of Earth facing away from the Sun, a tidal bulge will form due to an excess of centripetal force. Tidal bulges are produced on both sides of Earth from the Moon and the Sun.
Of the following statements about lunar phases, which is/are true? Choose all that apply.
Over the few days of a waxing crescent moon, the tidal range decreases. Over the few days of a waxing gibbous moon, the tidal range increases.
Of the following statements about the contribution of the Sun and the Moon to Earth's tides, which is/are true? Choose all that apply.
The Moon exerts over twice the gravitational pull of the Sun on Earth's tides because of its proximity to Earth. The Sun's contribution to the tides is less than that of the Moon. The lunar tidal bulges are about twice the size of the solar tidal bulges.
Of the following statements about the force of gravity between two bodies, which is/are true? Choose all that apply.
The force of gravity between two bodies decreases as distance increases. The force of gravity between two bodies increases with an increase in mass. The force of gravity between two bodies is most affected by a change in distance.
Of the following statements about the monthly tidal cycle, which is/are true? Choose all that apply.
The full moon and the new moon affect the tides about the same. Neap tides occur twice a month. The full moon is associated with spring tide conditions. Spring tides occur twice a month.
How is a semidiurnal period related to a tidal day?
The semidiurnal period is half as long as a tidal day.
Why are high tides found simultaneously on opposite sides of Earth?
The tidal bulges occur on both sides of Earth that are aligned with the tide-generating body.
Of the following statements about the tides, which is/are true? Choose all that apply.
There are two tidal bulges on Earth caused by the Moon: one facing the Moon, and the other facing away from the Moon. The tides are caused by an imbalance between the centripetal force and the gravitational force of the Moon and the Sun. Although we observe the tides coming in and going out, in reality, Earth is rotating into and out of various tidal bulges, which produces changing tides. Both Earth and the Moon orbit around their common center of mass, called the barycenter.
A grunion "run" would be expected within a few nights after
a new or full moon
A relatively small tidal range could be expected
at an amphidromic point
Tides occur on Earth because of an imbalance between gravity and
centripetal force
What are Earth's three different tidal patterns called?
diurnal, semidiurnal, and mixed
A boat is most likely to be carried out to sea from a harbor by a(n)
ebb current
On the side of Earth closest to the Moon, gravitational forces __________ the centripetal forces.
exceed On the side of Earth closest to the Moon, the gravitational forces exceed the centripetal forces because gravitational attraction is strongly influenced by the distance between two bodies.
How many semidiurnal tides would you expect during one tidal period?
four tides
What pattern of tides would you expect to see for a mixed tidal system?
four tides of different heights
The Moon's influence on Earth's tides is __________ the influence of the Sun
greater than Although the Moon is much smaller than the Sun, it is much closer to Earth, and hence exerts about twice the pulling effect (gravitational attraction) on Earth as the Sun does. In other words, solar tides are about 46% of the lunar tides.
Disadvantages of tidal power plants relative to conventional thermal plants include higher initial plant costs, periodicity of tidal currents, and
impacts on the marine environment
The most important factor that causes ocean tides on Earth is the
moon
The weakest gravitational force caused by the Moon is called the __________, which is found at the point on Earth farthest from the Moon
nadir The gravitational attraction between the Moon and Earth is weakest at the point farthest from the Moon.
What do we call the tide that occurs when destructive interference between lunar and solar bulges produces a small tidal range?
neap tide
A centrifugal force is one that is directed _____ and a centripetal force is one that is directed _____.
outward; inward
You have just arrived for a vacation on the Oregon coast, and you wish to explore some tide pools while you are there. You hear the local weatherman say that there will be a minus tide at 7 a.m. tomorrow. You should
set your alarm to wake you early; this may be your best chance for tide pooling
What do we call the tide that occurs when constructive interference between lunar and solar bulges produces a large tidal range?
spring tide
Some of the tide height numbers in your tide table are preceded by minus signs (or in some cases printed in red). This tells you that
spring tides are occurring
A proxigean tide occurs when
the Moon is at perigee at a time of syzygy
What are tides?
the regular daily rises and falls in sea level caused by the gravitational attraction of the Moon and Sun on Earth
Tidal forces result in two tidal bulges because __________.
the supplied gravitational forces at various points within the planet differ from the centripetal force
The tides are considered an example of shallow-water waves because the tidal bulges have a wavelength that is on the order of
thousands of kilometers
If the side of Earth that faces the Moon experiences a tidal bulge (high tide), then the opposite side of Earth will experience a
tidal bulge or high tide
The low and high tides experienced on Earth are the result of
tidal bulges
What do we call the time that passes between two high tides?
tidal period
Resultant forces result in __________ tidal bulge(s) on Earth.
two Resultant forces cause two tidal bulges to occur, one each on opposite sides of Earth.
How many diurnal tides would you expect during one tidal period?
two tides
The gravitational force exerted on Earth by the Moon is greatest at the
zenith
