The tide generating force arises from
Answer: A
It is the residual after the mean gravitational attraction is balanced by the orbital acceleration. This residual is what produces two bulges rather than one, on opposite sides of the Earth. Both bulges are carried round as the Earth rotates beneath them.
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Assertion (A): There are two tidal bulges rather than one on the Earth.
Reason (R): The tide generating force is a difference, so it points outward on both sides.
Answer: B
Both are true and the reason gives the cause, and this is why most coasts see two high waters a day. A simple attraction argument would predict only one bulge and one high water daily. The observed semidiurnal tide requires the difference form.
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The moon's tide generating force is roughly what multiple of the sun's?
Answer: C
The sun is far more massive but very much further away, and the force varies with the inverse cube of distance. The lunar contribution therefore dominates the tide by roughly a factor of two. Distance matters far more than mass in this calculation.
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Assertion (A): The sun contributes less to the tide than the moon despite its far greater mass.
Reason (R): The tide generating force falls off with the cube of distance rather than the square.
Answer: D
Both are true and the reason gives the dependence, and distance therefore outweighs mass here. The solar contribution is nonetheless large enough to produce the spring neap cycle. Reinforcement and cancellation give the fortnightly rhythm.
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Spring tides occur when
Answer: A
Correct answer: the sun and moon are aligned, at new moon and at full moon
When the sun and moon lie on the same line as seen from Earth, their tide-raising forces reinforce and the range is at its greatest. That happens twice a lunar month, at new moon and at full moon, so spring tides come roughly every fortnight. The name has nothing to do with the season - it refers to the water springing up.
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Neap tides occur when
Answer: B
Correct answer: the sun and moon are at right angles as seen from the Earth
At the quarter moons the sun and moon pull at right angles, so the solar tide partly cancels the lunar one and the range is at its least. Spring and neap tides therefore alternate at roughly weekly intervals. Distance in the orbit does affect the range, through perigee and apogee, but it is alignment that distinguishes springs from neaps.
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The interval between successive spring tides is approximately
Answer: C
Springs occur twice per synodic month of about 29.5 days, once at new moon and once at full. The half month interval is the origin of the fortnightly spring neap cycle familiar at every port. Two springs and two neaps occur in each month.
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Consider the following statements about spring and neap tides.
1. Springs occur at new moon and at full moon each month.
2. Neaps occur at the first and last quarters of the moon.
3. Springs take their name from the season of the year.
Answer: D
The first two are correct and describe the fortnightly cycle. The third is a common misunderstanding, since the word refers to the water springing up rather than to any season. Springs occur in every month of the year alike.
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Match each tidal regime with its description.
List I
A. Semidiurnal
B. Diurnal
C. Mixed semidiurnal
D. Mixed diurnal
List II
1. two unequal high waters each lunar day
2. two nearly equal high waters each lunar day
3. sometimes one and sometimes two high waters
4. a single high water and low water each lunar day
Answer: A
Which regime occurs at a site depends on the relative sizes of the constituents there. The form factor, comparing the diurnal and semidiurnal amplitudes, is used to classify them. The ratio is computed from the four principal constituents.
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The form factor used to classify a tidal regime is the ratio of
Answer: B
It is usually written as the sum of K1 and O1 divided by the sum of M2 and S2. Values below about 0.25 indicate a semidiurnal regime and values above three a diurnal one. Intermediate values indicate one of the two mixed regimes.
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