Tides Flashcards
What are tides essentially?
The Earth’s interaction with the moon and the Sun.
What is Newton’s law of universal gravitation?
There is a relationship between two bodies of a certain mass and the radius between them.
They exert a force on each other.
What does the force exerted in Newton’s law of universal gravitation effect?
Both the Earth’s crust and the oceans.
What are spring tides?
When the sun and the moon are lined up with the earth and they’re both pulling ‘out’ (their forces are aligned). O 0 o
Tidal forces of the Moon are reinforced by the Sun’s producing higher than average high tides and lower than average low tides.
The net effect of this is to increase the tidal range.
What are neap tides?
When the sun and moon are at right angles to each other.
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Moon’s tidal forces are partially cancelled out by the Sun’s.
Height of the high tides is lowered and the tidal range is reduced.
Why do we get two high tides a day?
Two bulges
First high tide: effect of the centrifugal force on the ocean, a result of the Earth orbiting round the centre of gravity between it and the moon (wins out ever so slightly, enough to make the oceans bulge out again on this side).
Second high tide: standard gravitational pull of the moon on the ocean.
What does the earth being tilted mean for tides?
Equal high tides at the equator.
Unequal high tides at higher latitudes.
Tidal timings not the same everywhere.
Continents get in the way of where the ocean goes- constrained by land masses
What is Newton’s first law?
All objects in motion stay in motion unless acted upon by an external force.
The result of the tilt of the earth, the interference of the continents and the rotating frame of reference results in…
Amphidromes (nodes)
The oceans of the earth sloshing around
The shape of a basin affects…
How long the wave of water takes to make its way around.
Resonance
Combine natural basin resonance with frequency of tidal “sloshing”
If they are additive, then amplitude of motion (tide) will increase.
What’s a tidal bore?
A large wave or bore caused by the constriction of the spring tide as it enters a long, narrow, shallow inlet.
Semi-diurnal
Diurnal
Mixed
2 unequal highs and lows
1 high and low
Double highs, etc
Where a section of the earth points towards the moon, then a high tide will occur as gravity pulls the ocean towards the moon. As well as creating the high tide there, the area on the opposite side of the earth, facing away from the moon will also have a high tide at the same time. This occurs as a result of…
The areas at 90-degree angle to the moon at this time will experience
inertia and centrifugal force, as the gravitational pull is weaker here and the ocean bulges out as a result.
low tides.
Why is the moon’s gravity weak at the surface of the Earth?
On average, the Moon is 385,000km from the Earth so, thanks to the inverse square law, the Moon’s gravity is very weak at the surface of the Earth.
It gets even weaker though when we move to the side of the Earth facing away from the Moon.
On this side of the Earth, there’s another 12,800km between the Moon and the surface and so the Moon’s gravitational field at the Earth’s surface is ~90% of what it is on the side facing the Moon.
How do tidal forces arise?
The difference in the Moon’s gravitational field across the Earth.
On the side of the Earth facing the Moon, the Moon’s gravitational field is strong enough to attract the water on this side towards it, creating an ever so slight tidal bulge.
This tidal bulge is what we associate with a high tide.
