High tides

[SteveG]

Why do we experience High and low tides and do opposing land masses alternate tides ?? If so what is the shortest alternation and the longest.

[Quizmonster]

Here's an answer to at least part of your question...Tides are caused by the gravitational pull of the moon and a 'tidal day' lasts 24 hours 50 minutes. Successive high tides occur 12 hours 25 minutes apart because of the orbit of the moon around the earth. There is a 'bulge' in the waters of earth directly beneath the moon, known as the direct tide and a corresponding 'bulge' on the opposite side of the world, known as the opposite tide. It's a bit of a paradox, but the 'lowering' of the water-level at the low-tide positions actually leads to an accumulation of water not only on the side of the earth nearest the moon but also on the side furthest away.

[SteveG]

Thank you QM, after such an spendid explaination it does rather render the latter part of my question invalid, cheers.

[sddsddean]

The sun also has some influence and the highest, or spring, tides are when the sun and moon are both on the same side of the Earth. Converesly, the lowest (neep) tides are when they are on opposite sides.

[thekraut]

The corresponding 'bulge' on the opposite side, as QM put it, is caused by the centrifugal force from the earth's rotation around the center of gravity of the moon/earth system. so no paradox there

[Gef]

for sddsdean - excellent answer but I think you will find that it's called a "neap" tide. A "neep"' is a vegetable.

[bellmeister]

sddsddean was almost right in his answer about spring and neap tides but not quite. Spring tides occur when the sun and moon are in line (i.e. they can be on the same side of the earth or on opposite sides). Neap tides occur when they are at right angles. Hence spring tides occur at (a day or two after to be precise) full AND new moon. Neaps occur just after first and third quarter phases of the moon.