Twister_Ken
Well-Known Member
Four rivers and an awful lot of foreshore* not to mention a BIG surface area.
*or maybe a lot of awful foreshore - I've never been there.
explaining tides
- Thread starter dylanwinter
- Start date
Four rivers and an awful lot of foreshore* not to mention a BIG surface area.
*or maybe a lot of awful foreshore - I've never been there.
Cruiser2B
Well-Known Member
Tide change happens progressively, as the sun/moon changes relative positions - so the closer you are to the "centre" of the tide change, the faster the change in current direction. The gravitational pull of the sun/moon is not going to have a large effect on a relatively small body of water such as a river; the big "pull" is on the large bodies of water, so if you can imagine the centre of the ocean bulging up towards the sun/moon, you can picture that the pull at its periphery will be more gradual. That said, at the mouthes of rivers where the surface area increases rapidly, a small vertical movement translates into a much greater volume of water, so you're going to see a quicker turn, greater current speed and more turbulence. The same happens where the sea bottom drops off (depth increases dramatically); the vertical motion of tide then draws a lot more water off the adjacent shelf, so that's where you'll see eddies and whirlpools.
davidej
Well-Known Member
If tides caused by the pull of the moon (I know the sun , planets, etc also have some effect) why do we get two a day?
The only explanation I have seen came from a physics PhD and ran to about 3 pages of calculus.
The only explanation I have seen came from a physics PhD and ran to about 3 pages of calculus.
electrosys
Well-Known Member
The Earth has a centre of gravity - if there were no moon etc, the ocean's surface would be uniform.
Enter 'the moon' ... exerting a gravitational pull, which as we all know causes a bulge of water to be attracted towards it.
That will (or would...) cause a shift in the Earth's centre of gravity towards it.
On the other side of the globe, there is a reduction in gravitational force on the hitherto uniform ocean's surface - which allows a bulge of water to form, of exactly the same height as on the 'moon's side' - thus the Earth's centre of gravity is restored .... and we can all sleep easy in our beds.
2 bulges = 2 tides per day (except in those known 'awkward ' places, where 4 a day occur. Of course they pay higher rates of Council Tax for that priviledge ...).
dylanwinter
Well-Known Member
I have thoroughly enjoyed
I have thoroughly enjoyed the wash
it is a bit dull at high tide but at low tide - once the edge comes closer it is wonderful
and never been anywhere where the human and avian aerobatics have been so spectacular
great light at times as well
but most of us like to think we sail in a good place and sometimes find it hard to see what other sailors see in their chosen sailing areas.
As I went up the thames - motoring all the way into a headwind I came across some of those london yacht clubs
greenwhich and gravesend
then coming back down the thames withe the wind behind me, the sun shining and the engine off I suddenly understood why they sailed there
challenging, interesting and close to home as well
Dylan
I have thoroughly enjoyed the wash
it is a bit dull at high tide but at low tide - once the edge comes closer it is wonderful
and never been anywhere where the human and avian aerobatics have been so spectacular
great light at times as well
but most of us like to think we sail in a good place and sometimes find it hard to see what other sailors see in their chosen sailing areas.
As I went up the thames - motoring all the way into a headwind I came across some of those london yacht clubs
greenwhich and gravesend
then coming back down the thames withe the wind behind me, the sun shining and the engine off I suddenly understood why they sailed there
challenging, interesting and close to home as well
Dylan
davidej
Well-Known Member
Not really so - the earth and moon each revolve around their combined CofG which is somewhere near the earth's but not quite. This crates a centrifugal force which must be balancey by gravity, which or course is less on the bulge.............
Discuss
awol
Well-Known Member
davidej
Well-Known Member
That doesn't explain amphidromes
I've looked this up
...which explains why the PhD took three pages of calculus
and Dylan
will you stop bringing us down to earth - metaphorically speaking!