“…the water pressure is applied in all directions, top and bottom (and sides) so there is no force that is pushing the glass downwards..”.

Except gravity.

Haha good one Martin!

But Daphne sorry your physics lesson is faulty, however C Falzon got in there before me and has explained it perfectly.

Unless the glass pane is perfectly sealed to the bottom – and I mean sealed, with a rubber seal – AND the existing pressure subsequently relieved, from beneath – the water pressure is applied in all directions, top and bottom (and sides) so there is no force that is pushing the glass downwards, in fact, again as C Falzon pointed out, there is buoyancy.

But “FFS” – wait till the summer and two persons with goggles will surely be able to lift it out. Gejja bis-CPD!!

So to to get it to float you have to make the water less buoyant than glass.

Calculate how many cubic metres of water you have in that pool. Add 100g of salt for every cubic meter of water. Then add 300g of sugar fr every cubuc meter of water.

Finally add ice cubes until the temperature of the water is brought down to 4 degrees Celsius, making it even denser than glass.

Your glass table top will then float to the surface. Then throw in one thousand tea bags per cubic metre from the shallow end and heat the water by plunging in a few radiator heaters at the deep end till boiling temperature. You now have a giant teapot as well.

Prosit. Best solution to date.

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I don’t need a physics lesson I can assure you. If you attach two vacuum cups, these are what glaziers use to lift plate glass in case you don’t know, to one edge of the glass then with someone on each cup you lift up and to the side at the same time. Don’t tell me you think that because the glass is on the bottom of a pool it can’t be moved because of the weight of water on top?

[Daphne – It is a lot more difficult, yes. But that isn’t my point here.]

Young Falzon is right, Daphne. The it is more difficult to shift the glass when it is lying at the bottom of the pool because there is a whole column of water pressing down upon it from above, but none from below. Same as trying to lift a card off a table. Once you lift it up an inch, the pressure on the bottom surface will equal the pressure on the top, and then it becomes a question of lifting a heavy object underwater.

But how could the table-top have ended up in the pool, catapulted there by the wind, without breaking? Is there more to this story than meets the eye? Is someone trying to wean Silvio Parnis off old grannies?

[Daphne – Roughly for the same reasons you mention, H.P. Once in the water, it shimmies gently down, cushioned by the water itself. Far more fascinating is MY table-top, which was blown off onto the flagstones (the only pool we have has got terrapins in it) and stayed in one piece. I’m thinking of starting a devotional cult.]

I would think retrieving a glass table-top from a swimming-pool wouldn’t be too much trouble for somebody who rescues pills accidentally dropped by old ladies down the lavatory.

On another note, the physics lesson is flawed – the bit about the glass being heavier because of the weight of water on top of it (basic hydrodynamics). The glass will actually be about 20 to 40% lighter than if it was not under water.

If one tried to pull up the flat lying glass quickly it might break but it has nothing to do with the weight of the water on top of it.