Too good to be true?

[Sysman]

Everywhere is downhill.

Shouldn't that be in one of the many house prices threads?

[Bob Dalek]

Okay Diver before I let Archimedes rest in peace. Recent thoughts/investigations.

After looking at a dozen or so articles on the web I can see no reference to applications where the bottom surface of an object is removed from the equation (and therefore where Archimedes principle no longer holds). I assume you accept that Archimedes principle *is* due to pressure differentials acting on the top and bottom surfaces rather than because 'it just happens'

Here are some thoughts on experiments where we might make the pressure differential different to what you'd experience in everyday situations.

- An object is sealed to the bottom of a tank of water to prevent water (specifically its pressure) from getting underneath it and creating a net buoyant force. A seal preventing water from getting underneath will have to resist water pressure at that depth though, so this seal would need to be strong enough to resist as much sideways force as the buoyant upward force being eliminated, so without further thought I'm not sure how useful a test this would be.

- Eliminate the underside pressure on an object by making a hole in the bottom of a water filled tank and putting something ordinarily buoyant (less dense than water) in the hole. I imagine an ordinarily buoyant stopper would now not float, but instead would remain stuck in the hole. Or if the stopper is less wide than the hole, would flow out of the hole at the same speed as the water rather than rise.

- A sucker. A ordinary sucker works because when it's pressed against a surface, air is driven out leaving lower pressure air behind in the sucker. The now greater pressure of the atmosphere surrounding the sucker keeps it stuck to a surface. The same principle can be extended to water (I think - I tried it with a sink plug in a water-filled sink). This sink sucker worked underwater, without any air being in the sucker.

It's unsatisfactory that much is written about pressure differentials proving Archimedes correct, where it's applicable, but seemingly so little in situations where the pressure differentials are not as they occur in hum-drum cases :tantrum

You are my old physics teacher and I claim my crisp £5.