box of water

[EPSBB5]

if you have a box with a funnel on top and a straw at the bottom. you pour in 200 ml and 400 ml comes out. how does this happen?

[jenstar]

There's already 200ml in the box? I guess it would be possible to set it up so that air pressure prevented the original 200ml from coming out, which would be overcome by adding more water. Once it started coming out, it would keep on flowing as in a siphon.

[jake-the-peg]

That's the way I'd do it, take a plastic beaker that can hold 400ml and drill a hole just above the waterline when 200ml is in there. Then put a tube through the hole and down into the bottom of the beaker and pass the other end out of the bottom of the box.

Seal any leaks and add 200 ml of water - when you pour in the additional 200 ml the water is forced out of the tube - when 200 ml is left the last 200 ml is sucked out of the beaker by the syphon effect you have created.

Swirl your cape and bask in the applause.

You could also use a dodgy measure to catch the water that has a mirror dividing it up the centre I guess.  

[Gef]

I think jenstar is correct.