Wish we'd done Physics now!

[curiosity]

At work today in the nursing office (which is fairly warm) my colleague picked up a 9inch x 4inch sealed tupperware lunchbox that had been used, washed and dried and sitting on the desk for a few hours. Someone had placed a plastic beaker on top of it with a little water in the bottom (the 250ml Ikea coloured type beaker) which the colleague had seen earlier with water in. However when she picked it up the cup was dry and their was a circle shape of moisture drips matching where the cup was on the inside of the box, the outside was dry. Why?? I said I would find out, or try to, I'm relying on you lot! Thank you

[Thicko2006]

Probably magic

[jake-the-peg]

When the tupperware box was sealed the air trapped inside of it will have had water vapour in it too, there's always some humidity in the air.

The beaker was placed on the box containing some water, this evaporated, as it evaporated the beaker cooled, much as sweating cools us.

This means that where the beaker was in contact with the lunchbox the temperature was slightly cooler than elsewhere which caused the water vapour in the box to liquify at that point hence your circle of moisture

[dunr]

The moisture in the lunch box had always moved in australian circles, so,as it condenses it moves up, not down. The water in the beaker would almost certainly have been a viking longboat in disguise. Hope this helped you as much a it did me