Naked Science Forum
General Science => General Science => Topic started by: neilep on 13/11/2007 17:02:37
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Dearest Peeps Of International Plastic Wrapping Fun & Luff,
See this bowl of yummy veggies ?
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Nice isn't it ?..Notice how veggy like and ready to be zapped by microwave hugs they are ?
But, when ewe heat it.....heat expands yes ?....the clingfilm expands to create a dome......so why does the clingfilm get sucked in onto the vegetable AFTER the cooking is done ?..surely it should continue to expand or maintain it's dome like structure eh ?
I've sent an email via a Medium to Sir Christopher Wren ( he's an authority on domes)...but I got an 'out of office' reply !!
Can ewe help me ?
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Loadsa pressure when the water inside's boiling.
This forces some steam and air out past the film / bowl gap.
When it cools, the steam condenses and the pressure is lower - atmospheric pressure pushes in and, because it is pushing inwards on the (by now soft) film, forms a better seal than before and keeps the pressure inside, low. Hence the dome.
They always tell you to put a tiny hole in the film to stop the vacuum-pak effect.
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Loadsa pressure when the water inside's boiling.
This forces some steam and air out past the film / bowl gap.
When it cools, the steam condenses and the pressure is lower - atmospheric pressure pushes in and, because it is pushing inwards on the (by now soft) film, forms a better seal than before and keeps the pressure inside, low. Hence the dome.
They always tell you to put a tiny hole in the film to stop the vacuum-pak effect.
THAN YOU THANK YOU THANK YOU very much !!....I understand !!
YAYYYYYYYYYYYYYYY !!