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Re: Everyday Physics questions

Lance wrote:

> Quite a while back we discussed the question of whether a person would
> be more wet by runing (fast movement, but greater impact with drops)
> in rain as opposed to walking (longer duration) in rain. I think the
> discussion was started by an article in the New Scientist. A question
> about everyday physics.
> Now I know that the physicist who studied how best to dunk a donut was
> awarded an ignoble prize, but his work and that of Matthews on the
> buttered side of toast always falling buttered side down did generate
> a lot of public interest, so perhaps it is worth asking another one of
> those everyday physics questions.
> Now to my topic. Fridges in stores tend to be of the chest variety,
> and have no lids. The cold air inside the fridge is heavier than the
> surrounding air and so stays in the fridge keeping the goods cold. But
> an upright fridge with a door contains heavy air that is said to fall
> out everytime you open the door, thus wasting a good deal of power. To
> save electricity people are advised not to open their fridges too
> often.
> If you open a wardrobe or cupboard where goods are tightly packed and
> liable to fall out, you can sometimes stop the goods from falling out
> by opening the door and grabbing what you want very quickly, and then
> slamming it shut again. It takes time for the tightly packed things on
> the shelf to start moving and you can exploit this slowness by acting
> quickly. (Gives you an idea of the state of my jersey drawer, but I'll
> survive the shame).
> Is it possible to open the fridge door and grab your (say) milk bottle
> and then close the door quickly enough to stop the cold air falling
> out? Or, are you simply generating a vacuum when you open the door
> very quickly pulling even more of the cold air out? Perhaps closing
> the door quickly also generates a pressure wave that drives more cold
> air out? Does anyone know the answers or is the whole question
> nonsensical?
> Lance

You would probably be best off having a long plastic glove inside a
transparent fridge; and a hole where you can toss outside the fridge
everything you pick up with the glove.

Roy Schestowitz

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