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Amanshu*
Giggity Giggity goo
Wed 28th Jan '09 3:50PM
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Can anyone think of a short idiom including the word 'future'? i.e. something akin, but completely different to 'making history' or 'saving time' or even 'blue skies'. It's been bugging me for a while because I'm sure there must be something
   

Agentgonzo
There's no pee in catheter!
Thu 29th Jan '09 10:11AM
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Amanshu was bold enough to comment:
Can anyone think of a short idiom including the word 'future'? i.e. something akin, but completely different to 'making history' or 'saving time' or even 'blue skies'. It's been bugging me for a while because I'm sure there must be something



Future-proof?
  

Epicure_mammon
I'm not crazy cause I take the RIGHT pills :)
Thu 29th Jan '09 2:13PM
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Yesterday is history, tomorrow is the future, Today is a gift, that's why they call it the present
  

Agentgonzo
There's no pee in catheter!
Thu 12th Feb '09 11:39PM
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Do Turkeys float?
  

Spanners*
Misses his big brother :(
Fri 13th Feb '09 9:20AM
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Why do you never see a vindaloo on a curry menu these days?
    

General*
Windows Bob - the best!
Fri 13th Feb '09 1:09PM
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Spanners was bold enough to comment:
Why do you never see a vindaloo on a curry menu these days?



I've seen them.
    

Swoop*
CHIMPO
Sat 21st Feb '09 7:20PM
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Amanshu was bold enough to comment:
Can anyone think of a short idiom including the word 'future'? i.e. something akin, but completely different to 'making history' or 'saving time' or even 'blue skies'. It's been bugging me for a while because I'm sure there must be something



The future is another country?

Or too long?
 

Spanners*
Misses his big brother :(
Wed 11th Mar '09 2:41PM
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When I'm sat in the steam room at my gym and I blow on my skin, it makes my skin feel vastly hotter - like the temperature has shot up 20 degrees. Why is this?
    

Agentgonzo
There's no pee in catheter!
Wed 11th Mar '09 4:55PM
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Spanners was bold enough to comment:
When I'm sat in the steam room at my gym and I blow on my skin, it makes my skin feel vastly hotter - like the temperature has shot up 20 degrees. Why is this?



There are two ways that your skin can change temperature.
1) Radiation of heat to/from your skin (like feeling the heat of a hot fire in front of you) - we can ignore this one here
2) conduction of the heat to/from your skin and the surrounding atmosphere. This is felt when you mash a waffle-iron to your face or plunge your delicates into a tub of icy water. This is what we consider here.

When you sit in a room that is hot/cold, you can feel the temperature of the surrounding air on your skin by as your skin conducts heat to/from the surrounding air. Lets assume you're ina hot room (because a cold steam room would just be unpleasant). After a second or two, if you are not moving, your skin cools down a thin layer of the surrounding air (as your skin warms up and you feel the warmth) just around you. This thin layer is cooler than the rest of the steam room and so you don't feel the full warmth of the steam room around you.

when you blow yourself (pauses for childish giggling) you push warmer air from the surrounding room onto your skin in place of the thin insulating layer and the heat from this 'new' air can be conducted into your skin at a faster rate than the heat from the cooler air. This is why you feel hot (giggles to self again).

It's exactly the same process as Wind Chill
  

Spanners*
Misses his big brother :(
Sat 14th Mar '09 7:33PM
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Aha, again a great conundrum solved by AG!
That also explains to me why it's the combination of sweat and wind that cools you down - the sweat warms and humidifies the air next to your skin and the wind carries it away. Nice.
    

Swoop*
CHIMPO
Tue 17th Mar '09 12:11PM
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Spanners was bold enough to comment:
When I'm sat in the steam room at my gym and I blow on my skin, it makes my skin feel vastly hotter - like the temperature has shot up 20 degrees. Why is this?



It's either exactly as Agent Gonzo described above, OR...

have you considered the possibility that you're a dragon? That would explain both the increase in temperature when you blow on your skin and also the prediliction for sitting in a steam room.

Perhaps you should run a few tests?
 

Agentgonzo
There's no pee in catheter!
Tue 17th Mar '09 12:32PM
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Spanners was bold enough to comment:
That also explains to me why it's the combination of sweat and wind that cools you down - the sweat warms and humidifies the air next to your skin and the wind carries it away. Nice.


Partially, but there is also something else going on here. Evaporation (state change from liquid to gas) is an endothermic process. Think of it this way. Temperature can be thought of as the vibrational energy of the individual molecules. Because of the stochastic (random) way molecules of the liquid are distributed, all molecules will not have exactly the same vibrational energy (temperature) as eachother at a specific time. The temperature of the liquid as a whole is average energy of the specific molecules. As there are such a massive number of molecules in a drop of sweat, this temperature of the liquid as a whole does not fluctuate over time, even though the energy of individual molecules does (as they bounce off eachother etc).

Now, liquids are liquids because the molecules do not (individually) have enough energy to overcome their mutual attractive forces and so remain bound (attracted to) eachother. If they gain enough energy, they can bounce free of the attractive forces of the rest of the molecules and float free (turn into a gas). This energy is provided (normally) by heat, which is why you have to raise the temperature of a liquid to turn it into gaseous form (boiling it).

Whilst you can turn a whole pot of water into gas by heating it, you can also (slowly) turn the liquid to gas by just leaving it there (evaporation). What happens here is that as the molecules of the water interact with eachother, bouncing off eachother and whatnot, they exchange energy (vibrations) with eachother, so the energy of each individual molecule is constantly changing. If, upon one of these interactions, the molecule receives enough energy from its brethren to escape their attractive forces, it flees the liquid as a gaseous molecule. As more and more of these molecules flee, the amount of molecules left decreases - the water is evaporating.

Now, lets look at this in more detail. As the molecules bounce off eachother and exchange energy between themselves, the total energy must remain constant (conservation of energy). That means that as a molecule gets more energy from its brethren to escape, the energy of its brethren must (on average) decrease. That means that the temperature of the remaining water (average energy of all molecules) must decrease. Think of it this way. You're at a crowded taxi rank with a load of strangers, all with different amounts of money. A taxi turns up and takes only the two richest people in his cab and drives off. The average amount of money of all the people at the rank has now just gone down because the two richest have buggered off. Therefore, as molecules evaporate, the temperature of the liquid will decrease slightly.

This can be seen in a GCSE physics experiment where you get a beaker of ether (volatile liquid) and blow air through it. As the ether evaporates, it cools so much that condensation and then frost appear on the outside of the beaker.

And there you have it. THe same things is happening with the sweat on your skin. The water evaporates in the wind and cools the remaining sweat and your skin in the process (as well as through conduction that you mentioned above)

Thermodynamics is complicated.
  

General*
Windows Bob - the best!
Tue 17th Mar '09 2:18PM
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7th Apr '03
I heartily recomend getting a copy of "Six Easy Pieces" by Richard Feynman which explains this process in a way which is really easy to understand along with most of the basics of physics pre Einstein.
    

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