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Author Topic: Why are materials such as some metals always colder than room temperature?  (Read 2747 times)

thedoc

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Why are materials such as some metals always colder than room temperature?
« on: 13/05/2015 16:50:02 »
de Waal Davis asked the Naked Scientists:

Why are materials such as stainless steel, porcelain, etc always colder than room temperature?

What do you think?
« Last Edit: 13/05/2015 16:50:02 by _system »

chiralSPO

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Re: Why are materials such as some metals always colder than room temperature?
« Reply #1 on: 13/05/2015 18:58:29 »
This is an illusion!

Our bodies don't measure temperature directly, but instead rely on how quickly heat flows. In general, this is a good approximation: it will easily tell you whether an object is warmer or cooler than (surface) body temperature, and a very hot object will transfer heat to your hand more quickly than a moderately warm object will, so you can also gauge how different from body temp the object is.

However, there is a wrinkle: Let's say there are two objects that are exactly the same temperature, slightly colder than body temperature. The object that can accept heat fastest will appear to be colder than the other one.

Metals and porcelain are good conductors of heat (especially compared to air), so they will feel colder than the surrounding air (assuming this is colder than body temperature--On a hot day metal objects will appear to be hotter than the air.)

wolfekeeper

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Re: Why are materials such as some metals always colder than room temperature?
« Reply #2 on: 23/08/2015 01:55:23 »
I've been trying to explain this to my mother.

She uses a porcelain sink to 'keep things cool'.

I know, I know.

I tried to explain it's the same temperature as everywhere else- I even put a thermometer in the sink, but she looks at me with a mixture of blankness and 'I KNOW it's colder'.

She doesn't use it for anything important or perishable though; only meat.

Let this posting be my epitaph.

Other things she doesn't get includes why it's a bad idea to open the windows of the house when it's hotter outside than it is inside the house (ironically it often is due to the concrete floors acting as a thermal reservoir but the porcelain sink doesn't mass enough for that to work).

PmbPhy

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Re: Why are materials such as some metals always colder than room temperature?
« Reply #3 on: 26/09/2015 03:52:05 »
This is an illusion!

Our bodies don't measure temperature directly, but instead rely on how quickly heat flows. In general, this is a good approximation: it will easily tell you whether an object is warmer or cooler than (surface) body temperature, and a very hot object will transfer heat to your hand more quickly than a moderately warm object will, so you can also gauge how different from body temp the object is.

However, there is a wrinkle: Let's say there are two objects that are exactly the same temperature, slightly colder than body temperature. The object that can accept heat fastest will appear to be colder than the other one.

Metals and porcelain are good conductors of heat (especially compared to air), so they will feel colder than the surrounding air (assuming this is colder than body temperature--On a hot day metal objects will appear to be hotter than the air.)
My compliments on a very good explanation.

Pecos_Bill

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Re: Why are materials such as some metals always colder than room temperature?
« Reply #4 on: 26/09/2015 05:49:03 »
Perhaps i can help with a klein, bissel, wenig Gedankenexperiment, Nicht wahr?

Imagine that it is 60 degrees with a 10 mph wind and you are mother naked under a suit of chain mail. ( The thermal conductivity of 1% carbon steel is 43) Do you feel cold?

Now you take off the chain mail and dress yourself in wool trousers and a nice thick wool sweater.  ( The thermal conductivity of wool is 0.07) Do you still feel cold?

Don't try this at home kids. You could catch your death.

The Naked Scientists Forum

Re: Why are materials such as some metals always colder than room temperature?
« Reply #4 on: 26/09/2015 05:49:03 »