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### Course: AP®︎/College Physics 2>Unit 2

Lesson 2: Thermal conduction and heat transfer

# Thermal conductivity of metal and wood

Why metal at room temperature feels cooler than wood at room temperature.

## Want to join the conversation?

• So different materials have different Thermal Conductivity watt/(meter*kelvin). Now if both items are at 70 degrees they will feel different to the touch, metal will feel colder. How could I or calculate to make the two objects feel the same. Like if the wood was 70 degrees and the metal was 80 degrees they would feel the same when touched.
• Actually it's rather easy if you know a little bit of calculus... If you don't know, don't panic, it's also easy... I'm assuming you don't know calculus. So the thing you feel when you touch is actually the rate of heat transfer with respect to time. This means the heat flowing to your body per unit time, say 1 second. So if you can find equal values for rate of heat transfer your question is done.
And to give you a formula I can say that the original formula is like that:
Rate of heat transfer = (Thermal Conductivity*Surface Area*Temperature Difference)/Length
This is called Fourier's LAW or something like that
So back to your question you need to get an equal Rate of Heat Transfer you need to use thermal conductivity of metal and wood and you need to write this equation for both iron and wood and equate them. You will get a ratio of Temperatures.
Sorry for long and ambigious explanation if anything is not clear let me know
• What material has the highest heat conductivity?
• maybe carbon related materials...i think diamond has the highest thermal conductivity.
• If I understand this well, if the metal and the wood were at body temperature, our brain should feel the same for both ?? (in term of temperature)
• its an interesting question...

At room temperature, if you feel the metal of a door handle and the wood of the door, then I would say that the metal would feel colder. (Try it...)
But actually, they must be at the same temperature...why? because they are in thermal contact and therefore same temperature...

The sensor in your body (in your finger tips for example) are measuring the temperature of your skin. why?...because thats where they are: they are in thermal contact with your skin...So: as the heat leaves your skin, the sensor will tell your brain the skin is (getting) colder.

The point here, is that the metal sucks the heat out of your skin faster than the wood does and so the sensors will tell your brain...."metal = cold....wood = warm". But actually, they are the same temperature. Just that metal can draw the heat out of your body faster, so it feels colder to touch.

sooooo, if you, the metal and the wood are all at the same (body) temperature, then, I agree with you... there should be zero heat transfer and, therefore metal and wood would both feel the same temperature. It would make for a very interesting experiment....how might we set it up? :)

OK??
• I'm from China, hope you can understand what I mean. To extend this lecture, I was wondering if it's that objects with different materials have different amount of time to reach equilibrium? And is there a formula to calculate the time elapsed? And is there a coefficient number of different materials of their conductivity?
• Hello Noah,

You have asked a wonderful question.

You could search for “thermal conductivity.” You will find tables listing the conductivity of various materials. For example copper is a excellent conductor of heat. Just for fun examine the construction of fancy cooking pans. You will often find a layer of copper to help distribute the heat allowing a more uniform cooking surface.

You asked about the “temperature vs time.” There is a field of study called “Fourier Series” that describes the heat transfer. The math is very advanced – 2nd or 3rd year college. Know that this Fourier Series is applicable to a wide variety of engineering fields. What started out as a description of heat transfer is also applicable to music and digital signal processing of radio signals.

Regards,

APD
• But what if I keep my hand touched on the wood surface for a long time? Shouldn't it gradually feel as cold as the metal surface after some time?
• No. Why would you expect that? Does the wood's conductivity change?
• Stupid qurstion, but the atoms/molecules of the wood and the metal move all the time or only when I touch the material with my hand?
• Unless the temperature is absolute zero, all atoms are constant motion.
• Clarification:
So the denser the object the better it conducts heat?
• There is a correlation between the density and the specific heat, though it is not so simple, but in many cases the higher the density the higher the specific heat. So it conducts heat more
• Why does metal at feel colder?