# What is this called?

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Back in grade school, I remember learning about some property substances have that requires a certain amount of kinetic energy to increase that object's temperature by a certain number of degrees.

For example, a tire iron that's been baking in the sun all day will probably be too hot to pick up with your bear hands. However, an object that has rubber or wood as a handle (such as a shovel) can still be picked up, even though it's been absorbing just as much sunlight as the tire iron. This is because iron has a much smaller _____________________ than wood does: It takes a less kinetic energy to increase iron's temperature than wood.

What is this property called? Can someone fill in the blank for me, and also provide me the equation for how I can calculate this quality?

Heat capacity?

Specific heat?

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Sounds like specific heat capacity: http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/heatingandcooling/buildingsrev3.shtml

There is another factor involved in how hot or cold things feel, and that is the conductivity: how quickly they take the heat away from your hand. So a piece of wood or plastic will feel warmer, on a cold day, than a piece of metal at the same temperature. Just because the plastic warms up where you touch it (because the heat can't flow away) while the metal will feel cold (because you would have to heat the whole thing for it to feel warm).

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I will start from the beginning, because the answer is not simple.

Something feels hot to touch because heat is transferred from it to the hand.

Heat only flows from a higher temperature to a lower temperature.

The greater the temperature difference, the greater the rate of heat transfer.

Your sense of touch is mostly sensitive the the rate of heat transfer, not the absolute temperature difference.

If you touch a plastic spoon and a metal one at the same higher temperature than your hand the metal one will feel warmer, because the rate of transfer is greater.

The reason for this is because the heat in the spoons has two separate sections to its journey into your hand.

Firstly some heat has to be transferred from the point of contact to your hand.

This increases the hand temperature at the contact and depresses the spoon temperature there.

Then heat has to be internally transferred within the spoon from the now hotter parts to the point of contact before more can be transferred to your hand.

This happens quickly in a metal (or other conductor) spoon but slowly in a plastic (other insulator) one.

The speed of replenishment is controlled by the thermal conductivity of the spoon material.

Your garden spade is more complicated because the heat capacity (specific heat) of the wood is about 5 times that of iron (about 2.5 to 0.5 in metric units) so the iron blade will heat up to a higher temperature than the wood for a given solar input.

So the wood starts off at a lower temperature than the iron and transfers heat more slowly.

Both effects combine to make the wood appear (and be) cooler.

Since you asked for the property which is smaller for iron I assume you are looking for the heat capacity.

The conductivity of iron is much larger than that of wood.

Edited by studiot
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In addition, a thermometer would tell that iron gets hotter in sunlight than wood or plastic. The heat emissivity makes a difference, though in our atmosphere, it's not the most important.

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