That's because metal conducts heat much better than wood does. Since your hand is hotter than room temperature, both the metal and the wood conduct heat away from it. Since the metal conducts better, that cools your hand faster, and that's what you feel .
By the same token, if the metal and the wood are hotter than your hand, the metal will feel hotter than the wood and our answer revolves around the fact how fast heat to and from your body can be transfered with a specific material in contact.
Note that what we feel by touch of skin is not the temperature it is the rate of heat transferred to or from skin contact area.
Firewalking is the act of walking barefoot over a bed of hot embers or stones.
Firewalking has been practiced by many people and cultures in all parts of the world, with the earliest known reference dating back to Iron Age India – c. 1200 BC. It is often used as a rite of passage as a test of an individual's strength and courage, or in religion as a test of one's faith.
Here is a clip from movie Housefull, where Akshay Kumar is walking on coal bed to impress his lover, who must not be as impressed after reading this article.
Study of Heat and Mass Transfer has explained the phenomenon, concluding that the amount of time the foot is in contact with the ground is not enough to induce a burn, combined with the fact that embers are not good conductors of heat.
When two bodies of different temperatures meet, the hotter body will cool off, and the cooler body will heat up, until they are separated or until they meet at a temperature in between. What that temperature is, and how quickly it is reached, depends on the thermodynamic properties of the two bodies. The important properties are temperature, density, specific heat and thermal conductivity.
In heat transfer analysis,thermal diffusivity is the thermal conductivity divided by density and specific heat , and tells how much heat energy the body absorbs or releases in a certain amount of time per unit area when its surface is at a certain temperature.
Since the heat taken in by the cooler body must be the same as the heat given by the hotter one, the surface temperature must lie closer to the temperature of the body with the greater thermal diffusivity. The bodies in question here are human feet (which mainly consist of water) and burning coals(product of poor heat conductor wood).
most fire-walks occur on coals that measure about 1,000 °F (538 °C),and recorded upto 1,800 °F (980 °C) coals in some cases.
Now question arises, Can a man(say Akshay Kumar) sustainable to walk on embers at this temperature could also perform it on metallic platform maintained at same temperature? Here is how it will look like
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