If we want to predict whether an object feels hot, burning or cold when we touch it, the real temperature of the body, measured with a thermometer, is definitely important. However, this is not the only important feature of this item.

At least as important is the thermal conductivity of this object, because we perceive heat with our finger only when the finger and the receptors inside it heat up. We only feel cold when the finger gets cold. An object can warm the finger only if the heat moves from the object to the finger; cool only when heat moves from the finger to the object. If the heat transfer is slow, the temperature of the finger does not change much and we perceive the object as warm. If, on the contrary, the heat transfer is fast, then we perceive the object as hot or cold according to its temperature.

The coals used in the experiment shown in the picture are always "burned to the end", i.e. no more heat is generated there from chemical energy. The thermal conductivity of the coal is very poor, so when you step on the coal ... the top layer of the coal cools off, but the foot does not get much warmer. And since thermal conductivity does not add new energy, it is possible to walk on hot coals.

In reality, of course, where the coals touch the soles of the feet, they are no longer hot.

The test set contains bodies made of different materials. The temperatures of the bodies of the experimental set that have been in the classroom for a long time are the same, but it does not feel like this to the touch. To conduct the experiment, we measure the temperatures of these bodies with a thermometer.

Note that if you hold a small body for a long time, it will warm up. Thus, it should be avoided to obtain comparable test results.

You can see the thermal conductivity coefficients of body materials, i.e. the estimation of their heat transfer rate, in the table.