Freezing burn

Can a bar be both cold and hot at the same time?

Grasp the outermost bars and hold on to them for a minimum of ten seconds. Now grasp the centremost bar with both hands.

The room-temperature bar in the middle feels hot to one hand and cold to the other.

While you were holding onto the outermost bars, the cold and heat sensitive receptors in your palms adapted to their different temperatures. The room-temperature bar then felt different to each hand, because of the way that the receptors reacted to the change in temperature; for one hand the change was cooling and for the other, warming.

The receptors on the surface of the skin that are sensitive to heat only produce impulses at temperatures of 35–45°C. As the heat increases, the heat-sensitive pain receptors begin to work at the same time as the tissue begins to be damaged.

The receptors that are sensitive to cold temperatures react at temperatures between 15–35°C. They are also activated if the temperature rises above 45°C. Contact with an extremely hot stimulus may produce a so-called paradoxical cold sensation.

Both heat-sensitive and cold-sensitive receptors adapt within a few seconds in the same manner as most sensory cells. This is seen, for example, in the way that our skin adapts to the feel of a hot bath or a cold pool.