Thermal Conductivity: If you Want a Good Thermometer, Don’t Use Your Body


Martin Sagendorfby: Martin Sagendorf

An Easy Question:  Which is warmer – which is cooler?

In the strictest sense, it’s a matter of energy.  And we use temperature as a measure of energy level.  As we all know, the greater the energy level, the higher the temperature… But, although this is absolutely true; sometimes it’s not exactly what we perceive in everyday life.  When asked, we all can testify that when we touch a piece of metal we’ll say it feels cold.  But is it really cold?  Is it or isn’t it ‘cold’?

The Answer Is…

… very simple.  If the piece of metal is at room (ambient) temperature it cannot be ‘cold’ – it must be at the same temperature as the temperature of the room.

But First:

Let’s discuss ‘perceived temperature’: this is what we ‘think’ the temperature is.  It isn’t always the actual temperature (of the object we touch).  Thus we enter a wonderful combination of both physics and biology.  Physics describes the absolutes.  Biology describes the biological reactions (interpretations) of our physical world.

It’s a matter of thermal conductivity and our nerves.  Some materials are good conductors of heat (energy) and some are not.  Our nerves sense only temperature – so if thermal energy is rapidly removed from the tissues surrounding our nerve endings (like at our finger tips), our nerves sense that the temperature ‘they feel’ is cooler – e.g. the material is removing thermal energy from the body tissue surrounding the nerve ends at a rate faster than our body can re-supply energy to the tissues – thus our nerves sense this as ‘cooler’.

Now:

A truly illustrative and memorable way to present the question: Read the rest of this entry »