Temperature – What is it…really?

Image Courtesy NASA

Most people, including many engineers, have to think a little about the meaning of temperature. Clearly it’s related to heat, but it’s not heat.


Temperature: A measure proportional to the average translational kinetic energy associated with the disordered microscopic motion of atoms and molecules. The flow of heat is from a high temperature region toward a lower temperature region.

-Courtesy of the references cited below but mostly based on the operational definition on the HyperPhysics pages at Georgia State University by R. Nave. and the discussion in “Traceable Temperatures” Second Ed. by Nicholas and White. See the discussions and definitions below for my understanding.

Looking at textbooks and related references and even websites for a definition of temperature can be very frustrating. Many talk around the subject and never get to the point or never state a clear definition.

Oh, yes, we can find information about the fact that temperature is not heat and what temperature scales are. We know it’s related to heat and there is a difference between them.

What is it? It’s got to be on the Web…..

Bottom line. It is. However it is like finding the needle in a haystack; just like many topics on the web.

Search engines do not help much; it takes digging by someone who understands the subject.

A serious group of experts at The American Society for Testing and Materials (ASTM International) publishes standards about devices and information on how to calibrate, test and specify temperature sensors. But their standard on Terminology, ASTM E-344, is notably missing a definition for “Temperature”!


Is it just us, or have you, too, noticed that there seems to be a real difficulty in defining or agreeing the meaning of the word and concept of “Temperature”.

(Bottom line: It is not a simple concept, despite all the work done on it over the past few hundred years. Yes, it can be defined, but not easily.

In many cases simplified explanations, not true definitions, are used.

See the HyperPhysics Web site at Georgia State University (U.S.A.) for the clearest and best explained definition we have seen to date. Their definition appears at the bottom of this page.)

More Resources

About Temperature
This document was prepared for the middle school math teachers who are taking part in Project Skymath. It is also hoped that the general public will find it interesting.
Search domaineo.ucar.edu/skymath/tmp2-html

What is Temperature?
Temperature is a measure of the average heat or thermal energy of the particles in a substance. Since it is an average measurement, it does not depend on the number of particles in an object.
Search domain coolcosmos.ipac.caltech.edu/cosmic_classroom/light_lessons/thermal/temperature.html

Temperature – HyperPhysics Concepts
Increasing temperature will increase molecular speed. An object with less massive molecules will have higher molecular speed at the same temperature. When kinetic temperature applies, two objects with the same average translational kinetic energy will have the same temperature. Internal or …
Search domain http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/temper.html#c1

Heat and temperature (article) | Khan Academy
Temperature is a measure of the average kinetic energy of the atoms or molecules in the system. The zeroth law of thermodynamics says that no heat is transferred between two objects in thermal equilibrium; therefore, they are the same temperature. Heat is sometimes called a process quantity, because …
Search domain https://www.khanacademy.org/science/chemistry/thermodynamics-chemistry/internal-energy-sal/a/heat

Visit https://mrpyrometer.com/static-pages/ to see all the related measurement pages and more.