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Equations for Temperature Limits

by Ron Kurtus (revised 11 November 2014)

The lower and upper temperature limits can be approached but not physically reached. There is a relationship between kinetic energy, speed of the particles and temperature. Absolute zero is the coldest possible temperature. The limit for the highest temperature is when the particles reach the speed of light.

Questions you may have include:

This lesson will answer those questions. Useful tool: Units Conversion


There are equations that determine the relationship between kinetic energy of an ideal gas, temperature and velocity of the atoms or molecules in the gas.

Note: An ideal gas is a theoretical gas composed of randomly-moving point particles that interact only through elastic collisions. It is useful in determining simple equations, as opposed to the highly complex ones of the real world.

Kinetic energy and temperature

The relationship between the kinetic energy of the molecules or atoms in an ideal gas and temperature is:

KE = 2kT/3


Kinetic energy-temperature relationship equations for real-world gases, liquids and solids are too complex to work with at this level of study.

Kinetic energy and velocity

The kinetic energy of a moving mass of particles is:

KE = ½mv²


Temperature and velocity

You can find the relationship between the temperature and the velocity of the particles in an ideal gas.

Since KE = 2kT/3 and KE = ½mv², you can substitute for KE to get 2kT/3 = ½mv². Then, you can multiply by 3 and divide by 2k to get:

T = 3mv²/4k


Absolute zero

It can easily be seen from T = 3mv²/4k that when T = 0 kelvin, the velocity of the particles v = 0. Thus the kinetic energy due to linear movement is zero. But the atoms still possess spin, which means they still have some energy.

Another fact is that the equation is really an approximation, since we are dealing with an ideal gas. A real-world gas would not be able to reach T = 0.

Temperature and the speed of light limit

The greatest temperature possible is limited by how fast its atoms can travel. The upper limit that anything can travel is at the speed of light.

Although kinetic energy is KE = ½mv², the limiting energy is defined by Einstein's Theory of Relativity equation

E = mc²


Thus, in theory, the highest possible temperature is defined by:

T = 3mc²/2k

You can calculate that temperature by substituting the appropriate values. This equation may not fit into the Theory of Relativity, since the mass of a particle increases dramatically as the particle approaches the speed of light. But, at the very least, it is an interesting exercise.


The lower and upper temperature limits can be approached but not physically reached. The relationship between kinetic energy, speed of the particles and temperature determines that value of absolute zero and the limit for the highest possible temperature.

Surpass your limitations

Resources and references

Ron Kurtus' Credentials


Kinetic Temperature - HyperPhysics

Physics Resources


Top-rated books on Physics of Temperature

Top-rated books on Absolute Zero

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