# What Is Temperature? Definition in Science

In science, temperature is a measure of hotness or coldness, which in turn is a measure of the kinetic energy of particles. In equations, the capital letter T usually represents temperature. It is an intensive property of matter, as it does not depend on the number of particles in a sample and can be written in an equation as a ratio of extensive properties.

• Temperature is a measure of the “hotness” of an object or material.
• It reflects the kinetic energy of particles of matter.
• Heat flows from a body with higher temperature to one of lower temperature.

### Temperature Units

A thermometer is an instrument that measures temperature. Temperature scales like Celsius and Fahrenheit are relative temperature scales, with zero points relating to the freezing point of water. Celsius (°C) and Fahrenheit (°F) values use degrees. The Kelvin scale measures absolute temperature, where zero is absolute zero. Kelvin temperature (K) does not have degrees.

There are different types of thermometers, but the liquid thermometer is common. Here, a liquid in a tube either expands or contracts according to changes in temperature, causing it to rise or fall relative to a numerical scale. Calibrating a thermometer gives accurate temperature readings.

### Difference Between Temperature and Heat

Temperature (T) and heat (Q) are closely related, but not the same. Heat is the transfer of kinetic energy from one body to another, which in turn changes their temperature. An object has a temperature, but it does not have “heat.” The energy transfer, measured in units such as joules, always goes in the direction from the body with higher temperature to the one with lower temperature.

### How Temperature Works

Matter consisting of particles with high kinetic energy has a high temperature. When atoms, ions, and molecules have a lot of kinetic energy, they vibrate and move and interact more often with each other and their container (for fluids). The friction from particles brushing against each other generates heat. Sometimes this energy lets a material melt or vaporize or participate in chemical reactions.

When the temperature drops, particles have less energy. They can pack more closely together, so gases condense into liquids and liquids becomes solids. Temperature changes also affect other properties, such as pressure, electrical conductivity, and hardness.

But, atoms and molecules still have some kinetic energy even at absolute zero. At absolute zero, that energy is at its minimum value.

### References

• Moran, M.J.; Shapiro, H.N. (2006). Fundamentals of Engineering Thermodynamics (5th ed.). John Wiley & Sons. ISBN 978-0-470-03037-0.
• Swendsen, Robert (2006). “Statistical mechanics of colloids and Boltzmann’s definition of entropy”. American Journal of Physics. 74 (3): 187–190. doi:10.1119/1.2174962
• Thomson, W. (Lord Kelvin) (March 1851). “On the Dynamical Theory of Heat, with numerical results deduced from Mr Joule’s equivalent of a Thermal Unit, and M. Regnault’s Observations on Steam”. Transactions of the Royal Society of Edinburgh. XX (part II): 261–268, 289–298.
• Quinn, T.J. (1983). Temperature. London: Academic Press. ISBN 0-12-569680-9.