Temperature
Overview

Temperature is a physical property
Physical property
A physical property is any property that is measurable whose value describes a physical system's state. The changes in the physical properties of a system can be used to describe its transformations ....

of matter that quantitatively expresses the common notions of hot
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

and cold
Cold
Cold describes the condition of low temperature.Cold may also refer to:*Common cold, a contagious viral infectious disease of the upper respiratory system*Chronic obstructive pulmonary disease...

. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot. Heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

spontaneously flows from bodies of a higher temperature to bodies of lower temperature, and no net heat will be exchanged between bodies of the same temperature. Such bodies are said to be in "thermal equilibrium
Thermal equilibrium
Thermal equilibrium is a theoretical physical concept, used especially in theoretical texts, that means that all temperatures of interest are unchanging in time and uniform in space...

".

The temperature of a substance varies with the microscopic speed of the fundamental particles that it contains, raised to the second power; that is, it is proportional to the mean kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

of its particles.