<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Temperature is a physical quantity expressing hot and cold . Temperature is measured with a thermometer, historically calibrated in various temperature scales and units of measurement . The most commonly used scales are the Celsius scale, denoted in ° C (informally, degrees centigrade), the Fahrenheit scale (° F), and the Kelvin scale . The kelvin (K) is the unit of temperature in the International System of Units (SI), in which temperature is one of the seven fundamental base quantities . </P> <P> The coldest theoretical temperature is absolute zero, at which the thermal motion of all fundamental particles in matter reaches a minimum . Although classically described as motionless, particles still possess a finite zero - point energy in the quantum mechanical description . Absolute zero is denoted as 0 K on the Kelvin scale, − 273.15 ° C on the Celsius scale, and − 459.67 ° F on the Fahrenheit scale . </P> <P> Temperature is a proportional measure of the average translational kinetic energy of the random motions of the constituent microscopic particles in a system (such as electrons, atoms, and molecules); based on the historical development of the kinetic theory of gases, but more rigorous definitions include all quantum states of matter . </P>

The temperature at which molecular energy is at a minimum