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Thermal energy
 
 
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Thermal energy is a form of energy that manifests itself as an increase of temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
. It is also the sum of sensible heat
Sensible heat

Sensible heat is potential energy in the form of thermal energy or heat. The thermal body must have a temperature higher than its surroundings ....
 and latent heat
Latent heat

In thermochemistry, latent heat is the amount of energy in the form of heat released or absorbed by a chemical substance during a change of state of matter , or a phase transition....
.

e f refers to the degrees of freedom, T refers to the temperature, and k to Boltzmann's constant. For example, a monatomic particle in an ideal gas has three degrees of freedom, and thus,

The total thermal energy is the sum of the thermal energies of all particles in the system.






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Thermal energy is a form of energy that manifests itself as an increase of temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
. It is also the sum of sensible heat
Sensible heat

Sensible heat is potential energy in the form of thermal energy or heat. The thermal body must have a temperature higher than its surroundings ....
 and latent heat
Latent heat

In thermochemistry, latent heat is the amount of energy in the form of heat released or absorbed by a chemical substance during a change of state of matter , or a phase transition....
.

Definitions


The thermal energy of a single particle in a thermal bath is:

where f refers to the degrees of freedom, T refers to the temperature, and k to Boltzmann's constant. For example, a monatomic particle in an ideal gas has three degrees of freedom, and thus,

The total thermal energy is the sum of the thermal energies of all particles in the system. Thus, for a system of N particles,

Note that Uthermal is rarely the total energy of a system; for instance, there can be static energy that doesn't change with temperature, such as potential energy
Potential energy

Potential energy can be thought of as energy stored within a physical system. It is called potential energy because it has the potential to be converted into other forms of energy, such as kinetic energy, and to do Mechanical work in the process....
, bond energy
Bond energy

In chemistry, bond energy is a measure of bond strength in a chemical bond. For example the carbon-hydrogen bond energy in methane E is the enthalpy change involved with breaking up one molecule of methane into a carbon atom and 4 hydrogen Radical s divided by 4....
 or rest energy (E=mc2).

History of the term


The term was first used explicitly by James Prescott Joule, who studied the relationship between heat, work, and temperature. He observed that if he did mechanical work on a fluid such as water, by agitating the fluid, its temperature increased. He proposed that the mechanical work he was doing on the system was converted to "thermal energy." Specifically, he found that 4200 joules of energy were needed to raise the temperature of a kilogram of water by one degree Celsius!

Thermal energy in an ideal gas


Thermal energy is most easily defined in the context of an ideal gas
Ideal gas

The ideal gas model is a model of matter in which the molecules are treated as non-interacting point particles which are engaged in a random motion that obeys conservation of energy....
. In a monatomic
Monatomic

In physics and chemistry, monatomic is a combination of the words "mono" and "atomic," and means "single atom." It is usually applied to gases: a monatomic gas is one in which atoms are not bound to each other....
 ideal gas
Ideal gas

The ideal gas model is a model of matter in which the molecules are treated as non-interacting point particles which are engaged in a random motion that obeys conservation of energy....
, the thermal energy is exactly given by the kinetic energy of the constituent particles.

Other definitions


Thermal energy per particle is also called the average translational kinetic energy possessed by free particles given by equipartition of energy.

Thermal energy is the difference between the internal energy
Internal energy

In thermodynamics, the internal energy of a thermodynamic system, or a physical body with well-defined dimension, denoted by U, or sometimes E, is the total of the kinetic energy due to the motion of molecules and the potential energy associated with the vibrational and electricity energy of atoms within molecules or crysta...
 of an object and the amount that it would have at absolute zero
Absolute zero

Absolute zero is a temperature marked by a 0 entropy configuration. It is the coldest temperature theoretically possible, and cannot be reached, by artificial or natural means....
. It includes the quantity of kinetic energy
Kinetic energy

The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the mechanical work needed to accelerate a body of a given mass from rest to its current velocity....
 due to the motion of the internal particles of an object, and is increased by heating
Heating

Heating may refer to:*HVAC: Heating, ventilation and air-conditioningHeating devices, or systems:*Block heater, or headbolt heater, an electric heater that heats the engine of a car to ease starting in cold weather...
 and reduced by cooling
Cooling

Cooling is the Heat transfer of thermal energy via thermal radiation, heat conduction or convection. It may also refer to:...
.

See also

  • Enthalpy
    Enthalpy

    In thermodynamics and chemistry, the enthalpy is a quotient or description of thermodynamic potential of a system, which can be used to calculate the heat transfer during a quasistatic process taking place in a closed system thermodynamic system under constant pressure....
  • Entropy
    Entropy

    In many branches of science, entropy is a measure of the disorder of a system. The concept of entropy is particularly notable as it is applied across physics, information theory and mathematics....
  • Heat transfer
    Heat transfer

    Heat transfer is the transition of thermal energy or simply heat from a hotter object to a cooler object . When an object or fluid is at a different temperature than its thermodynamic system or another object, transfer of thermal energy, also known as heat transfer, or heat exchange, occurs in such a way that the body and the surround...
  • Radiation
    Radiation

    In physics, radiation describes any process in which energy emitted by one body travels through a medium or through space, ultimately to be absorbed by another body....
  • Thermal efficiency
    Thermal efficiency

    In thermodynamics, the thermal efficiency is a Dimensionless quantity performance measure of a thermal device such as an internal combustion engine, a boiler, or a furnace, for example....
  • Thermal science
    Thermal science

    Thermal science is the combined study of thermodynamics, fluid mechanics, and heat transfer. This umbrella-subject is typically designed for non-engineering students and functions to provide a general introduction to each of three core heat-related subjects....