Heat is a form of energy. Heat is caused by the movement of atoms, molecules or other particles in matter. Things like fire, the sun, and boiling water are all very hot.

Properties of Heat

Heat is a form of energy and not a substance contained in an object.

Heat can move from one place to another in different ways:

Measuring Heat

Heat can be measured. That is, the amount of heat a thing has can be given a number. The heat measurement numbers only mean something if there is also a unit of measurement. One of the units of measurement for heat is the Joule.

nternal energy

In thermodynamics, the internal energy of a thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes E, is the total of the kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the potential energy associated with the vibrational and electric energy of atoms within molecules or crystals. It includes the energy in all the chemical bonds, and the energy of the free, conduction electrons in metals.

The internal energy is a thermodynamic potential and for a closed thermodynamic system held at constant entropy, it will be minimized.

One can also calculate the internal energy of electromagnetic or blackbody radiation. It is a state function of a system, an extensive quantity. The SI unit of energy is the joule although other historical, conventional units are still in use, such as the (small and large) calorie for heat.

Absolute zero

In physics, absolute zero is the temperature where the particles of matter stop moving. Absolute zero is impossible to achieve, because all particles move, even if it's just a small vibration. There are many people who have gotten very close to absolute zero, but the record temperature was 450 PK (Picokelvin).

The Kelvin and Rankine temperature scales are defined so that absolute zero is 0 kelvins (K) or 0 degrees Rankine (°R). The Celsius and Fahrenheit scales are defined so that absolute zero is −273.15 °C or −459.67 °F.

At this stage the pressure of the particles is zero. If we plot a graph to it, we can see that the temperature of the particles is zero. The temperature cannot decrease any further. The closer the temperature of an object gets to absolute zero, the less resistive the material is to electricity therefore it will conduct electricity better.

First law of thermodynamics

The first law of thermodynamics says that heat transfer is a form of energy transfer and that energy does not vanish (law of conservation of energy).

The most common wording of the first law of thermodynamics is:

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The increase in the internal energy of a thermodynamic system is equal to the amount of heat energy added to the system minus the work done by the system on the surroundings.

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