Since temperature relates to the thermal energy held by an object or a sample of matter, which is the kinetic energy of the random motion of the particle constituents of matter, an object will have less thermal energy when it is colder and more when it is hotter. If it were possible to cool a system to absolute zero, all motion of the particles in a sample of matter would cease and they would be at complete rest in this classical sense. The object would be described as having zero thermal energy. Microscopically in the description of quantum mechanics, however, matter still has zero-point energy even at absolute zero, because of the uncertainty principle.
Signal "cold" - unofficial (except recommended by CMAS), however used by many schools of diving and propagated through the portals on the diving as one of the useful additional signals.
Goose bumps, a common physiological response to cold, aiming to reduce the loss of body heat in a cold environment.
Cooling refers to the process of becoming cold, or lowering in temperature. This could be accomplished by removing heat from a system, or exposing the system to an environment with a lower temperature.
Air cooling is the process of cooling an object by exposing it to air. This will only work if the air is at a lower temperature than the object, and the process can be enhanced by increasing the surface area or decreasing the mass of the object.
Mercury, despite being close to the Sun, is actually cold during its night, with a temperature of about −170 °C (−275 °F). Mercury is cold during its night because it has no atmosphere to trap in heat from the Sun.
^A cold body is often described as having less heat, although this use of "heat" would be incorrect in the context of physics, as heat refers to the transfer of energy between bodies, which do not "have" heat themselves.