Cold

For the infectious disease, see Common cold. For other uses, see Cold (disambiguation).

An iceberg, which is commonly associated with cold
Signal "cold" – unofficial (except recommended by CMAS), it is nonetheless used by many schools of diving and propagated through diving websites as one of the more useful additional signals[1]
Goose bumps, a common physiological response to cold, aiming to reduce the loss of body heat in a cold environment
A photograph of the snow surface at Dome C Station, Antarctica. A part of the notoriously cold Polar Plateau, it is representative of the majority of the continent's surface.

Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjective perception. A lower bound to temperature is absolute zero, defined as 0.00 K on the Kelvin scale, an absolute thermodynamic temperature scale. This corresponds to −273.15 °C on the Celsius scale, −459.67 °F on the Fahrenheit scale, and 0.00 °R on the Rankine scale.

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 the classical sense. The object could 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.

  1. ^ Scuba Diving – Hand Signals Archived 14 April 2009 at the Wayback Machine