Familiar sensations of hotness and coldness are described with adjectives such as hot, warm, cold, cool etc. So, the quantity that indicates how warm or
cold an object is called TEMPERATURE. However you must note here that these physical sensations of warmth and cold are not reliable because
they depends on contrast as explained in this observation.
Suppose if we place our right hand in hot water and left hand in cold water, if after a few minutes we place both the hands in water at room temperature then
you will notice that to the right-hand water will appear to be cold and to left-hand, water will appear to be hot.
From the above observation we can conclude that assessing the temperature of a body by mere sense of touch or comparing the degree of hotness of a body with
respect to another body does not help in measuring the temperature quantitatively and accurately.
Another observation about hot and cold bodies in contact is that, when they both are in contact, the temperature of cold body increases and that of the hot
body decreases. This happens because energy is transferred from hot body to cold body when they are in contact and this is a non-mechanical process.
This energy which is transferred from one body to another without any Mechanical Work involved is known as HEAT. Heat is a form of energy
and heat transfer from one body to another takes place by virtue of temperature difference only. Also heat transfer takes place from the body at higher
temperature to a body at a lower temperature. So, we can also say that Heat is energy in transit. On microscopic level heat energy possessed by a body
is due to the kinetic energy of the molecules that makes up the body.
Heat energy can change from one form to another. S.I. unit of heat is Joule (J) and SI unit of temperature is Kelvin (K).
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