What is heat?



In summer you drink cold water daily, in contrast, in winter you drink hot coffee. Why in hot you drink cold liquid and in cold you drink hot?

The answer is heat and Its transfer.When you drink cold water you transfer heat from your body to the liquid, similarly when you drink coffee, you transfer heat from liquid to body.

But what is the heat?


First we define heat in 3 ways and then explain it.

Definition#1 "the transfer of energy between two or more objects because of temperature difference between them" 



Definition#2"the total translation kinetic energy of the molecules of a substance is called heat"




Definition#3"Heat is thermal energy in transit" 



Explanation: Unit the middle of 19th century many scientists believed that heat was an actual a substance called caloric which means invisible but later it was discovered that heat is not a substance, but transfer of energy between two or more objects.

Heat is related to Translational Kinetic energy of the molecules of a substance of random molecular motion. Molecules of a substance may also vibrate and rotate, having vibrational kinetic energy and rotational kinetic energy respectively, but these energy do not play any role in heat and do not define it.
The most precise and important definition of heat is that "it is thermal energy in transit".It is important to point out that matter does not contain heat .It was discovered by Rumford in his cannon-boring experiment.Rumford realized that matter contains molecular Kinetic and potential energy but not heat.It is wrong to say that "the body contain 2J heat". It is molecular way transferring energy.Heat is similar to Work.A body does not contain work .It does work or work has done on it.

Symbol:

It is denotes by Capital letter Q.

Units:The SI unit of Heat is Joule and Conventional or Biological unit is Calorie.

Joule:One joule is defined as 

"the amount of energy required to displace a body or particle through a distance of 1m, by a force of 1newton".

Calorie:"The amount of heat required to raise the temperature of 1kg of  water by 1 degree Celsius at 1atm pressure". 


Relation between Joule and Calorie 

1calorie=4.184Joules 


Important point:Colorie is larger unit than than Joule because 1 calorie is equal to 4.184 joules