or

When any hot body is cooled, it gives out heat, and its temperature falls. Also, when any cool body is heated, it absorbs heat, and its temperature rises. It has been proved that heat gained or lost is directly proportional to:

  1. mass of the body. (m)
     m
  2. Change in temperature (dt)
     dt

Combining 1 and 2, we get:
            Q  mdt
       or, Q = msdt    where s is constant called specific heat capacity of the body.

Therefore, Q = msdt is the heat equation.