of first law of thermodynamics
first law of thermodynamics explains well the inter convertibility of heat an
work. But it does not indicate the direction of change.
When a hot object is in contact with a cold object, heat always flows from the
hot object to cold object but not in the reverse direction. According to first
law, it is possible for the energy to flow from hot object to cold object or
from cold object to hot object. But in nature the direction of heat flow is
always from higher temperature to lower temperature.
When brakes are applied, a car stops due to friction and the work done against
friction is converted into heat. But this heat is not reconverted to the
kinetic energy of the car.
the first law is not sufficient to explain many of natural phenomena.