ENERGIES CLASS NOTES FOR Mechanical engineering





Thermodynamics change one form

of energy into another form. There

are number of thermodynamic

devices to achieve the objective.

There are various forms of energy.

These are required in different devices.


Energy is the capacity to do work. It units are kJ.
It is of two types.
1. Stored Energy—It is the energy possessed by a system within its boundaries.
Examples of stored energy
a. Potential energy
b. Kinetic energy
c. Internal energy
d. Chemical energy
e. Nuclear energy

    2. Transit Energy—It is the energy which crosses the boundaries of the system
Examples of transit energy
a. Heat energy
b. Work energy
c. Electrical energy
Law of Conservation of Energy
Sum of various energies of a system remains constant. One form of energy can change into another form. Energy can neither be created nor be destroyed. This law is also called First Law of Thermodynamics.
Sources of Energy
Solar Energy
Fuel Energy
Wind Energy
Nuclear Energy
Geothermal Energy
Water Energy
Ocean Tidal Energy
Ocean Waves Energy


It is internal Energy of the molecules. This is invisible. It is the sum of potential and kinetic energy of the molecules. This is affected by the change of temperature only.
Mathematically it is given by
du = 1 x cv dt kJ/kg  (specific)
dU m x c v dt  kJ    (total)

Difference between Work and Internal Energy

Sr. No.


Internal Energy

Transit energy
Stored Energy
Path function
Point function
Do not depend on the state of the substance
Depends on the state of the substance
It can be fully converted into heat
It cannot be fully converted into work
 Work is a function of pressure, temperature and volume.
 It depends only on temperature and it is always under constant volume.
 There are different equations for a flow process and a non-flow process respectively. It also depends on the type of process i.e. Iso-thermal, iso-baric, isentropic or poly-tropic.
For a non flow process W = ∫ p dV
For a non-flow process W = ∫ — V dp
 There is one equation for internal energy i.e.
U =  m C v (t1 — t2) kJ