Energy Conservation Theorem

Sadi Carnot, in 1824, published a book named “Reflections on the motive power of fire”, in which he illustrated the first principle of thermodynamics. Later after further studies, it came to be known as the second law of thermodynamics. In 1845 James Prescott Joules conducted various experiments giving the three laws of thermodynamics.

There are four laws of thermodynamics- zeroth law, first law, second law and the third law. Thermodynamics is the branch of physics dealing with energy and its various forms.

Basic terminology

Surroundings: Anything that is not a part of a system but can interact with it is termed as the surrounding of the system.

Open system: A system that can exchange both mass and energy with its surroundings is an open system.

Closed system: A system that can only exchange energy with its surroundings, but the exchange of mass is prohibited called a closed system.

Isolated system: A system that is not capable enough to exchange neither mass nor energy with its surroundings is called an isolated system.

Isothermal process: Process having a constant temperature.

Isobaric process: Process having  constant pressure.

Isochoric process: Process having constant volume

Zeroth law of thermodynamics

The Zeroth law of thermodynamics takes temperature as its fundamental concept. It explains the relation between systems having the same temperatures.

It states that if one system is in thermal equilibrium with another system and a third system exists which has the same temperature, then all these systems are in thermal equilibrium with one another.

The first law of thermodynamics

It is also termed the law of Conservation of energy states that energy in a system is constant. It can neither be created nor destroyed but can change forms. 

In a closed system, the internal energy is constant, which is equal to the energy being supplied to the system and the work being done by the system on its surroundings.

The second law of thermodynamics

This law talks in terms of entropy. The entropy of the universe tends to increase and can never decrease.

The third law of thermodynamics

The third law of thermodynamics also talks in terms of entropy. It states that at a temperature that is absolute zero, the entropy of a system will be zero too.

Types of Energy Conservation

1. When a body falls freely due to gravity, mechanical energy of the body remains conserved. The total energy in any body is the sum of its kinetic energy and its potential energy. This sum remains constant while the body falls. At point A mass= m, u=0; Considering total height=h then AB=k and BC=h-k;
   At A P.E.= mgh
   K.E.=1/2mu2=0 [because u=0]
   Total energy=P.E. + K.E.
                       = mgh+0
                       =0
   At B velocity of the body is v1
   P.E.=mg(h-k)
   K.E.=1/2mv12
           [v12=0+2gk because v12=u2+2gk]
         =1/2m*2gk
         =mgk
   Total energy= P.E. + K.E.
                       =mgh-mgk+mgk
                     =mgh
   Similarly, at point C
   h=0 therefore P.E.=0
   K.E.= 1/2m*2gh
         =mgh
   Total Energy=mgh
   Thus at any point, the total energy of the body is conserved. It doesn’t change with time. This proves that the energy of a system is conserved and can only change forms.

2. Another example of energy conservation is seen in a simple pendulum. At rest, it has maximum kinetic energy, and at mean positions, it has maximum potential energy because of gaining a certain height. 

3. Another example of energy observation is nuclear reactions. There are infinite reactions that keep on happening like that in the sun, but the total energy of a system is always reserved. 

4. When an object is hooked in spring and then left, the elastic potential energy of that spring changes into the kinetic energy of the body.

5. In day to day life, this law can be witnessed by the use of solar panels. These solar panels transform the sun’s energy into different forms like electricity. 

Conclusion

Energy Conservation is a law that states that the entire universe’s energy is constant. Both energy and mass are fundamental quantities that man can not create, nor can they be destroyed. In an isolated system, say the universe, mass and energy are constant and will remain so forever.