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The second law of thermodynamics (or law of increased entropy) defines/states that every spontaneous process always leads to an increase in the entropy (S) of the universe. In simple terms, the law states that the entropy of an isolated system will never decrease over time.
The Second Law clearly states that it is impossible to convert thermal energy into mechanical energy with 100 percent efficiency. Example, when we look at the piston in an engine, we see that the gas is heated to increase its pressure and drive a piston. But even when the piston moves, there is always some heat left in the gas that cannot be used for any other work. The heat is lost and must be disposed of. In this case, this is done by transferring it to a heat sink. or in the case of a car engine, waste heat is removed by venting the spent fuel-air mixture to the atmosphere. In addition, the usually unusable frictional heat must also be dissipated from the system.
Second law of thermodynamics is a very important topic for students as it is always asked in the exams. In this article we will learn about the Second law of thermodynamics, what the Second law of thermodynamics defines, the Second law of thermodynamics statement and more.
Entropy
Entropy is defined as a measure of the randomness of a system or the measure of energy. Entropy is also considered as a quantitative index which defines the quality of energy.
Statements of Second law of Thermodynamics
The second law of thermodynamics can be expressed in different ways, the most important classical statements are the statement of Rudolf Claus (1854), the statement of Lord Kelvin (1851) and the statement in the axiomatic thermodynamics of Constantin Carathody in 1909.
Kelvin – Planck statement
It is not possible to change all the heat which is extracted from a hot body into work. In the heat engine, the working substance absorbs heat from the hot body, then converts part of it into work and gives the rest off to the cold body. There is no engine available which can convert all the heat absorbed from the source into work without losing heat to the sink. This means that a sink is required to get continuous work.
Clausius Statement
It is not possible to build a device that works in a cycle that can transfer heat from a colder body to a warmer body without consuming work. Also, energy does not flow spontaneously from a low temperature object to a higher temperature object. Here it is required to note that we are referring to the net transfer of energy. The transfer of energy from a cold object to a hot object can occur through the transfer of energetic particles or electromagnetic radiation. However, in every spontaneous process there is a net transfer from the hot object to the cold object. And some form of work is required to transfer the net energy to the hot object. In other words, if the compressor is not powered/driven by an external source, the refrigerator cannot run. The heat pump and the refrigerator work on the basis of Clausius’ statement.
Both the Clausius and Kelvin statements are equivalent, that is a device that violates the Clausius statement also violates the Kelvin statement and vice versa.
In addition to these two statements, a French physicist Nicolas Léonard Sadi Carnot called “Father of Thermodynamics”, gives the second law of thermodynamics.
Carnot Cycle
According to history, the origin of the second law of thermodynamics lies solely in Carnot’s principle. The law relates to a cycle of a Carnot heat engine which is notionally operated in the extremely slow limit mode known as quasi-static, such that the work and heat are only transferred between subsystems that are always in their own internal states of thermodynamic equilibrium. The Carnot engine is an idealized device which is of particular/special interest to engineers concerned with the efficiency of heat engines. Carnot’s principle was recognized by Carnot at a time when the caloric theory of heat was being seriously considered, before the first law of thermodynamics was accepted and before the concept of entropy was expressed mathematically. It physically corresponds to the second law of thermodynamics and is still valid today.
Conclusion
The second law of thermodynamics restricts the direction of heat transfer and the achievable efficiencies of heat engines. The first law of thermodynamics states that the energy of the universe remains constant, although energy can be exchanged between the system and the environment but not created or destroyed. The second law of thermodynamics ( or law of increased entropy) defines/states that every spontaneous process always leads to an increase in the entropy (S) of the universe. In this article we learn about Second law of thermodynamics, what Second law of thermodynamics defines, Second law of thermodynamics statement and more.
Example
Brakes applied by bus driver suddenly
On a bus trip, when the bus driver suddenly presses the brake, we tend to feel a momentary push forward. The reason for this feeling by passengers sitting inside the bus is because of the law of inertia. Due to the inertia of motion, our body continues to maintain a state of motion even after the bus has stopped, thus pushing us forward.
Newton’s Second Law of Motion
Sir Isaac Newton’s First Law of Motion states, A frame at relaxation will continue to be at relaxation, and a frame in movement will be in movement until it’s far acted upon via any outer or external force. Then, what occurs to a frame while an outside force is carried out to it? That scenario is defined by Newton’s Second Law of Motion. According to NASA, this regulation states, Force is identical to the change in momentum in line with change in time. For a regular mass, force equals mass into acceleration. In mathematical form it is written as F = ma, where F equals force, m is mass of object and a is acceleration of object. The math at the back of that is pretty simple. If you double the force, you double the acceleration, however in case you double the mass, you narrow the acceleration in half. Because the acceleration is directly, and mass is inversely proportional.
Formula
According to Newton’s Second laws of motion
F = ma
Where, F = force, m = mass of the object, a = acceleration
Example
Hitting of a ball
A ball develops a certain acceleration after being hitted. The acceleration with which the ball moves is directly proportional to the force acting on it. This means the harder you will hit the ball, the faster it will move, proving Newton’s second law in everyday life.
Newton’s Third Law of Motion
According to Newton, whenever objects A and B interact, they exert force on each other. When you sit in the chair, your body exerts a downward force on the chair, and the chair exerts an upward force on your body. Here are two forces resulting from this interaction: a force on the chair and a force on your body. These two forces are called action force and reaction force and are the subject of Newton’s third law of motion. Basically it stated by Newton’s third law is: for every action, there is an equal and opposite reaction. The statement means that in every interaction there is a pair of forces acting on the two interacting objects. The size of the forces on the first object is equal to the size of the force on the second object. And the direction of the force on the first object is opposite to the direction of the force on the second object. Forces always occur in pairs of equal and opposite reaction-action forces.
Example
Stretching an elastic band
When someone pulls an elastic band, it returns to its authentic position automatically after leaving it. The more distance you pull it, it exerts the extra force. This is identical while you pull or compress a spring respectively. This pull action is stored as energy and is released as a reaction with the same and opposite force.
Conclusion
Newton’s give three important laws of motion that become the root of classical mechanics, it explains every aspect related to rest and motion of any object. Moreover it explains about the force acting on the object and it also explains that every object exerts forces on each other when they are in contact.
