Short Answer:
The law of conservation of energy states that energy can neither be created nor destroyed, but it can be transformed from one form to another. The total amount of energy in a closed system always remains constant.
In simple words, energy may change its form, such as from mechanical to electrical or heat energy, but the total energy before and after the transformation remains the same. For example, in an electric motor, electrical energy is converted into mechanical energy, but the total energy is conserved.
Detailed Explanation:
Law of Conservation of Energy
The law of conservation of energy is one of the most fundamental and universal laws in physics and engineering. It states that in any isolated or closed system, the total energy always remains constant even though energy may change its form. This means energy can be transformed from one form to another or transferred between objects, but it can never be created from nothing or completely destroyed.
This principle helps explain how mechanical, electrical, thermal, chemical, and other forms of energy are interrelated and interchangeable. It is used in all branches of engineering and science, especially in mechanics, thermodynamics, electrical engineering, and machine design.
Definition
The law of conservation of energy can be defined as:
“Energy can neither be created nor destroyed, but it can only be converted from one form to another. The total energy of an isolated system remains constant.”
Mathematically,
or,
In an ideal system (without losses),
This shows that even when energy appears to vanish (as in friction or heat), it is actually converted into another form, ensuring that the total energy remains the same.
Explanation of the Law
When a system performs work or transfers heat, energy is not lost but converted into different forms. For instance:
- When you lift a weight, mechanical work converts into potential energy.
- When the weight falls, potential energy is converted into kinetic energy.
- When the object hits the ground, kinetic energy transforms into sound and heat energy.
In every stage, the total energy before and after remains equal. Hence, the law of conservation of energy ensures that energy transformation always follows a balance — no energy disappears; it simply changes its form.
Different Forms of Energy
Energy exists in many forms, and according to this law, one form can be converted into another:
- Mechanical Energy:
It is the energy possessed by a body due to its motion (kinetic energy) or position (potential energy).
Example: Water falling from a dam converts potential energy into kinetic energy. - Electrical Energy:
Produced by the movement of electric charges in a conductor.
Example: Electric motors convert electrical energy into mechanical energy. - Thermal Energy (Heat):
Energy due to the motion of particles in a substance.
Example: Friction converts mechanical energy into heat. - Chemical Energy:
Energy stored in chemical bonds.
Example: Burning of fuel converts chemical energy into heat and mechanical work in engines. - Nuclear Energy:
Energy stored in atomic nuclei.
Example: Nuclear reactions convert nuclear energy into heat and radiation energy. - Light Energy:
Energy in the form of electromagnetic radiation.
Example: Solar panels convert light energy into electrical energy.
According to the conservation law, these forms of energy can be transformed from one type to another, but the total quantity of energy remains unchanged.
Illustration of Energy Conservation
Let’s consider some simple examples that show how energy is conserved:
- Pendulum:
- When a pendulum swings, its energy continuously changes between potential and kinetic forms.
- At the topmost position, it has maximum potential energy and zero kinetic energy.
- At the bottommost position, it has maximum kinetic energy and zero potential energy.
- The total energy throughout the motion remains constant.
- Hydroelectric Power Plant:
- Water stored in a dam has potential energy due to its height.
- As water flows down, its potential energy converts into kinetic energy.
- The moving water turns turbines, converting kinetic energy into mechanical energy.
- The turbine drives a generator, producing electrical energy.
- In every step, total energy remains constant—only the form changes.
- Electric Motor:
- Converts electrical energy into mechanical energy.
- Due to losses (like heat and sound), not all electrical energy becomes mechanical, but the total energy (useful output + losses) remains equal to the input.
- Combustion Engine:
- Converts chemical energy of fuel into thermal energy (by burning).
- Thermal energy converts into mechanical energy to move pistons.
- Some energy is lost as heat and sound, but the total energy remains the same.
Mathematical Expression
The law can be represented mathematically as:
For a mechanical system:
Where,
- = Potential Energy =
- = Kinetic Energy =
Thus,
This means that when potential energy decreases (object falls), kinetic energy increases equally, keeping the total energy constant.
Applications in Engineering
- Design of Machines:
Engineers use the law to analyze energy input and output in engines, turbines, pumps, and machines. - Thermodynamics:
Used in the First Law of Thermodynamics, which states that the heat supplied to a system equals the sum of the work done and the change in internal energy. - Power Plants:
Helps in converting chemical or nuclear energy into electrical energy efficiently. - Structural Engineering:
Used to calculate strain energy stored in structures due to loads. - Energy Efficiency:
Applied in determining the performance of systems and minimizing energy losses.
Relation with First Law of Thermodynamics
The First Law of Thermodynamics is based on the law of conservation of energy and can be stated as:
“The heat supplied to a system is equal to the sum of the work done by the system and the change in its internal energy.”
Mathematically,
Where,
- = Heat added to the system,
- = Work done by the system,
- = Change in internal energy.
This shows that energy is never lost but only transformed between heat, work, and internal energy.
Importance of the Law
- Ensures that energy transformations in nature and machines follow predictable patterns.
- Helps engineers design energy-efficient systems.
- Provides the foundation for energy conservation and renewable energy technologies.
- Helps in analyzing losses in systems like engines, turbines, and power plants.
- Establishes the fundamental relationship between work, heat, and energy.
Conclusion
The law of conservation of energy is a universal principle stating that energy cannot be created or destroyed but can only change its form. It ensures that the total energy in a closed system always remains constant. This law forms the foundation of all branches of science and engineering, especially mechanical and thermal systems. By understanding and applying this principle, engineers can design efficient machines, predict energy transformations, and minimize energy losses in real-world applications.