What is Energy?
In Physics, energy is defined as a scalar quantity which denotes the amount of work that can be done by a force under certain constraints. Energy transforms from one into many forms, but if you make a sum of all this amount of energy transformed in different forms, the sum total remains constant. This is the law of conservation of energy. The sum of the total amount of energy in a system isolated from interactions, remains constant. The universe as a whole is a closed system, and therefore, the total amount of energy in the universe remains constant. In every isolated system, since the total energy remains constant, energy can only change form. That is, neither is energy created, nor is it destroyed. It only changes form.
Out of the different forms of energy, the one addition which may surprise you is matter itself! Matter and energy are inter-convertible. This has been established by Albert Einstein, through his theory of relativity. The celebrated equation 'E = mc2' provides a means for calculating the amount of energy created from matter. Just as matter can be converted into energy, even energy can be converted back to matter in phenomena like pair production, where particle - antiparticle pairs are created from pure energy. So, matter is a form of energy.
Energy transformations occur in such a way that entropy always increases. Entropy is the number of ways in which a system could exist. It could be defined as a measure of disorder. So, energy transformations always occur in such a way that disorder always increases! Left alone, an isolated system tends to transform into a system with maximum entropy or disorder. A system tries to attain a state of minimum energy and maximum multiplicity.
What are the Different Manifestations of Energy?
How many types of energy are there? There are as many forms of energy as the number of energy transformations. Every kind of change that happens in the universe is an energy transformation. Energy may be classified in a variety of ways. It could be classified according to the different energy sources or according to the force that causes the energy change. Let us get acquainted with the different forms of energy that we encounter in our day-to-day life:
- Potential Energy & Kinetic Energy: Potential energy is the energy a particle or an object possesses on account of its position in a conservative force field, while kinetic energy is the energy which a particle possesses due to its motion. All forms of energy can basically be classified into potential energy, kinetic energy, or a mixture of both.
- Gravitational Energy: Gravitational energy is the energy possessed by an object according to its position in the gravitational field.
- Electromagnetic Energy: It is the energy transmitted through electromagnetic waves. Electrostatic energy is the energy possessed by a charge configuration, due to the imbalance of charge. Electrical energy is a form of electromagnetic energy.
- Sound Energy: It is the energy transported by sound waves, which are longitudinal disturbances traveling in a material medium.
- Nuclear Energy: It is the energy contained within an atomic nucleus.
- Wind Energy: It is the mechanical energy derived from wind motion.
- Chemical Energy: Chemical energy is the energy derived from various chemical reactions. This includes the exothermic combustion of gasoline that drives the car engine.
- Thermal Energy: Thermal energy or heat energy is energy derived from vigorous atomic or molecular motion.
- Solar Energy: It is the heat radiated by the Sun in the form of electromagnetic waves, which can be converted into electrical energy through solar cells. The solar energy drives the whole ecosystem on Earth. It is a type of renewable energy.