Me = Ep + K
where, 'Ep' is the total potential energy, and 'K' is the kinetic energy.
Numerous modern devices convert other forms into mechanical energy and vice-versa, like thermal power plants (heat to Me), electric generators (Me to electricity), turbine (Kinetic energy to Me), etc.
The conservation of mechanical energy is also dependent on whether two bodies experience collision that is either elastic or non-elastic. In the former type, energy is conserved as the original shape and form is regained, whereas in the latter type, deformation of the bodies is permanent, and a different form of energy like heat may emerge from it. In this case, energy may not be conserved but might increase or decrease, depending on the nature of collision and the extent of deformation.
There are various forms of potential energy, depending on the kind of forces involved, such as gravitational potential energy, chemical potential energy, electrical potential energy, magnetic potential energy, and nuclear potential energy. When a force is applied on a body, work is done in a specific direction. This work is represented by taking into account the potential energy of that body, which is denoted by a negative sign, as the energy may increase or decrease depending on whether the work is done against or in the force direction, respectively. This is represented as:
W = -δEp
where, 'W' is work done, and 'δEp' is the potential energy present in the body.
K = (M × V2) ÷ 2 ----- equation 3
where, 'K' is the total kinetic energy, 'M' is mass of the body, and 'V' is the velocity at which it is traveling. For a rotating body, the kinetic energy is represented as:
K = (I × W2) ÷ 2
where, 'I' and 'W' are the moment of inertia and angular velocity of the body.
Kinetic energy varies according to the frame of reference of an observer, along with inertia. For example, if a car passes an observer who is stationary, then the speeds of both objects are relative to each other, and hence the car possesses kinetic energy with a positive value. But, if both the observer and car are traveling at the same speed, then this energy is equivalent to zero.
K = (M × V2) ÷ 2 ----- from equation 3
Thus, if a gas has 'N' molecules, then its thermal energy can be represented as.
U = (N × M × V2) ÷ 2
= (N × kT) ÷ 2
where, 'k' is the Boltzmann constant, and 'T' is the measured temperature or the heat of the body.
From the above formula, it is clear that this energy operates by the processes of absorption or emission of heat, during its transfer from one portion of the system to another.
Often, the terms 'electromagnetic energy' or 'electromagnetism' are used, as electricity and magnetism can exist in combined form in the form of waves. In case of this type, the strength of the field depends on several factors such as magnetic dipole moment, strength of the current produced, amount of magnetic material present, etc. A common example that incorporates the use of this energy is that of the electromagnet. This device is utilized in our everyday lives, and it consists mainly of a wire coiled around a metallic material. When an electric current is passed through the wire, a magnetic field is formed, which can be further used for different purposes depending on its strength and the associated magnetic forces.
The motive force that powers the human body is provided by the chemical energy that is derived through the process of respiration, which involves the formation and breaking of inter-atomic molecular bonds. Through molecular rearrangements, along with compound formation and breakdown, the biological world derives energy. For example, the formation of glucose from the process of photosynthesis is useful for energy generation in a plant cell.
This type of energy is often represented in the form of the Rydberg constant, which is given as:
R∞ = (Me × E4) ÷ 8e02H3C
= 1.097 × 107 × m-1
'Me' is the mass at zero motion, 'E' is the charge, 'eo' is the space permittivity, 'H' is the Planck constant, and 'C' is the light speed.
When sound energy is released from an object, the waves spread in all directions, and are a combination of both potential and kinetic energy densities of the body. For example, if a car passes an observer, the first kind of energy that is experienced by the person consists of the sound waves, and their strength depends on several parameters like wave frequency and amplitude, distance between the observer and the vehicle, the total area of the surroundings, etc.
Light energy or power is measured mainly by a unit called radiant flux. There have been several theories that attempt to explain the propagation of light waves through any medium including space. The most famous one is the Quantum theory, which states that light travels in the form of small packets of particles called quanta, and each quantum shows dual personality, i.e., it can behave as a wave as well as a particle. Light energy is often accompanied with other kinds like heat, sound, chemical, and magnetic. It can be said that this energy is a secondary form and exists only when another type undergoes transformation due to several processes. These might include chemical reactions, nuclear fission and fusion processes, absorption, reflection, refraction, etc.
G = (g × M1 × M2) ÷ R2
where, 'G' is the gravitational attraction, 'g' is the gravitational constant, R is the distance between the two objects, and 'M1' and 'M2' are the masses of both the bodies, respectively.
Gravitational energy is the weakest one of all in our Universe, but the force caused by it could be very strong in some celestial objects like black holes, wherein it is theorized that the gravitational forces would be so strong that not even light can escape from its attraction. On our planet, this energy helps to keep us stable and balanced. The heavier the body in terms of mass, the higher would be its gravitational attraction. Hence, as the Sun contributes the maximum mass of our solar system, its high gravity makes it possible the revolution of every planet around it.
Nuclear power has several applications in the modern world, and since several decades, this energy is utilized to produce electricity and heat supplies. Entire ships and submarines can be operated on the basis of a nuclear source. Some nations also use this energy form to make nuclear weapons. The electricity production is done with the help of a nuclear reactor and radioactive material. The atomic nuclei are bombarded with electrons, which cause them to split and form daughter elements. The energy released is used to power generators, which further produce electric power.
For example, when a spring is extended, the stored potential energy makes it possible for the stretching of the material, and when the extensional forces are removed, it reverts back to its original position. Another example is the one, which was described earlier in this article―the bow and arrow description. In this instance, the bow string is stretched till a particular point, and after the arrow is released, it reverts back to its original position due to the elastic energy that is present during its stretching.
After a certain point, elasticity might get converted to plasticity, wherein the object gets permanently deformed. This happens because each material has its own limit of elasticity, and beyond this limit, the elastic forces stop operating. This can be easily observed with the Young's modulus experiment.
dW = γ × dSa
where 'dW' is the work done and represents total surface energy of the body, 'γ' is surface tension, and 'Sa' is the surface area of the body.
In solid objects, surface energy is usually present in combination with elastic energy. When a solid is stretched this energy is mostly measured in the form of heat. The volume of the deformed body remains more or less same, as compared to the original object. Contact angles are also measured in order to determine this type of energy.