What is Energy?

What is Energy?
Physics defines work as the product of applied force on an object and the distance it moves. If applied force cannot move the object, the work is zero (distance being zero).

   
Work = Force x Distance. 

 
Notice that because work is defined as the multiplicative product of force and distance, knowing just the amount of work doesn't tell you whether you pushed with a little force over a long distance, or a lot of force over a short distance ---  you can accomplish the same amount of work either way. 
The energy of an object, or of a system, is how much work the object or system can do on some other object or system.
In other words, energy measures the capability of an object or system to do work on another system or object.
Consider a ball flying through the air for example. If the ball collides with another ball, the ball will exert a force on the second ball for a moment, which does work on the second ball and causes it to move. The newly acquired kinetic energy of the second ball after the collision is equal to the amount of work exerted on it by the first ball. 

Discuss the various forms of energy.
There are a number of ways in which a system or object can possess energy, i.e. the capability to do work, and each way corresponds to having a different form of energy. 
Kinetic Energy
Kinetic energy is the energy which is associated with the mobility of an object or a system. Consider a baseball flying through the air. The ball is said to have "kinetic energy" for the fact that it is in motion relative to the ground.  

KE = 1 2 mv2
 

Potential Energy
The energy associated with the elevation of an object or a system is called potential energy. Consider a book sitting on a table. The book is said to have "potential energy" because if falls off, it will be accelerated due to the gravity, giving the book kinetic energy. 
PE = mgh   

Thermal, or heat energy 
The collective, microscopic, kinetic and potential energy of the molecules in an object or system (the molecules have kinetic energy because they are moving and vibrating, and they have potential energy due to their mutual attraction for one another. Temperature is really a measure of how much thermal energy something has. The higher the temperature, the faster the molecules are moving around and/or vibrating inside that object or system, i.e. the more kinetic and potential energy the molecules have.  

Chemical Energy
Chemical energy is really a form of microscopic potential energy, which exists because of the electric and magnetic forces of attraction exerted between the different parts of each molecule. These parts get rearranged in chemical reactions, releasing or adding to this potential energy. Consider the ability of your body to do work. The glucose (blood sugar) in your body is said to have "chemical energy" because the glucose releases energy when chemically reacted (combusted) with oxygen. Your muscles use this energy to generate mechanical force and also heat. 

Electrical Energy
All matter is made up of atoms, and atoms are made up of smaller particles, called protons (which have positive charge), neutrons (which have neutral charge), and electrons (which are negatively charged). Electrons orbit around the center, or nucleus, of atoms, just like the moon orbits the earth. The nucleus is made up of neutrons and protons. Charged particles create electric fields that exert force on other charged particles within the field. The electric field applies the force to the charged particle, causing it to move - in other words, do work. Electrical energy is energy that's stored in charged particles within an electric field 

Electrochemical Energy
Consider the energy stored in a battery. Like the example above involving blood sugar, the battery also stores energy in a chemical way. But electricity is also involved, so we say that the battery stores energy "electro-chemically".

Electromagnetic Energy
Consider the energy transmitted to the Earth from the Sun by light (or by any source of light). Light, which is also called "electro-magnetic radiation". Light really can be thought of as oscillating, coupled electric and magnetic fields that travel freely through space.
It turns out that light may also be thought of as little packets of energy called photons (that is, as particles, instead of waves). The word "photon" derives from the word "photo", which means "light".  Photons are created when electrons jump to lower energy levels in atoms, and absorbed when electrons jump to higher levels. 
Each photon also has a specific frequency and wavelength associated with it, which depends on how much energy the photon has. The lower the energy, the longer the wavelength and lower the frequency, and vice versa.  

Sound Energy
Sound waves are compression waves associated with the potential and kinetic energy of air molecules. When an object moves quickly, for example the head of drum, it compresses the air nearby, giving that air potential energy. That air then expands, transforming the potential energy into kinetic energy (moving air). The moving air then pushes on and compresses other air, and so on down the chain.  

Nuclear Energy
The Sun, nuclear reactors, and the interior of the Earth, all  have "nuclear reactions" as the source of their energy, that is, reactions that involve changes in the structure of the nuclei of atoms. In the Sun, hydrogen nuclei fuse (combine) together to make helium nuclei, in a process called fusion, which releases energy. In a nuclear reactor, or in the interior of the Earth, Uranium nuclei split apart, in a process called fission. The energy released by fission and fusion is not just a product of the potential energy released by rearranging the nuclei. In fact, in both cases, fusion or fission, some of the matter making up the nuclei is actually converted into energy. Matter itself is a form of energy. This concept involves one of the most famous formula's in physics, the formula, 

E=mc2 

The energy intrinsically stored in a piece of matter at rest equals its mass times the speed of light squared. 
What should a good source of fuel have? 

i) It should have a high energy output per unit mass or volume. 

ii) It should be easily available. 

iii) It should be easy to store and transport.

iv) It should be economical.  

What are the sources of energy? 

There are two main sources of energy. They are conventional and non-conventional sources of energy. 
i) Conventional sources of energy  Wood, Flowing water and Fossil fuels (coal, petroleum, natural gas).

 ii) Non conventional sources of energy  Solar energy, Wind energy, Biomass energy, Ocean energy (tidal energy, wave energy, ocean thermal energy), Geothermal energy, Nuclear energy etc.  
Some sources of energy are renewable like sun, wind, flowing water, ocean, wood, biomass etc. Some sources of energy are non-renewable like coal, petroleum and natural gas.  

Fossil fuel 

 Fossil fuel is formed inside the earth from the remains of plants and animals after millions of years. The fossil fuels are coal, petroleum and natural gas. Fossil fuels are non-renewable sources of energy so they should be conserved and used judiciously.       

 Disadvantages 

i) Burning of fossil fuels release gases and harmful particles which causes air pollution.

 ii) Burning of fossil fuels release acidic oxides of sulfur and nitrogen which causes acid rain which is harmful for living organisms, affects soil and water, causes damage to buildings, corrosion of metals etc.

 iii) Burning of fossil fuels release a large amount of carbon-DI-oxide gas which increases the temperature of the atmosphere and causes global warming (Green-house effect). 
In thermal power plants the heat energy produced by burning fossil fuels like coal, petroleum or natural gas is used to heat water and change it into steam which rotates the turbines of generators to produce electricity.