There are many ways of looking energy. One way is to go back to the root word. Energy is derived from the words ‘En’ and ‘Ergon’: meaning ‘in’ and ‘work’. Thus, energy is something that has work in it. Also ‘energos’ means ‘activity.
Different Dimensions Of Energy
Energy Characterizes Life And Non-life
- Energy is also one basis upon which life and non-life are characterised.
- The ability to make an ‘effort’ differentiates life and non-life.
- To make an effort, life requires energy. Thus, life is something that utilizes energy to do some work.
- In other words, energy is expended to do work. The rate at which the energy is expended is called ‘power’.
Energy As The Capacity To Do Work
- Another way of looking at energy is the state of orderliness and disorderliness in nature.
- Those things in nature, which have in them unused energy, are in a state of orderliness. Eg: Fuels which are energy stores are in a state of orderliness.
- Those things in nature that do not have unused energy are in a state of disorderliness. Eg: Heat that is released upon burning of fuel is in a state of disorderliness.
- Fancy names for orderliness and disorderliness are negentropy and entropy respectively.
- If left to itself orderliness in nature always decays into a state of disorderliness. (2nd law of thermodynamics)
- However, in the journey of moving from orderliness to disorderliness, we can extract some orderliness. This is what energy is and can be used to do work. That is why energy is the capacity to do work.
- Illustration: burning a fuel(orderliness) gives heat (disorderliness). A part of this heat (disorderliness) can be converted to mechanical motion of the turbine(orderliness). Note there is a limit to which you can reverse the process of orderliness changing to disorderliness. This is called the efficiency of any system.
- Thus, Sun is a store of orderliness, plants through photosynthesis take a part of this orderliness and store in the chemicals it makes (primarily carbon, hydrogen and oxygen). Animals use the energy store of plants to do some work and store some for later use. In all these systems major part of orderliness is lost. (plants can take only 0.5% of sunlight(orderliness) and store it in chemicals(starch) and animals can use only a part of this and so on)
- In short, the amount of usable ‘energy’ goes on reducing from Sunlightà Photosynthesis à Plants à Animals.
- Further plants and animals when buried under earth’s crust for millions of years become fossil fuels which are simply stores of energy that was stored in them long ago.
- These stores of energy can be used to do some work which is what we do when we burn coal or petrol.