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# Energy

The greatest gift of nature to our universe is a energy. It is a boon to the mankind and it exists in different forms like solar, wind, hydro, earthly and sky. In Hindu philosophy these are considered as five giants. The greatest and most tapped form is the energy from sun.

But then, why there is a hue and cry for energy and why there is a crisis of energy. It is mainly because of two reasons. The first is that the energy when converted for doing a work cannot be cycled back. Secondly, we still lag behind in tapping up all the energy resources though considerable advancement is made. To achieve this, we must clearly understand what is energy?

## What is Energy?

Let us approach to the concept of energy from our daily experience. A man can walk a certain distance under normal condition. The same person may not be able to do the same if he is sick. What makes the difference in the two situations? That is ‘energy’. When in normal health, he has the ‘energy’ to walk and in the second case he does not have that ‘energy’. Thus,

Energy is basically defined as an ability to do some act or work.
This above Energy Definition is same not only for a man but extends to all kinds of living things, non living things and even to natural objects. For example, a horse has an energy to drag a cart, a piece of coal has the energy to produce heat and a storm has the energy even to uproot a tree.

Since the energy is described as an ability to do a work, the accepted general unit of energy is ‘joules’. However, the units of energy vary depending on the context.

It may be realized that energy is an hidden ability which varies from case to case. Further, energy does not pertain only to a particular type of act. A man’s walk corresponds to one type of energy and burning of coal corresponds to another type. Therefore, energy can be of various and different types. Let us take a closer look in the next section.

## Types of Energy

As mentioned earlier energy is a hidden ability which varies from case to case. The ability is ‘hidden’ or stored in many ways and means, giving rise to different types of energy.

An energy which is stored by virtue of its position is called ‘potential energy’. Suppose an object of mass ‘m’ is carried to a height ‘h’, the work done to do that is m $\times$ g $\times$ h. This is stored in the object as a ‘Potential Energy’ at that height.

An energy which is acquired when an object is in motion, then the type of energy acquired is called as ‘Kinetic Energy’. For a linear motion of an object of mass ’m’ moving at a velocity of ‘ v ’, the kinetic energy is $\frac{1}{2}mv^{2}$.

The energy stored or released under a thermal change is called ‘Thermal Energy’.

The most common type of energy that we come across in our daily life is Electrical Energy in which electricity is stored and this electricity is used for various purposes.

The energy stored or released under a chemical change is called ‘Chemical Energy’.

The energy associated with atomic structure of a material is called ‘Atomic Energy’.

Like this we can list various types of energy depending on the context.

Energy resources mean the sources which has the energy. In true sense every object in the world is acquired with some energy. But in practical sense, we refer energy resources for the agencies which have substantial energies that can be transformed for useful purposes.

## Conservation of Energy

An interesting feature of energy is the conservation of energy. That is, in a closed system, the total energy remains the same. In other words, an energy can not be created or destroyed. It can only be transferred from one form to another form.
The change in energy of an object due to a transformation is equal to the work done on the object or by the object for that transformation.

For example, when an object is at a height, a potential energy is stored by virtue of its height. When the same object is dropped the height decreases. But because of the reduction in height, the potential energy is not destructed but it is only transformed into kinetic energy as visible from its velocity during the fall.
Conservation of energy helps us a lot in energy solutions. We are able to predict the results whenever an energy is transformed to another form.

## Energy Resources

Energy resources mean the sources which have the energy. In true sense every object in the world is acquired with some energy. But in practical sense, we refer energy resources for the agencies which have substantial energies that can be transformed for useful purposes.

If you look back on energy of any agency you will find the sun is the source for all energy. Hence let us cite that as the first example. The solar energy in the form of solar heat is widely used in various types of solar heaters. Water and wind are among the important natural agencies which are considered as important energy resources. Water can be stored at high altitudes in the form of dams and its potential energy can be converted into kinetic energy by flowing the water through pen stocks. The turbines coupled to electrical generators are fitted below the pen stocks to convert the kinetic energy to electrical energy.

Almost the same principle is used in wind mills which uses the wind forces to generate electrical power. The energy resource of earth are items like coal, petroleum oils and other mineral products. These products have high calorific values and release high thermal energy which in turn is transformed for useful purpose.

## Energy Solutions

In the context of this article, energy solutions mean that energy equations arise due to conservation of energy. We will explain such energy solutions with examples.

### Solved Examples

Question 1:
An object of 5 kg is placed at an height of 10 meters. Suppose the object is freely dropped, what is the velocity of the object when it hits the ground?

Solution:

First let us calculate the potential energy P of the object when it was at a height of 10 meter.
It is calculated as,
P = 5 $\times$ 9.8 $\times$ 10 = 490kgm/s2
Let ‘v’ meter per second be the velocity of the object when it hits the ground. The kinetic energy K acquired by the object at this point is given by
K = $\frac{1}{2}$(5)(v2) kgm/s2

When the object hits the ground, the entire potential energy has become 0 because the height has become 0. But as per conservation of energy this must be equal to the kinetic energy acquired. Therefore, E = P and hence,
$\frac{1}{2}$(5)(v2) kgm/s2 = 490kgm/s2

From the above equation ‘v’ can be solved as 14. That is, the object hits the ground with a velocity of 14 meters per second.

Question 2:
100 kg of water is heated on a 3 kw electric heater for 1 hour. If the initial temperature of the water was 20°C, what would be its final temperature?

Solution:

First let us calculate the electrical energy E consumed by the heater. It is given by,
E = 3kw $\times$ 1hr = 3 kwh
= $\frac{3}{2.78\times10^{-7}}$ joules
= $\frac{3}{2.78}$ $\times$107$\times$ 2.39 $\times$ 10-4 kilo calories
= 2580 kilo calories

The thermal energy H acquired in kilo calories by the water is given by,
H = M $\times$ s $\times$ T,
where 'M' is mass, 's' is the specific heat, which is 1 in this case and 'T' is the temperature rise in oC.
= 100$\times$1$\times$ T = 100T kilo calories.

As per conservation of energy, H = E and therefore,
100T = 2580, which gives the temperature rise as 25.8°C
Therefore the final temperature of water would be (20 + 25.8) °C = 48.8 °C

 More topics in Energy Conservation of Energy Types of Energy States of Matter
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