Energy 

Energy is the force that makes everything happen in the universe. From the rotation of planets in the Universe to the glow of a light bulb, energy drives our world in so many ways. It is available in many forms, such as the sun's heat and the spark of electricity, and is the key to life, technology, and advancement. The energy stored in food that powers our bodies or the energy produced by wind and solar systems to power our homes, understanding energy is the main component of designing a sustainable and innovative world.

1.0What is Energy? 

Energy is the fundamental concept of science, which is defined as the ability to work to do work or cause change. It is present in various forms and can be transferred or converted from one form to another but can not be created. Energy is not always in a visible form but is always there at work. In simple words, energy is what things happen. Any physical, chemical, or biological process is not possible without energy. 

In the international system of units, the energy unit is joules (J). Other commonly used units of energy are calories or kilowatt-hours (kWh). 

2.0Types of Energy: 

There are different types of energy in the universe, each connected with different sources and physical phenomena. Some common types of energy are:

• Kinetic Energy: KE is the energy of motion. Any moving object, whether it's a car, a flying bird, or even a flowing river, possesses kinetic energy. The kinetic energy an object possesses depends directly on its mass(m) and velocity(v). The kinetic energy can expressed in terms of the following: 

$KE=\frac{1}{2}m{v}^2$

• Potential Energy: Potential energy (PE) is energy that is stored. It relies on the object's position or configuration. The most familiar one is gravitational potential energy, which relies on the height of an object above the ground. The potential energy formula can be expressed as:

$PE=mgh$

The Sum of both potential (PE) and kinetic energy (KE) is known as mechanical energy. 

• Solar Energy: It is a form of energy obtained from the light produced by the sun. Energy is a widely used form of energy due to its easy availability and unlimited source. This energy from the sun is further divided into different types of solar energy, which include: 
• • Solar Thermal Energy: It is used to produce heat for water or air heating and electricity generation.
  • Photovoltaic Energy: Photovoltaic energy directly converts sunlight into electricity with the help of solar cells.
  • Concentrated Solar Power: This is a type of solar energy which utilises mirrors or lenses to concentrate sunlight to produce high-temperature steam for the production of electricity.
• Electrical Energy: Electrical energy is usually produced by the flow of electrons in a conductor. It energises devices from small devices such as smartphones to huge systems such as citywide electrical grids.
• Nuclear Energy: Nuclear energy is contained within the nucleus of atoms. It is released by nuclear reactions like fission (atom splitting) or fusion (atom combining). This energy is utilised in nuclear power plants and the sun.

3.0Energy Density 

Energy density can be defined as the amount of energy that is stored in a unit of volume or weight, the more the energy density, the more the energy is stored in the object. This concept of energy plays an important role in understanding renewable and non-renewable sources of energy. Solar wind and windmills have a lower energy density in comparison to fossil fuels. The formula for energy density can be stated as:

$EnergyDensity=\frac{EnergyStored}{Volumeormass}$

Practically, energy density has applications in various objects, including batteries, fuel, and storage systems, where the space and weight of the object are important. 

4.0Law of Conservation of Energy

The law of conservation of energy is the most famous and important law related to energy, which specifically states that “Energy can neither be created nor be destroyed and can only be converted from one form to another form”. In other words, the total amount of energy in any closed system remains constant over time. This law implies all types of energy irrespective of their source.

To understand this more clearly, imagine a pendulum in which potential energy is transferred to kinetic energy and vice versa. As the pendulum oscillates, the energy goes back and forth between these two forms, but the energy does not change. In real-life situations, some of the energy tends to be lost as heat due to friction, but the overall energy in the system is conserved.

5.0Solved Examples on Energy: 

Problem: A pendulum with a bob of mass 0.5 kg is released from a height of 2 meters above its lowest point. Calculate the speed of the bob when it reaches the lowest point.

Solution: At the maximum height, the potential energy of the pendulum will be maximum, and the kinetic energy will be zero. 

m = 0.5kg (mass of the bob) 

g = 9.8 m/s² (acceleration due to gravity) 

h = 2m 

PE = mgh 

PE = 0.59.82=9.8J

Now, Using the law of conservation of energy: 

PE_initial = PE_final

$9.8J=\frac{1}{2}\times 0.5\times v^2$

$v^2=\frac{19.6}{0.5}=39.2$

$v=\sqrt{39.2}\approx 6.26\text{m/s}$

Problem 2: A ball is dropped from a height of 10 meters. After bouncing, it reaches a height of 6 meters. Assuming energy loss due to air resistance and ground friction, calculate the energy lost in the bounce.

Solution: Before the bounce, 

The Potential energy of the ball at 10 meters = mgh 

PE_Initial = mgh 

${\text{PE}}_{\text{Initial}}=1\times 9.8\times 10=98J$

After the bounce at 6 meters: 

The final potential energy at 6m = mgh 

${\text{PE}}_{\text{Final}}=mgh$

${\text{PE}}_{\text{Final}}=1\times 9.8\times 6=58.8J$

The energy lost during the bounce:

${\text{PE}}_{\text{Initial}}-{\text{PE}}_{\text{Final}}=98-58.8=39.2J$

Problem 3: An electric motor lifts a 10 kg weight to a height of 12 meters in 5 seconds. What is the power required by the motor?

Solution: Given m = 10kg, h = 12m, t = 5seconds

To calculate the power, firstly, we would calculate the work done, which is the same as the energy used, by using the formula: 

PE = mgh 

$\text{PE}=10\times 9.8\times 12$

PE = 1,176 J 

The formula for power $P=\frac{E}{t}$

$P=\frac{1176}{5}=235.2W$