JSS 2: ENERGY

Energy is the ability to do work. It exists in various forms and can be transferred or transformed from one form to another. Energy is essential in every aspect of life and drives all processes in nature and technology.

Types of Energy

1. Mechanical energy

2. Thermal (Heat) energy

3. Chemical energy

4. Electrical energy

5. Nuclear (Atomic) energy

6. Sound energy

7. Light energy

      Mechanical energy

Mechanical energy is the energy that is possessed by an object due to its motion or due to its position.

Types of mechanical energy

The two types of mechanical energy are:

1. Kinetic Energy

Kinetic energy is the energy of a moving object. The S.I. unit of kinetic energy is joules (J)

Formula: K.E. = ½mv²

where: m= mass (kg), v = velocity (m/s).

Example:

(i) What is the Kinetic energy of a 1500 kg car going at a speed of 14 m/s?

Solution:

K.E. = ½mv²

m=1500kg, v=14m/s

K.E=½ x 1500 x 14²

      = 147,000J

(ii) What is the velocity of a 1000 kg car if its kinetic energy is 200 kJ?

Solution:

Kinetic energy= 200KJ=200,000J

m= 1000kg

K.E. = ½mv²

200000 = ½ x 1000 x v²

200000= 500 v²

 V² = 200000/500

V² = 400

V = √400

V= 20m/s

2. Potential Energy

Potential energy is the energy of a body due to its position.

The S.I. unit of potential energy is joules (J)

Formula: P.E. = mgh

where: m = mass (kg),

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

 h = height (m).

Examples:

(i) A mass of 2kg is taken from the ground to the height of 10m. Find the potential energy of the object. (g= 9.8 m/s²)

Solution:

P.E. = mgh

P.E. = 2x 9.8 x 10

P.E. = 196J

(ii) 5 kg weighing cat climbing at the top of the tree has a potential energy of 1000J. Find the height of the tree.(g=10m/s²)

Solution:

P.E. = mgh

1000 = 5 x 10 x h

1000 = 50h

h = 1000/50

h= 20m

2. Thermal Energy

Thermal energy is the energy related to the temperature of an object due to the motion of its particles.

3. Chemical Energy

Chemical energy is the energy stored in chemical bonds, that is released during chemical reactions.

4. Electrical Energy

Electrical energy is the energy associated with the flow of electric charge.

5. Nuclear Energy

Nuclear energy is the energy stored in the nucleus of an atom, that is released during nuclear reactions.

6. Sound Energy

Sound energy is the energy carried by sound waves through a medium.

7. Light Energy

Light energy is the energy carried by electromagnetic waves.

Energy Transformation

Energy can be converted from one form to another. For example:

(a) In a falling object, potential energy transforms into kinetic energy.

(b) In Burning fuel, chemical energy transforms into heat and light energy.

(c) In Power plants, mechanical or chemical energy is transformed into electrical energy.

Sources of Energy

1. Renewable energy sources e.g. Solar, wind, hydroelectric, geothermal, biomass.

2. Non-renewable sources e.g. Fossil fuels (coal, oil, natural gas), nuclear energy.

Laws of Conservation of Energy

(a) Energy cannot be created or destroyed, it can only change from one form to another.

(b) Total energy in a closed system remains constant.

Applications of energy

1. Energy is used in transportation: Cars use chemical energy from fuel.

2. Energy is used in electricity generation: 

3. Energy is used in Industrial processes: Machines use mechanical energy for production.

Assignment

1. Explain the following:

(a) Renewable energy resources

(b) Non-renewable energy resources 

2. Identify three (3) examples of energy transformation in daily life.

3.How fast must a 6.0 kg cat run to have a kinetic energy of 150 J?

4. What is the energy of a baby who weighs 20N sitting in a chair 1.5m high?