# Energy: Applications and Uses - Module 3 (Physics and Technology)

Updated on January 13, 2020
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## objectives

1)Define energy and give its S.l unit.

2) List forms of energy.

3) Give the advantages of solar energy.

4) Distinguish between renewable and non — renewable energy sources and give examples.

5) State the law of conservation of energy.

6) Define conduction, convection, and radiation as processes of heat transfer.

7) Distinguish between hard and soft magnetic materials.

8) Define force and state the type of forces that oppose the relative motion.

9) Define speed and state its S.l unit.

## Meaning of Energy

Children need the energy to walk to school, run around, climb a tree and play football. They obtain this energy from the food they eat. Radios, televisions, and computers need the energy to function. This energy may' be obtained from electricity. Cars, airplanes and moto cycles need the energy to operate. This energy is obtained from fuels. In anything that we do and in everything happening around us, energy is involved. Energy is, therefore, the ability to get things done or to get things going. This means that work is done each time energy is used. A person who has a lot of energy is also capable of doing a lot of work. Energy is therefore defined as the ability to do work.

## Classes of energy

Basically, energy can be classified into two general types: kinetic

energy and potential-energy.

## Kinetic energy

The word kinetic comes from the Greek word “Kinetos” which means moving. Kinetic energy is the energy an object has because it is moving. This energy can be released by stopping the object. A running car has kinetic energy because it is moving. If the car hits an obstacle and stops moving, the kinetic energy will be released and as such, cause some damage to the obstacle. A larger bus moving at a higher speed will cause more harm to the obstacle if it had hit the same obstacle. This is because the bus had more kinetic energy due to its larger mass and speed. That is, the kinetic energy of a moving object depends on its mass and speed.

## Potential energy

It is the energy stored in an object because of its position or shape.

Potential energy exists in two forms.

a) Gravitational potential energy: It is the energy stored in an object raised above the earth’s surface. Potential energy increases when the object is raised to a higher level. The energy is released as the object forms.

b) ELASTIC potential energy: When an object is stretched or the relative positions of its particles are changed here, the shape of object changes. The energy used to change the shape of the object in them stored in the object as elastic potential energy.

## Forms of energy

The major forms of energy are as follows:

## a) Mechanical energy

It is the sum of an object’s kinetic energy and potential energy. That is the sum of the energy due to motion and the energy due to the position of an object.

## b) Heat energy

Heat is a form of energy that is associated with the motion of atoms molecules of a body. It is the energy of hotness. When the atoms of the object move faster, the object’s thermal energy increases and it becomes warm. Heat energy usually flows from one body to another because of temperat difference. It flows from a hotter body to a cooler body.

## c) Electrical Energy

This is the energy that is due to the motion of charges in conductors. That is, the motion of electrons and/or ions produces current electricity which is the source of electrical energy.

## d) Light energy

It is the energy that enables us to see. It is detected with the eye. It is impossible to store light energy because it radiates away or turns to heat.

## e) Sound energy

It is the energy produced by a vibrating object. A drum being played, an e that is ringing, a loudspeaker that is playing all produce sound energy by vibrating.

## d) Chemical energy

It is the energy stored in the chemical bonds of compounds. Chemical energy is stored in fuels such as the food we eat, petrol, gas, wood etc. It is released in a chemical reaction such as burning.

## f) Nuclear energy

This is energy stored in the nucleus of an atom. It is released at nuclear power station during a nuclear reaction or when an atomic bomb explodes.

## g) Solar energy

This is energy from the sun.

## Sources of energy

An energy source is the starting point (i.e origin) of energy. Or it is simple where energy comes from. Energy sources include;

The Sun

Almost all the energy used on earth comes directly or indirectly from the sun. In fact about 99 % of the world’s energy can be traced back to the sun. Plants use solar energy in the process of photosynthesis to manufacture their food. Animals get their food from the plants. When the remains of these animals are buried and compressed for millions of years, the fuels that we use for our daily activities (coal, oil, petrol, gas) are formed. Hence, foods and fuels store energy from the sun. Energy from the sun is used for food , preservation, drying of grains etc.

## Renewable and non - renewable energy source

A renewable energy source is replenished naturally. It is also referred to as an infinite or a regenerative or an inexhaustible, Other source examples of renewable energy in clude: Water, wind, geothermal and biomass.

On the other hand, we have non - renewable energy sources. These are those that are limited. Once used, they cannot be replenished. This means that they can be completely used up one day. They are also referred to as finite or non - regenerative or exhaustible energy sources. Examples are; wood, fossil fuels (petrol, gas, coal)

## Some non - renewable energy source

1) Wood

This is a very essential energy source especially when it is dry, mostly in the developing countries like those found in Africa. Dry wood is used for, cooking, drying of crops (cash crops like cocoa) and others. Wet wood is mainly used for the production of coal which is used by blacksmiths and other* business persons along the road and at business centers. This is found most towns today

2) Fossil (coal, oil and gas)

Fossil is any fuel formed from the remains of ancient plants and animal life. It is formed in this manner: microscopic plants and animal collect in layers of mud forming organic rich ooze. This organic rich layer is underlain and overlain with settled rock. Heat and pressure “cook” the ooze, causing oil to form. Geological forces cause the rock layers to bend. The oil is forced out, migrates into porous rocks ad it trapped.

## Frictional force

If a car is rolling on a flat street, it will keep on rolling if no force is acting on it. That is, it will keep moving with constant velocity. But on the contrary, the car will keep slowing down until it eventually stops. This steady change in the velocity of the car suggests that a force is acting on it. This force which acts in a direction opposite to the direction of the car’s motion is called friction. Friction is the force between two bodies in contact that opposes the motion of either body. It is because of friction that a constant force must be applied to a car on a flat road just to keep it moving. The forces acting on the car must be unbalanced since the net force has to cause the car to attain a certain velocity from rest. Thus, the force pushing the car forward (the force from the engine) must be greater than the force of friction opposing the car’s motion.

## Air Resistance

Frictional force between the tires of a car and the road enable the car to move. However, another drag force called air resistance opposes the car’s motion. Air resistance is a force that is caused by the interaction between the surface of a moving body and the air molecules.

The amount of air resistance on a body depends on;

- The object size

- The object shape and

- The speed with which the object is moving.

Objects with large surfaces experience large air resistance and air resistance also increases with increase in the speed with which the body is moving. Car design has changed significantly over the years. With the need for better fuel efficiency and increased speed, car designs have been changed to reduce air resistance on them.

To make cars, trains and planes move faster without using more fuel, designers have changed the shapes of these vehicles to reduce the air resistance between the vehicles and the surrounding air.

## Gravity

This is the attraction between two particles of matter due to their mass. Gravity explains why an apple falls from a tree. Every object exerts a gravitational force on another. When an apple cuts from its stem, the apple falls down because the gravitational force between the earth and the apple is much greater than the gravitational force between the apple and the tree. The force of gravity is different from air and frictional force between it acts even when the objects are not touching. Secondly, air resistance and frictional forces exist only when objects are in relative motion but gravity exists even when objects are not moving. Gravitational force decreases rapidly with increase in distance between the two bodies.

## Effects of Forces on their Target

1) A force can reduce or increase the velocity of an object or stop it from moving.

2) A force can change the shape or volume (or both) of an object. This effect is slight for hard objects but very noticeable with flexible ones.

3) A force can cause an object at rest to start moving.

4) A force can change the direction of motion of an object.

5) A force can cause an object to break.

## Magnetism

Magnetism refers to physical phenomena arising from the force between magnets, objects that produce fields that attract or repel other. All materials experience magnetism, some more strongly than others. Permanent magnets made from materials such as iron, experience the strongest effects, known as ferromagnetism. This is the only form of magnetism that is strong enough to be felt by people. Some materials are called non - magnetic, because their magnetic effects are so small. Magnetism can also vary depending on temperature and other factors.

## Magnetic Force

Magnetic fields exert a force on particles in the field. The motion of electrically charged particles gives rise to magnetism. The magnetic force acting on a single electric charge depends on the size of the charge, its speed, and the strengths of the electric and magnetic fields. A magnet is a substance that has the ability to attract some substances placed near to it. This property is called magnetism. Materials which are attracted or affected by magnets are called magnetic materials. They include; iron, nickel, cobalt and a number of alloys (alloys a^e mixtures of these metals that have been melted together) and recently developed groups of materials called ferrites. These groups are called Ferro magnetic or ferromagnetism.

## Properties of magnets

a) If a small bar magnet is dipped into iron filings, the filings will be attracted to its ends most. This means that a magnet has a force that it uses to attract magnetic materials. This force is strongest at the ends. This ends where the magnetic force seems to originate or is strongest are called the poles of the magnet.

b) Suspended magnet

The earth behaves like a giant magnet. The earth then exerts a force on the poles of a magnet. If a bar magnet is suspended as shown, it will swing round or oscillate until it will come to rest lying in the north south direction. This behavior is used to name the two poles of a magnet. The end of a magnet which points roughly northwards is called the north seeking pole or simply North Pole, while the other end is the south seeking pole or South Pole.

## Types of Magnets

Magnets aie of two main types namely; permanent and temporal

magnets. There are different types of permanent magnets namely bar magnet, which is either a rectangular bar or a cylindrical rod. There are two types of horseshoe magnet, the loudspeaker magnet that has a central N -pole surrounded by a S - pole and produces a radial field. At the other end, there is a S-pole surrounded by a N-pole. The last type is the moving coil meter magnet. It has a curved N-pole and S-pole with a soft iron cylinder between them. This also produces an approximately radial field. The earth is a giant magnet.

## Magnetic and Non - Magnetic Material

Magnetic material: This is a material that can be attracted by a magnet and it can be converted to a magnet. That is, can be magnetized. Examples of magnetic materials include; iron, nickel and cobalt. They can be used to produce hard and soft magnetic materials. Hard magnetic materials such as steel (an alloy of iron) can be used to produce a hard magnet. Hard magnets are permanent magnets. The)' can keep their magnetism for long. Soft magnetic materials like iron can only be used to make temporal magnets. Temporal magnets do not keep their magnetism for long.

## Non - Magnetic Materials

These are materials that cannot be converted into magnets or cannot be magnetized. Examples include metals such as; brass, copper, zinc, tin, aluminum as well as non - metals.

## Work

Energy is that which enables work to be done. Work is the energy transferred by a force when it moves. Energy is sometimes called work. Work is moved energy. Work is said to be done when a force applied on an object causes it to move in specific destination.

## Motion

Motion is the change in position of an object with time. Motion is common in everyday life. For example we are surrounded by moving things; from vehicle moving in straight line to a satellite moving in a circle around the earth.

## Speed

Speed tells us how fast or slow a body is moving. Speed is defined as the rate of change of distance with respect to time. The speed of a body.

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