# Lesson Notes By Weeks and Term - Junior Secondary School 2

WORK, ENERGY AND POWER

TERM: 2nd TERM

SUBJECT: BASIC SCIENCE

CLASS:  JSS 2

REFRENCE

• Precious seed BASIC SCIENCE FOR JUNIOR SECONDARY SCHOOLS BOOK 2

WEEK ONE                                                                                       DATE:………………..

TOPIC: WORK, ENERGY AND POWER

Work

Work results when a force acts upon an object to cause a displacement (or a motion) or, in some instances, to hinder a motion. Three variables are of importance in this definition - force, displacement, and the extent to which the force causes or hinders the displacement. Each of these three variables find their way into the equation for work.

That equation is:

Work = Force × Displacement

W = F × d

Since the standard metric unit of force is the Newton and the standard metric unit of displacement is

the meter, then the standard metric unit of work is a Newton•meter, defined as a Joule and abbreviated with a J.

Evaluation

1. What is work?
2. What is the standard unit of work?

Energy

Energy is defined as the amount of work a physical system is capable of performing. Energy, can neither be created nor consumed or destroyed.

Energy, however may be converted or transferred to different forms: The kinetic energy of moving air molecules may be converted to rotational energy by the rotor of a wind turbine, which in turn may be converted to electrical energy by the wind turbine generator. With each conversion of energy, part of the energy from the source is converted into heat energy. We mean that part of the energy from the source cannot be used directly in the next link of the energy conversion system, because it is converted into heat. E.g. rotors, gearboxes or generators are never 100 per cent efficient, because of heat losses due to friction in the bearings, or friction between air molecules.

Note: Energy is measured in Joules (J)

EVALUATION

1. What do you understand by the word energy?
2. What is the unit of energy?

Power

Electrical power is usually measured in watt (W), kilowatt (kW), megawatt (MW), etc. Power is energy transfer per unit of time.

Power may be measured at any point in time, whereas energy has to be measured during a certain period, e.g. a second, an hour, or a year. If a wind turbine has a rated power or nameplate power of 1000 kW, that tells you that the wind turbine will produce 1000 kilowatt hours (kWh) of energy per hour of operation, when running at its maximum performance (i.e. at high winds above, say, 15 metres per second (m/s)).

The power of automobile engines are often rated in horsepower (HP) rather than kilowatt (kW). The word "horsepower" may give you an intuitive idea that power defines how much "muscle" a generator or motor has, whereas energy tells you how much "work" a generator or motor performs during a certain period of time.

Concepts of work, energy and power

Virtually every day we see people carry out various task such as pulling or pushing objects towards a distance. It is observed that force is applied when carrying out the aforementioned activities .It is also pertinent to note that many activities which involve human fatigue do not necessarily, imply that mechanical work is done.  For instance, if a man carries a heavy load  on his head or his hands , no work is being done if the load is kept stationary.

Evaluation:

1. Define the following terms: A.Work B. EnergyC. power
2. What is the unit of energy?

FORMS OF ENERGY

Gravitational energy - Stored energy in raised objects e.g. Sky divers

Chemical energy -   Stored energy in fuel, foods and batteries e.g. Organic food

Sound energy -    Energy released by vibrating objects e.g. Guitar

Electrical energy -  Energy in moving or static electric charges e.g. Lightning

Elastic potential –Stored energy in stretched or squashed objects. E.g. Catapult

Nuclear energy -   Stored in the nuclei of atoms. e.g. Nuclear fuel assembly

Light energy -  Also called radiant energy. i.e energy from the sun. e.g. Sunlight

Kinetic  energy -   that  energy exhibited by a moving body or object. e.g. A bullet cutting a playing card. The energy in moving objects. Also called movement energy.

Potential energy -  is the energy exhibited by a body or object due to its position..

Mechanical  energy -  The sum of (usually macroscopic) kinetic and potential energies

Mechanical wave energy -  a form of mechanical energy propagated by a material's oscillations

Chemical  energy -  that contained in molecules.

Electric energy -   that from electric fields

Magnetic energy -  that from magnetic fields. E.g. Energy in magnets and electromagnets

Nuclear energy -  is the energy released by that of binding nucleons to form the atomic nucleus

Ionization energy - energy involved in binding an electron to its atom or molecule

Elastic energy - that of deformation of a material (or its container) exhibiting a restorative force

Gravitational energy -   that from gravitational fields

Heat energy -  an amount of thermal energy being transferred (in a given process) in the direction of decreasing temperature. E.g. burning match. Also called thermal energy

Mechanical work energy -  an amount of energy being transferred in a given process due to displacement in the direction of an applied force.

Precious seed BASIC SCIENCE FOR JUNIOR SECONDARY SCHOOLS BOOK 2 PAGE 115-119

EVALUATION

1. State the law of conservation of energy.
2. List five forms of energy

GENERAL EVALUATION

1. Define the following terms : A. Work B. Energy  C. power
2. State the law of conservation of energy.
3. List five forms of energy.
4. What do you understand by the word energy?
1.  What is the unit of energy?

WEEKEND ASSIGNMENT

1. The mainspring to all life activities is the A. energy B. power C. work D. force
2. ---------- is the amount of work a physical system is capable of performing. A. Energy B. Work C. Power D. Force
3.  --------- is the sum of (usually macroscopic) kinetic and potential energies
1. Mechanical B. Mechanical Wave C. Mechanical Advantage d. Potential
1. --------- results when a force acts upon an object to cause a displacement (or a motion) or, in some instances, to hinder a motion. A. Work B. Power C. Energy
1. Potential
1. The law of conservation of energy is also known as ---- A. First law of thermodynamic B.  Law of mass action C.  Pythagoras theorem D. None

THEORY

1. 1. Define the following terms: A. work B. energy C. power
2. List five forms of energy and explain.