TERM: 2nd TERM
SUBJECT: BASIC SCIENCE
CLASS: JSS 2
WEEK ONE DATE:………………..
TOPIC: WORK, ENERGY AND POWER
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.
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)
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.
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
© Lesson Notes All Rights Reserved 2023