Energy Energy is an indirectly observed quantity that is often understood as the ability of a physical system to do work on other physical systems. Energy came from the Greek word “energeia” meaning “activity or operation.” It was used in one of Aristotle’s works in as early as the 4th century BC.
Work• In physics, mechanical work is a scalar quantity that can be described as the product of a force and the distance through which it acts in the direction of the force. The term work was first coined in 1826 by the French mathematician Gaspard-Gustave Coriolis .
• If a constant force of magnitude F acts on a point that moves a distance d in the direction of the force, then the work W done by this force is calculated as W=F.d W= work done F= force d= displacement in the direction of the force• For example, if a force of 10 newton (F = 10 N) acts along point that travels 2 meters (d = 2 m), then it does the work W = (10 N)(2 m) = 20 N m = 20 J.
Basic concept• Energy is the ability to do work. However, to understand energy we must understand what scientists mean by “work.” It might seem that it is work to try to solve a problem or to stand at attention for 15 minutes. But that is not “work” to a scientist. In science, work is motion against resistance. Lifting a box against the pull of gravity is work, as is driving a nail into a board against the friction of the wood or winding a clock against the resistance of the spring.
• In doing this work (or any other kind), energy is used up. Both work and energy are measured according to the distance an object is moved and the force that must be overcome to keep the object moving. Suppose a pound of iron is lifted 1 foot. Then 1 foot-pound of work has been performed and 1 foot-pound of energy has been used up.• We need energy to do any kind of work. If someone says that he does not have the energy required to do the job, he is merely reiterating this work energy relationship. Energy is like currency in hand which you use for shopping. Greater the energy you have, more is the amount of work you can perform.
Summary• Energy is the ability to produce or create work. Work, on the other hand, is the ability to provide force and a change in distance to an object.• There are many types of energy such as solar energy, etc., but there is only one type of work.• Energy was coined since 4 BC while work was only used in 1826.• Both work and energy are scalar units.
• Both work and energy are measured in joules.• Work is transfer of energy• Work is done on an object when you transfer energy to that object• The change in the kinetic energy of an object is the net work done on it• The rate of doing work is same as that of consuming energy
What is ENERGY?• The ability of a body to do work.• Energy is useful to mankind.
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Chemical energy is the energystored in the bonds of atoms andmolecules. This a form ofpotential energy until the bondsare broken. Fossil fuels andbiomass store chemical energy.Products that contain chemicalenergy include: TNT, baking soda,and a match. Biomass, petroleum,natural gas, propane and coal areexamples of stored chemicalenergy. Forms of Energy
Electrical energy is themovement of electrons.Lightning and staticelectricity are examples ofelectrical energy that occurnaturally. Science hasntfound a way to use naturalforms of electrical energy,like lightning. Instead, weuse different energy sourcesto create electrical energy byusing generators andturbines. Forms of Energy
Nuclear energy is theenergy stored in the nucleusof an atom. Nuclear energyis unusual in that it can giveoff energy in the form oflight or heat. Submarines,power plants, and smokedetectors all use nuclearenergy. Nuclear powerplants use uranium, aradioactive element, tocreate electricity. Forms of Energy
Sound energy is themovement of molecules in theair that produces vibrations.Alarms, music, speech,ultrasound medicalequipment all use soundenergy. VCR tapes changesound energy into electricalenergy. The electrical energyrecords the sound usingmagnetic tape. Speakers readthe magnetic tape and changeit back into sound. Forms of Energy
Mechanical energy is themovement of machine parts.Mechanical energy is also thetotal amount of kinetic andpotential energy in a system.Wind-up toys, mechanicalmachines are examples ofmechanical energy. Windpower uses mechanical energyto help create electricity.Potential energy + Kinetic energy = Next
Magnetic energy is theattraction of objects made ofiron. Medical equipment,compass, refrigeratormagnets are all examples ofmagnetic energy. Any type ofenergy source that uses agenerator in the process tomake electricity usesmagnetic energy. Forms of Energy
• Kinetic Energy: Everything you see moving about has kinetic energy. The kinetic energy of an object in this case is given by the relation: • KE = (1/2)mv2• Potential energy : Potential energy exists whenever an object which has mass has a position within a force field. The most everyday example of this is the position of objects in the earths gravitational field. The potential energy of an object in this case is given by the relation: • PE = mgh
Work is the transfer of energy through motion. Inorder for work to take place, a force must be exertedthrough a distance. The amount of work donedepends on two things: the amount of force exertedand the distance over which the force is applied.There are two factors to keep in mind whendeciding when work is being done: something has tomove and the motion must be in the direction of theapplied force. Work can be calculated by using thefollowing formula: Work=force x distance Main Menu Next
Work is done on thebooks when they arebeing lifted, but nowork is done onthem when they arebeing held orcarried horizontally. Main Menu
• Work is done… …by a force when the object it acts on moves NO work is done by pushing against a stationary wall. • Work IS done throwing a ball because the ball MOVES while being pushed during the throw .
Product of the applied force and the displacement of an object in the direction of the applied force W=F.sW = work doneF = forces = displacement in the direction of the force
Examples• If a box is pushed with a force of 40 N and is moves steadily through a distance of 3 m in the direction of the force, calculate the work done.Solution: F= 40 N s =3m Work done, W = Fs = 40N x 3m =120J
• A woman pulls a suitcase with a force of 25 N at an angle of 60o with the horizontal. What is the work done by the woman if the suitcase moves a distance of 8 m along the floor.• Solution: F = 25 N s=8m 0 60o W = 25 cos 60 x 8 = 100 J
Relationship of work and energyWhen we lift an object (this book, for example) from onelevel to another (say,from the floor to a shelf on the wall), we expend ourenergy – by doing work – to increasethe energy stored in the object. (This energy can beconverted back into work, for example,if we let the book fall back to the floor.) In thistransformation, the chemical energy storedin our muscles is converted to work, or more precisely tomechanical energy, and work isconverted into the potential energy stored in the object(while it sits on the shelf).
Direction of Force• When a force and the distance through which it acts are parallel, the work done is equal to the product of F and d• If the forces are NOT parallel, work done is equal to the product of d and the projection of F in the direction of d.
Difference between Work and Energy Work EnergyWork is the transferring of an Energy is all defined as the ability toenergy’s amount via a force push or pull by exertion in a certainthrough a distance via the direction path or distance.of the force.A block displaced along a table by Examples of energy are nuclearforce (F) and distance (D) energy, solar energy, electrical energy, and a lot more.It is mathematically given as It is either given as K.E= 1/2mv² orW=F.d P.E=mgh