4. 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.
5. 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 .
6. • 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.
7. 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.
8. • 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.
9. 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.
10. • 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
12. What is ENERGY?
• The ability of a body to do
work.
• Energy is useful to mankind.
13. Chemical Sound
Electrical
Mechanical Magnetic
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14. Chemical energy is the energy
stored in the bonds of atoms and
molecules. This a form of
potential energy until the bonds
are broken. Fossil fuels and
biomass store chemical energy.
Products that contain chemical
energy include: TNT, baking soda,
and a match. Biomass, petroleum,
natural gas, propane and coal are
examples of stored chemical
energy.
Forms of
Energy
15. Electrical energy is the
movement of electrons.
Lightning and static
electricity are examples of
electrical energy that occur
naturally. Science hasn't
found a way to use natural
forms of electrical energy,
like lightning. Instead, we
use different energy sources
to create electrical energy by
using generators and
turbines.
Forms of
Energy
16. Nuclear energy is the
energy stored in the nucleus
of an atom. Nuclear energy
is unusual in that it can give
off energy in the form of
light or heat. Submarines,
power plants, and smoke
detectors all use nuclear
energy. Nuclear power
plants use uranium, a
radioactive element, to
create electricity.
Forms of
Energy
17. Sound energy is the
movement of molecules in the
air that produces vibrations.
Alarms, music, speech,
ultrasound medical
equipment all use sound
energy. VCR tapes change
sound energy into electrical
energy. The electrical energy
records the sound using
magnetic tape. Speakers read
the magnetic tape and change
it back into sound.
Forms of
Energy
18. Mechanical energy is the
movement of machine parts.
Mechanical energy is also the
total amount of kinetic and
potential energy in a system.
Wind-up toys, mechanical
machines are examples of
mechanical energy. Wind
power uses mechanical energy
to help create electricity.
Potential energy + Kinetic energy =
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19. Magnetic energy is the
attraction of objects made of
iron. Medical equipment,
compass, refrigerator
magnets are all examples of
magnetic energy. Any type of
energy source that uses a
generator in the process to
make electricity uses
magnetic energy.
Forms of
Energy
20. • 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
earth's gravitational field. The potential energy
of an object in this case is given by the relation:
• PE = mgh
22. Work is the transfer of energy through motion. In
order for work to take place, a force must be exerted
through a distance. The amount of work done
depends on two things: the amount of force exerted
and the distance over which the force is applied.
There are two factors to keep in mind when
deciding when work is being done: something has to
move and the motion must be in the direction of the
applied force. Work can be calculated by using the
following formula: Work=force x distance
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23. Work is done on the
books when they are
being lifted, but no
work is done on
them when they are
being held or
carried horizontally.
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24. • 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 .
25. Product of the applied force and the
displacement of an object in the
direction of the applied force
W=F.s
W = work done
F = force
s = displacement in the direction of the
force
26. 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
27. • 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
28. Relationship of work and
energy
When we lift an object (this book, for example) from one
level to another (say,
from the floor to a shelf on the wall), we expend our
energy – by doing work – to increase
the energy stored in the object. (This energy can be
converted back into work, for example,
if we let the book fall back to the floor.) In this
transformation, the chemical energy stored
in our muscles is converted to work, or more precisely to
mechanical energy, and work is
converted into the potential energy stored in the object
(while it sits on the shelf).
29. 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.
30. Difference between Work and
Energy
Work Energy
Work is the transferring of an Energy is all defined as the ability to
energy’s amount via a force push or pull by exertion in a certain
through a distance via the direction path or distance.
of the force.
A block displaced along a table by Examples of energy are nuclear
force (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 or
W=F.d P.E=mgh
