3. 3
Forms of Energy
Energy exists in many different forms. We cannot “see” energy, but we can see its effect.
4. 4
What is Energy?
The car is powered by petrol, a form of stored energy. The energy from the sun
makes plant grow.
Light bulbs glow because of electrical energy. Food gives us energy to live, grow,
move and work. We burn food we eat to get energy.
Energy is the ability to do work. Work means lifting or moving
something, warming or lighting something. Energy causes things
to happen around us.
5. ENERGY
We have natural energy
sources such as the sun,
wind, water at a height,
tides, etc.
We also have other
energy sources such as
petroleum, natural gas,
etc.
6. Units Of Energy
Joule is a very small unit of energy.
Commercial unit of energy is kilowatt-hour(kWh).
One calorie = 4.2 joule
489 x 4.2 = 2053.8 J
1 kcal = 1000 calorie
One kilowatt-hour is defined as the amount of
energy consumed when an electrical appliance of
1000 watt power rating is used for 1 hour.
The relation between joule and kilowatt-hour is
given by :-
1kWh = 3600000 Ws = 3.6 x 106
J
7. 7
Forms of Energy
Potential Kinetic
Mechanical energy is divided into two main types:
•Energy that is stored or
contained within a substance
•It is the energy available to
make a change happen
•Potential energy exists
because of the object’s
position or because of the
chemical arrangement of its
parts.
•Energy of motion
•It is the energy
present in an object
in motion
Stored chemical energy in a battery Kicked football Waterfall
9. POTENTIAL ENERGY
Elastic potential energy
• Potential energy possessed
by a body by virtue of its
configuration is known as
elastic potential energy
• E.g. the stretched string of a
bow
Gravitational potential energy
• Potential energy possessed
by a body by virtue of its
position with respect to the
ground is known as
gravitational potential
energy
• E.g. a ball at a height
18. Law Of Conservation Of Energy
Energy can neither be created nor
destroyed. It can only be transformed
from one form to another.
For example, the chemical energy of
food we eat gets converted into
muscular energy that can be used to
do work such as cycling, walking, lifting
a load, etc.
During cycling, the muscular energy of
the cyclist is converted into the kinetic
energy of the bicycle that helps him
move forward.
The total energy of the system (cyclist
+ bicycle) remains unchanged i.e.,
muscular energy + kinetic energy
remains unchanged during cycling.
19. STATE THE LAW OF CONSERVATION OF ENERGY.
GIVE AN EXAMPLE FOR CONSERVATION OF
ENERGY.
