WORK
 |
| Work,Energy,Power |
Work is said to be
done,if a force acting on a body is able to actually move it through some
distance in the direction of the force is called work.Work is equal to Force
multiplied by Distance.
Work =Force ✕ Distance,
i.e., W= F.S
Its SI unit is a joule
(J).
POSITIVE WORK DONE (EXAMPLES)
When body falls freely
under gravitational pull.
When a horse pulls a
cart on a level road.
NEGATIVE WORK DONE (EXAMPLES)
When a body is made to
slide over a rough surface.When a positive charge is moved towards another
positive charge.
ZERO WORK DONE (EXAMPLES)
When a coolie travels on
a platform with a load on his head.
When a body is moved
along a circular path with the help of a string.When a person does not move
from his position but he may be holding any amount of heavy load.
ENERGY
The energy of an object
is its capacity for doing work.It is a scalar quantity and its unit is joule
(J).
Energy can exist in
different forms such as mechanical energy,heat energy,sound energy,light energy
etc.
Mechanical energy is of
two types i.e., kinetic energy and potential energy.
KINETIC ENERGY
The energy possessed by
a body by virtue of its motion is called its kinetic energy.
A body of mass m and
moving with velocity v has
kinetic energy =1/2
mv2 = P2/2m
When momentum is doubled
kinetic energy becomes four times.
EXAMPLES
Kinetic energy of air is
used to run wind mills.
Kinetic energy of
running water is used to run the water mills.
A bullet fired from a
gun can pierce a target due to its kinetic energy.
POTENTIAL ENERGY
It is the energy
possessed by a body by virtue of its position.
Suppose a body is raised
to a height h above the surface of the earth,then potential energy of body = mgh
EXAMPLES
The potential energy of
the wound spring of a clock is used to drive the hands of the clock.
Due to potential energy
of the stretched bow,the arrow goes forward with a large velocity on releasing
the bow.
The potential energy of
water in dams is used to run turbines in order to produce electric energy using
the generators.
PRINCIPLE OF CONSERVATION OF ENERGY
Energy can neither be
created nor destroyed but can only be transformed from one form to another.
The total amount of
energy in the universe remains constant.
The body falls its
potential energy decreases but, at the same time kinetic energy increases by an
equal amount.
TRANSFORMATION OF ENERGY
In a heat engine heat
energy changes into mechanical energy.In the Sun, mass changes into radiant
energy.
In an electrical
heater,the electric energy is converted into heat energy.
In an electric bulb,the
electric energy is converted into light energy.In burning coal,oil etc, the
chemical energy changes to heat energy.
When we rub our hands,
heat is generated.Here mechanical energy of muscles is converted into heat
energy.
In an electromagnet, the
electric energy is converted into magnetic energy.
MASS-ENERGY EQUIVALENCE
In 1905,Einstein proved
the relation between mass and energy.
E = mc2,
where c is the velocity of light.
E = mc2, leads
to verification of the two laws-law of conservation of mass and law of
conservation of energy.
POWER
The time rate of doing
work is called power.
If W is work done in
time t then power P, is P = W/t
Power is a scalar
quantity with SI unit Watt or Joule/s.
1 watt hour = 3600 joule
1 kilowatt hour = 3.6 ✕ 106 J
1 HP = 746 watt
1 comments:
Click here for commentsGood job it's a very clear explanation
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