class 9
physics
chapter 4
Work and Energy
Work
Work is
done when a force produces motion.
The work done by a force on a depends on two
factors.
1.
Magnitude of the
force
2.
Distance through
which the body moves
Work
done in moving body is equal to the product of force exerted on the body and the distance moved by the body in the
the direction of a force.
Work = Force *
Distance
|
W= F*s
·
The SI Unit of
Work is J.
·
Work is a scalar quantity
·
The conditions for a force to do the work is that it should
produce motion in an objects.
Work was done against Gravity
Whenever work is done
against gravity, the amount of work done is equal to the product of the weight of the body and the
vertical distance through which the body is lifted.
Work was done in lifting a body = Weight of body *
Vertical Distance
W= m*g*h
|
Work done by a Force Acting Obliquely
In many cases, the movement of the body is
at an angle to the direction of the force applied.
W = force* cos theta * distance
Positive, negative, and zero
1. Work done
in positive when a force act in the direction of motion of the body.
2. ➧
Work done is negative when a force act opposite to the direction of
the motion of the body.
3. Work done
is zero when a force act at right angles to the direction of the motion of the
body.
Energy
Energy is the ability to do work.
· Energy is a scalar quantity.
· The SI unit of energy is jule.
A different form of Energy
. ⧫ Kinetic
energy
2. ⧫ Potential
energy
3. ⧫ Chemical
energy
4. ⧫ Heat energy
5. ⧫ Light energy
6. ⧫ Sound
energy
7. ⧫ Electrical
energy
8. ⧫ Nuclear
energy
Kinetic energy
The energy of the
body due to its motion is called kinetic energy.
The formula of kinetic energy
The kinetic
energy of a moving body is measured by
the amount of work it can do before coming to rest.
Kinetic energy = 1/2m
v2
Potential energy
The energy of a body
due to its position or change in shape is knows as potential energy
The gravitational potential energy as well as elastic energy
are commonly known as just potential energy.
Formulas of potential energy
Potential energy = m*g*h
{ m= Mass of the object , g = Gravity
h = Height of the body above a reference point, say the surface of the earth}
Power
➧Power is defined as the rate of doing work.
Power = Work done / time taken
OR P
= W/t
Power = energy
consumed / time taken
OR
P= E/t
· ➧ Power is
the rate at which work is done energy is consumed.
· ➧Power is a
scalar quantity.
· ➧
The SI unit is power is WATT.
1 WATT= 1
JOULE/1SECOND
SO 1 watt = 1 joule per second
· ➧Watt
is the smallest unit of power.
· ➧ 1
kilowatt = 1000Watts
· ➧
1kw = 1000W
· ➧
1mega
watt = 1000,000watts
· ➧
1MW
= 106 W
COMMERCIAL UNIT OF ENERGY
The
commercial unit of energy is kilowatt-hour (KWH).
1KWH= 36,00,000 joules.
TRANSFORMATION OF ENERGY
The change of one form of energy into another form of energy
is knows as the transformation of energy.
ENERGY TRANSFORMATION AT A
HYDROELECTRIC POWERHOUSE
Potential
energy →kinetic energy→ electrical energy.
Energy transformation at a thermal powerhouse.
Chemical energy→ heat energy→ kinetic energy→ electrical
energy.
Using energy converter
Electric iron.
Electrical → heat energy
Radio
Electric energy → kinetic energy→ sound energy.
Steam engine
Heat → kinetic.
Cell
Chemical energy→ electrical.
LAW OF CONSERVATION OF ENERGY
Whenever energy change from one form to another form, the total
amount of energy remain constant.
·
Energy can neither be created nor destroyed.
The swinging simple pendulum is an example of
conservation of energy.
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