1. Work. Energy and
Power
By: Listiya Pawitra
Grade: 11 Science

2. Work
• Work is done when a force move a point at which
it acts in the direction of the force.
• Work done = force x distance moved by force
- When a force moves its point in the direction of
the force, the force works and the work done is
said to be positive.
• Work done is said to be negative, when the work
is done on force, which means that the direction
of the force is opposite to the direction of the
movement.

3. Work done
• Has no direction
• Only has size
• It is a scalar quantity
• Unit measurement is Joule (J)

4. • Initial position Final position of the
foece
Direction of movement of
force
• This diagram shows work si done by force.

5. • Final position Initial position
Direction of force
• This is the diagram of work is done on the
force.

6. Displacement
• It is a vector quantity
• It is another name of distance moves ina
particular direction.
• Work done for displacement x = F cos y x x

7. Work done by an expanding gas
• When gas expands it works breaking down a
concrete building.
• Work done of gas = pressure x change in
volume
• When gas expands work is done by gas
• When gas contracts, work done is done on gas

8. Energy
• The ability to do work is called energy
• Its unit measurement is in Joule ( J )
• There are 2 types of energy:
- Potential Energy
- Kinetic Energy

9. Potential Energy
• Potential energy is the ability of an object to
do work as a result of its position or shape.
• The energy can be called elastic.
• It is a form of energy that is stored in objects
which have had their shape changed
elastically. Ex: a wound up spring, twisted
elastic bands.

10. Electrical Potential energy
• It is the law of charges like charges repel and
attract. This means that repelling an
attracting need work.
• Electrical potential energy increases when 2
positive charges move towards each other and
work is done.

11. Gravitational Potential Energy
• When 2 masses are pulled apart, it causes
work o be done this is gravitational potential
energy.
• If masses move closer together they lose
gravitational potential energy.
Potential energy = mg h

12. Kinetic Energy
• This energy is due to motion.
• When an object moves it gains in kinetic
energy but loses its potential energy.
Kinetic energy = 1/2mv2

13. Energy conversion and conservation
• All the energy changes happening on earth is
governed by the law of conservation of
energy.
• The law states that:
Energy can’t be created or destroyed. It can
only be converted from one from to another.

14. Efficiency
• In energy changes some energy are lost as heat
energy.
• Efficiency gives a measure of how much the total
energy can be used and is not lost.
Efficiency = useful work done / total energy input
It can be given in ratio or percentage.
* Efficiency can never be > than 100% because it
can’t be created.

15. Deformation of Solids
• Deformation occurs when you pull a spring
over its elastic limit.
• Tensile deformation is when there is force that
can stretch it, make it longer, squash it and
make it shorter. The example is a metal
cylinder.

16. Hooke’s Law
• It states that, provided the elastic limit is not
exceeded, the extension of a body is
proportional to the applied force.
• Extension is the increase in length of a spring.
• The load attached to the spring is called the
load.
• Elastic change is when a body or object
returns to its original shape and size when the
load is removed.

17. • Elastic limit is when it is the maximum
elasticity it can reach in order for it to return
to its original size and length.
• Beyond the elastic limit the spring is said to be
plastic.
F=k x
• Unit measurement is Nm-1

18. Strain Energy
• Strained is when an object changed its shape
n=my forces acting on it.
• Strain energy is the energy stored in a body
because of change of shape.
Strain energy W = 1/2k(x)2

19. Young Modulus
• By using the young modulus we can find the
extensions knowing the constant and
dimensions of the object.
• Strain Energy = extension / original length
• The strain produced within an object is
caused by stress.
• Stress = force / area of cross section
• Unit measurement of stress is Nm-2

20. • Young Modulus E = Stress / Strain
• This has no units because it only shows the
ratio.

21. Behaviour of different materials under
tensile stress
X
X is the maximum force
and this is called as
ultimate tensile stress.
Ultimate stress gives a
sign of the maximum
force that the wire can
afford.

22. Graph of brittle materials
Brittle means that it is
delicate and can break
easily.
Brittle materials obeys
the Hooke’s law . There is
very little plastic
deformation that’s why
glass can shatter into
many pieces.

23. Graph of polymeric material showing
hysteresis
Energy dissipated
Elastic hysteresis is when a cord is not
permanently deformed but, when
stretched it just doesn’t return to it’s
original length.
This graph shows that the
strain energy needed to
deform the rubber, area
under the graph is greater
than the work done for
the material to return to
it’s original length.

24. Specific Heat Capacity
• Q = m.c. t
• Q is the energy
• m is the mass ( in kilograms )
• C is the specific heat capacity
t is the change of temperature
• The SI unit of specific heat capacity is J kg-1K-1

25. Thermal heat Capacity
• This is to find the change in heat energy.
• The thermal heat capacity of a body is the
quantity of heat energy needed to increase
the temperature of the whole body by one
degree
• Q=C t
The SI unit of heat capacity is J K-1

26. Specific latent heat
• There are 2 types:
- Specific latent heat of fusion
- Specific latent heat of vaporization

27. Specific latent heat of Fusion
• It is the quantity of heat energy required to
change the mass of solid to liquid without any
change of temperature.
• Q = m . Lf
• Unit measurement is J kg-1

28. Specific latent heat of vaporization
• It is the quantity of heat energy to convert the
mass of liquid to gas with no change in
temperature.
• Q = m.lv
• Unit measurement is J kg-1

29. Power
• Power is the rate of doing work.
• Power = work done / time
• The SI unit of power is watt (W)
• Power is a scalar quantity
• Power = force x speed

30. Kilowatt-hour
• One kilowatt hour is the energy used when
work is done at the rate of 1 kilowatt in 1
hour.
• It is the unit measurement in electricity
meters at home.

31. Moment of a force
• When there is ruler put in horizontal nad
there is a weight attached to it, we can feel a
turning effect on the ruler. This turning effect
is called moment of the force.
• Moment of force depends on the magnitude
and the distance of the forcefrom the pivot

32. • So, the moment of a force is the product of
the force and the perpendicular distance of
the line of action from the pivot.
• Moment of force = F x l.cosx

33. Couples
• Consist of 2 forces
• They have equal magnitude but opposite
direction.
• When you turn a screw driver, It produces a
turning effect. Since there are 2 forces acting
on it, the turning effect is called a torque.

34. The Principle of moments
Hanging a weight on the ruler will
make it the ruler to rotate around
the pivot.
Hanging one weight on one side of
the ruler will make the ruler to
rotate the opposite direction.
Pivot
Hanging 2 weights on both sides of
the ruler will make the ruler to
rotate clockwise or anti clockwise.

35. • Rotational equilibrium is when a body has no
tendency to change its rotation speed.
• The sum of the clockwise moments at any
point must be equal to the sum of
anticlockwise moments at that same point.
• Centre of gravity is a point which the whole
weight of the object looks balance.

36. Equilibrium
• For an object to be at an equilibrium state:
- The total value of the forces in any directions
must be zero.
- The sum of the moments of the forces around
any point must be zero.

37. Thank you
for
Reading!!!!!!!
!!!