Forces and Energy
Unit 3
Lesson
objectives
❑ To learn that energy cannot be created or destroyed.
❑ To understand that there is no increase and decrease in
energy as energy does not change.
❑ To understand that energy is dissipated from hotter place
to cooler place.
❑ To know what is Law of conservation of energy?
❑ To know about input energy and output energy
Key
words
temperature
Heat
dissipation
conserved
created
destroyed
system
thermal
Entry
Ticket!
What do you mean by average energy of the particle in an object?
Assess
yourself!
Look at the burning candle here
Assess
yourself!
You looked at the burning candle
❑ Where does the energy for the candle flame come from?
❑ In which form does candle wax store energy?
❑ What happens to the chemical energy stored by the candle wax as the candle
burns?
❑ What happens to the total energy in the room as the candle burns?
Energy
transfer
How the energy transferred, stored, wasted
Energy
transfer
Energy is conserved in a lamp
❑ When we say that energy is conserved, we mean that the total quantity of
energy stays the same. This happens when energy is stored, changed,
transferred or even dissipated.
❑ Look at the energy diagram for an electric lamp (extension material).
❑ The energy diagram shows that every time 100 J of electrical energy is
supplied to the lamp, 10 J of this is changed to light energy and 90 J is
changed to thermal energy. The light energy is useful, and the thermal
energy is wasted.
❑ The electrical energy is called the energy input and the light and thermal energy together are called the
energy output.
❑ The total energy input of 100 J is the same as the total energy output of 10 J + 90 J = 100 J.
❑ This shows how energy is conserved in an electric lamp.
the blocks can be transferred
between different stores, but they
are not created or destroyed.
Energy
transfer
Energy is conserved in a car
❑ The energy diagram for the engine in a car has more energy outputs
(extension material).
❑ In the energy diagram for a car engine, the energy input and outputs are
shown as percentages. Notice that the energy input is 100% and the total
energy output adds up to 100%. Once again, energy is conserved.
❑ In these examples, the electric lamp and the car engine are types of system.
In physics, a system is something that has been chosen to be studied,
especially in terms of energy changes
❑ The total energy output can never be greater than the total energy input in any type of system. This is
because energy cannot be created. Created means to make something, or to bring something into existence.
Energy
dissipation
Energy is dissipated in a car
❑ Wasted energy, such as thermal energy, is dissipated. Dissipated
means this energy spreads out into the surroundings and
becomes less useful.
❑ Although this energy is dissipated, it is not destroyed. Destroyed
is the opposite of created. Destroyed means to damage
something or to end its existence.
❑ The law of conservation of energy states that energy cannot be
created or destroyed, only changed or transferred.
Input and
output
Law of conservation of Energy
❑ When the required type of energy (input) is given to a device,
it is converted to desired or useful and waste energies (output)
❑ As energy is conserved so we can say that
input energy = output energy
❑ For the given example of hair dryer.
300J = 100J + 150J + 50J
300J = 300J
❑ The law of conservation of energy states that energy cannot be
created or destroyed, only changed or transferred or dissipated..
Energy
dissipation
Law of conservation of Energy
The law of conservation of energy states that
energy can neither be created nor
destroyed - only converted from one
form of energy to another.
Video
Energy is dissipated in a car
❑ Wasted energy, such as thermal energy, is dissipated. Dissipated
means this energy spreads out into the surroundings and
becomes less useful.
❑ Although this energy is dissipated, it is not destroyed. Destroyed
is the opposite of created. Destroyed means to damage
something or to end its existence.
❑ The law of conservation of energy states that energy cannot be
created or destroyed, only changed or transferred.
Exit
Ticket!
Write 3 main points they remember
through the lesson
Wrap up!
What is meant by dissipated energy?
What is the law of conversation of energy?
What is the difference between input and output energy?
Learner’s book answers
Answers