1. Lesson link
What is efficiency?

2. Developing Explain what is meant by conservation of energy
Learning Objectives
Developing Explain what is meant by conservation of energy
Securing Analyse the changes involved in the way energy is stored when a system changes
Exceeding
Explain that where there are energy changes in a closed system, there is no net change in the energy of that system

3. Draw a line under last lesson’s work and write today’s title in your book...
20/11/2018
c/w
Work Done and Power

4. Recap quiz! Complete the following, working up the levels!
Equation Bank
Recap quiz! Complete the following, working up the levels!
KE= ½ x mass x velocity2
KE= ½ x m x v2 A B C
A= 30kg, B= 8kg, C= 2kg

5. KE= ½ x m x v2 When do objects have the most kinetic energy?
When an object is moving, it has kinetic energy. The faster it is going, the higher the energy!
KE= ½ x mass x velocity2
KE= ½ x m x v2
So the amount of the energy depends on two things:
The mass of the object
The velocity of the object
Mass is in kg
V is in m/s
KE is in J

6. So first let’s practice: How much kinetic energy would each of these objects have if they had these values of mass and velocity?
A 1200kg car travelling at 8m/s
38400J!
A 90kg bike travelling at 5m/s
1125J!
0J!
A 2100kg rocket which is stationary

7. What is the law of conservation of energy?
Lesson link
What is the law of conservation of energy?

8. It can only be transferred from one form to another.
Lesson link
The law of conservation of energy state that energy cannot be created nor destroyed.
It can only be transferred from one form to another.

9. The law of conservation of energy means that
Energy Transfer
The law of conservation of energy means that
“Energy is not created or destroyed, only TRANSFERRED or TRANSFORMED from one energy type to another”
This makes sense really, think of a tennis ball being picked up (gaining GPE) and then being dropped. As it’s dropping all that GPE is being transformed into kinetic (movement) energy!

10. Exam Practice
Susan drops a tennis ball and notices the following pattern when she takes a photo many times a second. Discuss the energy changes that are occurring as the tennis ball bounces in this way.
6 marks

11. Exam Corrections:
Susan drops a tennis ball and notices the following pattern when she takes a photo many times a second. Discuss the energy changes that are occurring as the tennis ball bounces in this way.
6 marks
Before the ball is dropped it has maximum GPE as it is high above the ground. As it’s released this GPE gets converted into KE as it falls. The kinetic energy increases as it nears the ground as it’s getting faster. Upon hitting the ground, this KE is then converted back into GPE (and again each time) as it rises above the ground. It’s getting less high each time because on each bounce it is transferring energy to surroundings as heat and sound

12. Engage
For the following slides you need to draw a small diagram of the system and underneath explain the energy transfers involved
System 1: A man pushes a boulder up a steep hill

13. Engage
For the following slides you need to draw a small diagram of the system and underneath explain the energy transfers involved
System 2: A car hits a wall

14. Engage
For the following slides you need to draw a small diagram of the system and underneath explain the energy transfers involved
System 3: A steam engine accelerating due to a constant force

15. Engage
For the following slides you need to draw a small diagram of the system and underneath explain the energy transfers involved
System 4: A motorbike slowing down

16. Engage
For the following slides you need to draw a small diagram of the system and underneath explain the energy transfers involved
System 5: A kettle boiling water

17. ‘Lost’ Energy What does the law of conservation of energy state?
Sometimes we might say some energy is ‘lost’. This isn’t particularly accurate however…
What does the law of conservation of energy state?
So what has actually happened to the ‘lost’ energy?
When a mechanical process is occurring (e.g. like a human running or a motor spinning), there is commonly a rise in temperature.
As such some of the energy provided (from the fuel) gets transferred into thermal/heat energy and sound!

18. Unwanted energy transfer
Here is a perfect example of a system that has unwanted energy transfer. Some of the energy provided by the petrol (total energy) is being dissipated as heat energy which is the wasted energy
The kinetic energy is what we actually want (to move the machine) so this is the useful energy
What could we do to this machine to make sure that we waste less energy as heat?

19. Time to practice… Complete all the questions on the sheet provided.
Make sure to write in full sentences.
E.g.
Question 1: State the law of conservation of energy
Answer: The law of conservation of energy is….

20. Exam Practice
1a) State the equation linking gravitational potential energy, mass, g and height.
(1 mark)
(iii) A motor lifts a 130 g mass to a height of 63 cm. Calculate the gravitational potential energy (GPE) gained by the 130 g mass. (2 marks)
(iv) Why is the amount of GPE gained by the mass less than the amount of electrical energy transferred to the motor? (2 marks)

21. Exam Corrections:
1a) State the equation linking gravitational potential energy, mass, g and height.
(1 mark)
GPE = mass x g x height [1 mark]
(iii) A motor lifts a 130 g mass to a height of 63 cm. Calculate the gravitational potential energy (GPE) gained by the 130 g mass. (2 marks)
130g = 0.13kg and 63cm= 0.63m [1 mark]
GPE= m x g x h GPE= 0.13 x 10 x 0.63m = 0.819J [1 mark]
(iv) Why might the amount of GPE gained by the mass be less than the amount of electrical energy transferred to the motor? (2 marks) ..
Some of the energy provided to the motor will be used to overcome friction leading so some energy being wasted as heat and sound

22. Developing Explain what is meant by conservation of energy
Learning Objectives
Developing Explain what is meant by conservation of energy
Securing Analyse the changes involved in the way energy is stored when a system changes
Exceeding
Explain that where there are energy changes in a closed system, there is no net change in the energy of that system

23. Independent Study
Research and report on the methods used by motor companies to increase fuel efficiency (reduce dissipation of energy as heat) since 1975