1. Conservation of Energy
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Conservation of Energy
2016 EdExcel GCSE Physics
Topic 3
W Richards
The Weald School

2. Gravitational potential
The 9 types of energy
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Type
3 example sources
Type
3 example sources
Heat
Kinetic (movement)
Nuclear
Sound
Light
Chemical
Electrical
Gravitational potential
Elastic potential

3. Gravitational Potential Energy
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To work out how much gravitational potential energy (GPE) an object gains when it is lifted up we would use the simple equation…
GPE = mass x grav. field strength x Change in height
(Joules) (newtons) (N/Kg) (metres)
GPE H mg
You need to learn this equation!!

4. Some example questions…
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How much gravitational potential energy have the following objects gained?:
A brick of mass 1kg lifted to the top of a house (10m),
A 1,000kg car lifted by a ramp up to a height of 2m,
A 70kg person lifted up 50cm by a friend.
How much GPE have the following objects lost?:
A 0.2kg football dropping out of the air after being kicked up 30m,
A 0.05kg egg falling 10m out of a bird nest,
A 1,000kg car falling off its 200cm ramp.
100J
20KJ
350J
60J 5J
20KJ

5. Kinetic energy KE = ½ mv2 Kinetic energy = ½ x mass x speed squared
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Any object that moves will have kinetic energy.
The amount of kinetic energy an object has can be found using the formula:
Kinetic energy = ½ x mass x speed squared
in J in kg in m/s
KE = ½ mv2
You need to learn this equation!!

6. Example questions
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Lydia drives her car at a speed of 30m/s. If the combined mass of her and the car is 1000kg what is her kinetic energy?
Sam rides her bike at a speed of 10m/s. If the combined mass of Sam and her bike is 80kg what is her kinetic energy?
Josh is trying to catch a bus and is running at 3m/s. If he has a mass of 60kg how much kinetic energy does he have?
A 2000kg car is being driven at a speed of 10m/s. If it doubles its speed to 20m/s what happens to the car’s kinetic energy?
450,000J
4000J
270m/s
Increases from 100,000J to 400,000J

7. Example questions (higher)
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Steve is running away from the police and has 100J of kinetic energy. If he is running at 2m/s what is his mass?
James is driving in his car and has a combined mass of 1200kg. If he has 540KJ of kinetic energy what speed is he driving at?
Dave is running and has a kinetic energy of 750J. If his mass is 60kg how fast is he running?
Stuart is spotted walking around Tescos. If he has a kinetic energy of 150J and he’s walking at a pace of 2m/s what is his mass?
50kg
30m/s
5m/s
75kg

8. The Laws of Physics
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There are many laws of physics, but one of the most important ones is:
Energy cannot be created or destroyed, it can only be converted from one form to another

9. Electricity Light + heat
Energy changes
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To describe an energy change for a light bulb we need to do 3 steps:
1) Write down the starting energy:
3) Write down what energy types are given out:
2) Draw an arrow
Electricity Light + heat
What are the energy changes for the following…?
An electric fire
A rock about to drop
An arrow about to be fired

10. An example energy change - A skydiver
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An example energy change - A skydiver
Here’s a skydiver:
If the skydiver has reached terminal speed explain what happens to his…
Kinetic energy
Gravitational potential energy
…while he is falling.

11. Example energy change 2 - Elastic Potential Energy
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Example energy change 2 - Elastic Potential Energy
Elastic potential energy is the energy stored in a system when work is done to change its shape, e.g:
Describe the energy changes when the mass is:
At the top of it’s movement
In the middle
At the bottom

12. Energy Transfer Examples
Look at the following objects and write down what their energy changes are:
a) Electric Light Bulb
b) Battery
c) Hairdryer
d) Candle Burning
e) Model Car (Wind-up)
f) Dynamo
g) Yo-Yo
h) Radio
i) Kettle
j) Dropping a Golf Ball

13. Energy Transfer Diagrams
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Here’s a way to illustrate the energy changes of a device (let’s say a TV for example):
Light (80J)
Electrical
Energy (200J)
Sound (40J)
Heat (?)
Draw energy transfer diagrams for:
A light bulb
A hairdryer
A burning candle

14. Conservation of Energy
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In any energy change there is ALWAYS some “waste” energy:
e.g. a light bulb:
Electricity Light heat
In this example HEAT is wasted and it is transferred to the surroundings, becoming very difficult to use.
Describe the following energy changes and state the “waste” energy or energies:
A vacuum cleaner
A TV
A dynamo/generator

15. Which bulb is wasted the most heat energy?
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Which bulb is wasted the most heat energy?

16. Examples of wasted energy
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Clearly, not all of the energy from the fuel put into this car will become movement energy. Where is energy wasted in this car?
The bulb on the left is an “energy efficient” one. Why is the bulb on the right wasting energy?

17. Ways to reduce heat loss
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Q. How would you reduce energy loss in these objects?

18. Heat loss through walls
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I’m worried about how much heat I’m losing through my walls. What can I do to reduce this?
Here’s a new building with cavity wall insulation being installed:
How does the use of cavity wall insulation help keep a building warmer?
The rate of heat loss through a wall depends on two things:
How thick the wall is
The thermal conductivity of the wall

19. You need to learn this equation!!
Efficiency
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Efficiency is a measure of how much USEFUL energy you get out of an object from the energy you put INTO it.
For example, consider a TV:
Light (80J)
Electrical
Energy (200J)
Sound (40J)
Heat (?)
Efficiency = Useful energy out
Energy in
x100%
You need to learn this equation!!

20. Some examples of efficiency…
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5000J of electrical energy are put into a motor. The motor converts this into 100J of movement energy. How efficient is it?
A laptop can convert 400J of electrical energy into 240J of light and sound. What is its efficiency? Where does the rest of the energy go?
A steam engine is 50% efficient. If it delivers 20,000J of movement energy how much chemical energy was put into it? 2%
60%, given out to the surroundings as heat
40,000J

21. Increasing Efficiency (HT only)
Earlier on in this unit we considered these energy changes. How could we increase the efficiency of these devices?
a) Electric Light Bulb
b) Battery
c) Hairdryer
d) Candle Burning
e) Model Car (Wind-up)
f) Dynamo
g) Yo-Yo
h) Radio
i) Kettle
j) Dropping a Golf Ball

22. Fuels
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A “fuel” is something that can be burned to release heat and light energy. The main examples are:
Coal, oil and gas are called “fossil fuels”. In other words, they were made from fossils.

23. Renewable and non-renewable sources
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A ___________ energy source is one that when it has been used it is gone forever. The main examples are ____, oil and gas (which are called ______ ____, as they are made from fossils), and nuclear fuel, which is non-renewable but NOT a fossil fuel.
A renewable energy source is clearly one that can be _______ (“renew = make again” or “replenish”), e.g. _____, solar power etc.
Words – non-renewable, coal, fossil fuels, wood, renewed
Q. What do we use energy sources for? Why do we need them?

24. The problem with fossil fuels…
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25. Pollution
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When a fuel is burned the two main waste products are _____ dioxide and ________ dioxide.
Carbon dioxide is a _________ ___ and helps cause _______ _________. This is produced when any fossil fuels are burned.
Sulphur dioxide, when dissolved in ________, causes ______ _____. This is mainly a problem for ___ power stations.
Nuclear power stations do not produce these pollutants because they don’t ____ fossil fuels.
Words – sulphur, coal, global warming, carbon, acid rain, greenhouse gas, rainwater, burn

26. Non-renewable energy sources
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Advantages
Disadvantages
Cheap fuel costs
Pollution – CO2 leads to global warming and SO2 leads to acid rain
Good for “basic demand”
Coal, oil, gas and nuclear
Reliable
Nuclear produces little pollution
Fuel will run out

27. Renewable Sources of Energy- Biomass
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Renewable Sources of Energy- Biomass

28. 03/08/2019
Wind Power

29. Tidal Power
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High tide
Low tide

30. Wave Power
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31. Hydroelectric Power
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32. Solar Panels and Thermal Towers
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Solar Panels and Thermal Towers

33. Geothermal Energy
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34. Renewable energy sources summary
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Advantages
Disadvantages
Zero fuel costs
Unreliable (except for hydroelectric)
Don’t produce pollution
Wind, tidal, hydroelectric and solar
Expensive to build
Can be replenished/ won’t run out
May involve damaging the local environment
Solar is good for remote locations (e.g. satellites)

35. Energy Supply in the UK
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What conclusions can you draw from the following information?
What good or bad points can you draw from this information?