1.7 Energy, Work and Power

1.7.1 Energy

Core
• Identify changes in kinetic, gravitational potential, chemical, elastic (strain), nuclear and internal energy that have occurred as a result of an event or process
• Recognise that energy is transferred during events and processes, including examples of transfer by forces (mechanical working), by electrical currents (electrical working), by heating and by waves

• Apply the principle of conservation of energy to simple examples

ENERGY: The ability to do work or change matter

Task 1: Divide the cards into those that show types of energy and those that do not.

TYPES OF ENERGY
  1. LIGHT ENERGY: Energy of electromagnetic radiation. It travels in vacuum at the speed of 300,000,000 m/s.
  2. CHEMICAL ENERGY: Energy that is stored in the chemical bonds in molecules.
  3. INTERNAL ENERGY: The energy stored in a (hot) object.
  4. HEAT(Thermal) ENERGY: Energy associated with the movement of atoms or molecules that can be transferred.
  5. KINETIC ENERGY: The energy that an object in motion has because of its motion.
  6. POTENTIAL ENERGY: Energy stored within a physical system that has the potential to do work.
  7. GRAVITATIONAL POTENTIAL ENERGY: Energy an object has a result of its position in a gravitational field.
  8. ELASTIC ENERGY: Potential energy stored as a result of deformation of an elastic object, such as the stretching of a spring.

cf) FUEL: Material that releases energy as it changes chemically.
Task 1: In your notebook, group each type of energy given below into energy stored or energy from movement.
Energy stores
Energy transfers
Kinetic energy
Electrical energy
Gravitational potential energy
Thermal energy
Chemical energy
Light energy
Nuclear energy
Sound energy
Strain energy

Internal energy

Task 2: Play a game of hangman guessing the words listed above, to recap the types of energy.

Energy 101 Wind energy from youtube.com

PRINCIPLE OF CONSERVATION OF ENERGY: Energy is never created nor destroyed. It just changes from one form to another.
In any energy conversion, the total amount of energy before and after the conversion is constant.
Supplement
• Recall and use the expressions kinetic energy = ½mv 2 and change in gravitational potential energy = mg∆h
• Apply the principle of conservation of energy to examples involving multiple stages
• Explain that in any event or process the energy tends to become more spread out among the objects and surroundings (dissipated)
Q1. How much gravitational potential energy is gained if you climb a flight of stairs? Assume that you have a mass of 52 kg and that the height you lift yourself is 2.5m.

Q2. How much gravitational potential energy is lost by an aircraft of mass 80,000kg if it descends from an altitude of 10,000m to an altitude of 1,000m? What happens to this energy if the pilot keeps the speed of the plane constant?

Q3. Calculate the change in kinetic energy of a ball of mass 200g when it bounces. Assume that it hits the ground with a speed of 15.8m/s and leaves it at 12.2 m/s.

Q4. Calculate the gravitational potential energy of a high diver if she has a mass of 45kg and her centre of gravity is 5.0m above the water. Assuming that all her gravitational potential energy becomes kinetic energy during the dive calculate her velocity as she enters the water.


Natural resources: Any materials found on Earth that are used by humans

Energy resources: Any resources that release energy, especially resources/materials that humans use to generate electrical energy.

cf) FUEL: Material that releases energy as it changes chemically. ex) coal, oil, wood, gas, charcoal, methane, petrol


Fossil fuels

Activity 1: coal, oil and gas formation
List the fuels on your notebook and write where each one comes from.
Fuel where it comes from
wood: from trees
alcohol: fermented from plant material
manure: from animals that eat food
charcoal: from wood that is partially burned in a limited air supply
biogas methane: produced from things which grow
Notes to take:
All the above fuels store energy from the Sun via photosynthesis.
coal formed from forests in the Carboniferous period 300 million years ago
oil and gas formed over millions of years from small organisms at the bottom of the sea

The Carbon cycle

The Carbon Cycle or The Circle of Life by Melissa Landeen from youtube.com

* Use words from the list to complete the passage. You can use each word more than once.

Sun, conduction, convection, conservation, cooler, current, evaporation, fossil fuels, generated, heat, iron, light, non renewable, particles, radiation, renewable

Most of the Earth's energy comes from the Sun. Resources such as coal, oil and gas, which have stored energy over millions of years are called fossil fuels which are non renewable as they cannot be replenished within the Earth's lifetime. Food, wind and waves are renewable resources: they will never run out.

Electricity is generated from both types of resource, but most of our electricity comes from burning fossil fuels. Energy from electricity is transferred to movement, heat and light in the appliances we use at home and at work.

There is a constant transfer of energy from hot objects to cooler ones. Energy transfer from particle to particle is called conduction . Energy transfer by the upward and downward movement of fluids is called convection. Liquids and other objects containing moisture lose energy by evaporation .

Energy from the Sun travels to the Earth as radiation. All objects lose and gain energy by this method. It is the only way in which energy is transferred that does not involve the movement of particles .

When energy is transferred, there is no gain or loss of energy. This is known as energy conservation. It does become more spread out, which makes it difficult to recover.

Problem solving from Harcourt Education Ltd 2003 Catalyst 1

This picture shows a new youth centre which is to be built in the town. In order to get planning permission, the site must be run as an environmentally friendly development. This means that fossil fuels cannot be used to supply any of the energy needed in the centre.
The energy needs for the centre will include activities to entertain young people. There will be a kitchen to provide meals, workshops for practical hobbies, a disco and a television room. Think about how the energy for this new centre could be supplied without using fossil fuels.
external image file.cfm?2FD001223C46394D

Take notes on;
  1. Why are some energy resources described as ‘renewables’ and others as ‘non-renewables’?
  2. Write some simple statements explaining the difference between these two terms.

1.7.2 Energy resources


• Distinguish between renewable and non-renewable sources of energy

What is the source of most of Earth's energy?

Energy resources can be either renewable or non-renewable.
Non-renewable resources: The resources are used faster than they can be replaced, so the supply is limited. Example) Sun, water, wind, biomass and geothermal
Renewable resources: The resources will not run out because they are replaced as quickly as they are used. Example) Fossil fuels- coal, oil and natural gases

Renewable vs non-renewable energy resources from ck12.org

• Give advantages and disadvantages of each method in terms of cost, reliability, scale and environmental impact
• Describe how electricity or other useful forms of energy may be obtained from:
– chemical energy stored in fuel
– water, including the energy stored in waves, in tides, and in water behind hydroelectric dams
– geothermal resources
nuclear fission from cyberphysics.co.uk
– heat and light from the Sun (solar cells and panels)
– wind
Supplement
• Understand that the Sun is the source of energy for all our energy resources except geothermal, nuclear and tidal
• Show an understanding that energy is released by nuclear fusion in the Sun


Task 1
Your task is to answer the three big questions below. In order to answer the questions, you will need to do some research and read about the following issues first.
Find out about as many energy resources as possible. Draw up a chart showing these resources divided into renewables and non-renewables.
At present, most of the energy used in the world is from non-renewable sources. What makes these so attractive and useful? What problems arise from our use of non-renewables?
How can using renewables avoid these problems? Why have developed, industrial nations been so slow in using renewables?
Think of a simple, bold way of presenting your answers to these three big questions – perhaps as a poster or as a slide-show.
Big questions
  1. Why are some energy resources described as ‘renewables’ and others as ‘non-renewables’? Write some simple statements explaining the difference between these two terms.
  2. Why should we make more use of renewables?
  3. What problems are there with the use of renewables?

Task 2
Moja Island Project
Your task is to make a plan for a world that does not rely on fossil fuels for most of its energy.
During the class, you will research on renewable energy resources and make a decision as a group on what energy resources you will use in Moja island. Then, you will construct a poster as a group based on your chosen energy resources in Moja island. Describe each step of the process on how to generate electricity and label them for your chosen power station. As a group, you will present your choice of renewable energy resources and write a short report which is to be sent to a Scientific Magazine based on your in class research. Discuss advantages and disadvantages of using your chosen energy resources. Final report to be submitted through ManageBac and bring your hard copy to class next week.
  1. What different activities do we use energy resources for?
  2. Think about each of the following areas and decide which are essential. Are there any where we could reduce our consumption of energy?
  • industry (for example, manufacturing, chemicals, metals)
  • transport (for example, road, rail, sea, air)
  • commerce (for example, business, banking, government, entertainment)
  • domestic (for example, heating, lighting, washing, entertainment)
How can we supply the energy needed for essential activities? Try to make a realistic appraisal of our energy needs and how we can supply them. Would different parts of the world make use of different energy resources?

Energy Project Marking Criteria
Is your project
4. Great
3. Good
2. Need an improvement
1. Does not meet up basic requirements
*Examiner's Comments or Suggestions
an intellectual story? or 
sensational?





mentioning all the major problems?explaining advantages of energy resource(s) clearly?





explaining advantages of energy resource(s) clearly?





suggesting a good solution to the problems?





including detailed diagrams or artwork?
using ICT to produce an illustrated project? eye catching?





Total mark out of 20




/ 20
Nuclear Energy
Describe how electricity or other useful forms of energy may be obtained from: nuclear fission
• Give advantages and disadvantages of each method in terms of renewability, cost, reliability, scale and environmental impact
• Show a qualitative understanding of efficiency
efficiency =
useful power output × 100%
energy input
  • What are Nuclear Accidents
  • How are they Classified
  • The Dangers Associated with them
  • How to prepare for and protect from nuclear accidents
  • How to determine your RISK LEVEL of them

Nuclear fission

Natural uranium is a dense radioactive metal. It is mostly made up of two isotopes: uranium-238(over 99%) and uranium-235(less than 1%).
The nucleus becomes highly unstable and splits into two lighter nuclei, shooting out two or three neutrons as it does so. The splitting is called fission. It releases energy which throws the bit apart.
nuclear fission from cyberphysics.co.uk

Opinions on nuclear power
The following quotes show some peoples’ opinions on whether we should build more nuclear power stations in the UK.
Colour code them to show which are quotes for the building of more nuclear power stations and which are against.



Understanding Nuclear power plants total station black out from youtube.com

Is nuclear power safe? BBC Documentary from youtube.com

How does a Nuclear Power Plant work?
Nuclear Fission
Click to Run

Phet Nuclear Fission simulator from University of Colorado
external image Nuclear-Power-Plant-Diagram-Optimized-2.jpg
Image from https://upload.wikimedia.org/wikipedia/commons/c/c3/PWR_nuclear_power_plant_diagram.svg


Inside a Japanese power station from youtube.com



Do we need Nuclear Power?


Describe advantages and disadvantages of using Nuclear Power. You must include the basics of "How a Nuclear Reactor Works" and the dangers of an accident at a nuclear plant such as the handling of nuclear material, the operating of the plant and disposal of the nuclear waste. Lists of bullet points are acceptable. You will be given one period to write your opinions within 500 ~ 800 words.
Nuclear Power – Research

Your assessed task for this unit will be to write a newspaper article about nuclear power. THIS WILL BE WRITTEN UP IN CLASS
Your homework is to do some research to prepare for this task.
You need to find and PRINT OUT, COPY or MAKE NOTES ON at least three sources.
You must bring your research to the lesson – YOU WILL NOT BE ALLOWED TO LEAVE THE LESSON TO GO AND PRINT THINGS. You MAY annotate, highlight, underline, add Post-IT notes, etc to your research. You will be allowed to use this in the lesson. Your research must be handed in at the end of the lesson.
You may stick graphs and/or pictures into your final article.
What do I need to do? The table below outlines what you should aim to include in your article – you should bear this in mind when doing your research.

What you should do
Check
Must
State some ways in which our choices about energy affect us

State a conclusion

State some evidence for and against your conclusion

Identify which evidence supports your conclusion.

and which does not support.

Describe some negative and positive consequences of adopting nuclear power

Should
Identify questions about nuclear power (or alternative forms of power) which science can answer

Identify some moral questions about our choice of power source

Identify different ways in which people are affected by nuclear power (and/or other forms of power)

Describe some of the evidence which supports or refutes an argument about nuclear power, e.g.
- Nuclear power is safer than coal
- Nuclear power is more reliable than renewable
- Nuclear power is dangerous
- Nuclear power is not needed

Explain how our choices about which power sources we use affect society,

and why different societies/groups may make different decisions. (e.g. compare Norway, England and Egypt)

Could
Explain some of the evidence which supports or refutes an argument about nuclear power

Distinguish between statements of fact and statements of opinion

Explain some of the evidence which has changed our ideas about nuclear power and/or coal power, renewable resources etc..

Evaluate the reliability/validity of the facts and opinions for and against your conclusion

Explain some of the unintended consequences of a particular choice of power source

Explain how changing sources of power has changed/will change society


This homework must be completed by:
4th October 2016
Nuclear Power Report Mark Sheet

Nuclear Energy Pros and Cons

Energy releases

In a chemical change such as burning, atoms get arranged. Energy is released as electrons settle into different positions in atoms.
In radioactive decay, nuclear particles get rearranged. The energy released per atom is around a million times greater than that from a chemical change such as burning.
In fission, lots more atoms are involved every second than in natural decay. Energy is released much more rapidly.
Supplement
• Show an understanding that energy is released by nuclear fusion in the Sun
• Understand that the Sun is the source of energy for all our energy resources except geothermal, nuclear and tidal
Have you spotted the Earth in the solar system? Can you describe nuclear fusion?How does fusion power the Sun?


How close are we to nuclear fusion from forbes.com
What is nuclear fusion from www.iter.org

Challenge question
Describe what Nuclear Fusion is:

• Show a qualitative understanding of efficiency
• Recall and use the equation:
efficiency =
useful energy output × 100%
energy input
EFFICIENCY: Fraction of energy which is usefully transferred.The efficiency of an energy conversion is the fraction of the energy that ends up in the desired form.
Sankey diagram of a light bulb from skoool.co.uk

efficiency =
useful power output × 100%
power input





Device
Typical efficiency
Electrical heater
100 %
Large electric motor
90 %
Washing machine motor
70 %
Car petrol engine
30 %
What is the most common form of waste energy?
Thermal energy and Sound energy

Why is it important not to waste energy?
The reasons are that energy is expensive and it's supplies are often limited and our use of energy can damage the environment.

Task 3
Your task is to answer the the big question below. These questions are linked. In order to answer the questions, you will need to do some research and read about the following four factors in italic.

Could LEDs save a planet? from bbc.co.uk

1. Our need for light
2. 21st Century light
Video transcript: Custom film made for BBC iWonder, featuring Danielle George at the Royal Institution of Great Britain.
We take for granted how easy it is to switch on a light and pierce the gloom. The UN calls this a basic human right. But the technology most of us use dates back to the 1800s.
Worldwide, a fifth of all the electricity we generate is used for lighting. Now this gives us a hefty energy bill – but it also means we pump out three times more carbon dioxide than the entire aviation industry.
And the need for light is only going to get bigger, as our populations grow, modernise and move into cities.
Living in darkness isn’t an option. But there’s a development that could slash our energy consumption.
The traditional light bulb is actually a pretty hopeless way of making light. It takes loads of electricity to generate just a little bit of brightness.
LEDs or light emitting diodes have been around since the sixties but people are getting really excited about them now.
Breakthroughs in their design means that LEDs are real contenders to replace the wasteful filament bulbs in most places. And as LEDs use a fraction of the energy to create light, this simple electronic component could have a global effect.
3. How LEDs use quantum physics to shine?
How LEDs use quantum physics to shine
Animation transcript: Custom animation explaining how LEDs work made for BBC iWonder, narrated by Prof Danielle George.
PROF DANIELLE GEORGE:
For over a hundred years, we’ve lit up our homes with incandescent light bulbs that work in a pretty simple way.
An electrical current goes through a thin wire tightly coiled inside the glass bulb. The current makes the wire get very hot and glow. And that gives off the light, but it’s pretty inefficient. 90% of the energy is lost as heat.
LEDs make light in a completely different way – and they use the curious world of quantum mechanics to do it.
Inside an LED are two layers of special material made from semiconductors. One layer contains a lot of energetic electrons. The other layer is filled with holes – which are really broken chemical bonds between atoms.
When an LED is hooked up to a battery, the electrons and holes flood towards the place where the two layers of the semiconductor meet. As soon as an electron meets a hole in this region, it falls into it, and repairs that chemical bond. In a flash, it releases the energy that it was using to move about – as a bright light.
And that keeps happening, as the battery keeps pushing electrons and holes towards each other.
Because most of the energy goes into making light rather than heat, LEDs are super-efficient.
And as new types of semiconductors are being developed, scientists are rapidly improving the efficiency of LEDs. In a few years, LEDs on the high street could be 10 times more efficient as incandescent light bulbs of the same brightness.
4. Where do LEDs light up our lives today?
i) Home lighting
ii) Crop production
iii) Backlit screens
iv) Street lighting
v) Car lights

Uses
Home lighting
Crop production
Backlit screens
Street lighting
Car lights
Descriptions
We use roughly 20% of our electricity to light our homes, so making small changes to our lights could give big energy savings. Although most UK homes still use traditional incandescent filament bulbs, the sale of these for household use has been banned by the UK government in favour of low energy alternatives.
A 60W incandescent bulb can be replaced by a 12W ‘energy-saving’ CFL (compact fluorescent lamp) bulb or a 10W LED light. As LEDs continue to improve in construction and design, their efficiency could double, compared to CFLs, in just a few years. Along with savings in electricity bills, they last longer, can produce ‘warm’ or ‘cold’ light and, unlike CFLs, don’t contain toxic mercury.
However, LED lights are currently more expensive than other forms of domestic light. The home store Ikea reported that only around 5% of their light bulbs sold in 2013 were LEDs. But rising electricity costs and falling LED prices mean that more of us will be switching them on.
Most of the world’s crops are currently grown outdoors in sunlight. But some food producers are moving farming indoors to make crop production more efficient. This can improve yields throughout the year and reduce water and fertiliser use.
The cost of traditional fluorescent growing lights is high, so indoor farms are starting to use LEDs instead. This includes the world’s largest ‘plant factory’ in Japan, which uses 17,500 LEDs to harvest 10,000 heads of lettuce every day.
Along with significant energy savings, LEDs generate less heat so they can be placed closer to the plants, allowing more plants to be grown together in a tight space. Manufacturers are also trying to fine-tune the type of light emitted by the LEDs to maximise plant growth.
TVs and computer screens were among the first mass market uses of LEDs, in the 1990s. LCD screens brightened by LEDs generally use 20–30% less energy than those backlit by older CCFL (cold-cathode fluorescent lamp) technology. As LEDs are compact and lightweight, they’re ideal for this use. LEDs are used to backlight all handheld devices such as mobile phones and by 2016, all backlit screens will be illuminated by LEDs.
There are over 7 million street lights in the UK and nearly half of them are over 30 years old. Converting existing street lights to LEDs could cut energy consumption by more than 50% according to early trials.
It's not just energy savings; LED street lights produce directional white light rather than the yellow glow of traditional sodium lamps. This could be more aesthetically appealing and help to reduce light pollution across the skyline and into people’s homes.
The Upper Thames Street Tunnel in central London became the first UK tunnel lit with LEDs in 2011 and Tower Bridge was fitted with a new lighting system containing 1,800 LEDs ahead of the 2012 Olympic Games. By 2016, 35,000 LED street lights will be installed in London as part of the city’s plans to cut its carbon emissions, with other local authorities likely to follow this example.
LEDs are already commonly used in rear car lights, brake lights and interior displays. Their ability to be switched on almost immediately is a great advantage when reaction times are critical. LEDs are starting to be used in car headlights too, with one manufacturer predicting that 20% of headlights will incorporate LEDs worldwide by 2020.
A typical halogen headlight might use up to 65 watts of power. An equivalent LED headlight needs around 15 watts. LEDs need replacing less frequently because of their more durable design.
But there is one drawback; the low heat of LEDs mean headlamp lenses may be more likely to frost over on cold mornings.

1.7.3 Work
• Relate (without calculation) work done to the magnitude of a force and the distance moved in the direction of the force
• Demonstrate understanding that
work done = energy transferred
Supplement
• Recall and use ∆W=Fd=∆E

Work 1, Work 2, Work 3
from Khan academy

Work

Work is done when a force moves an object in the direction of the force. Work is a scalar quantity. The SI unit is the joules [ J ]

The transfer of energy to a body by the application of a force that moves the body in the direction of the force.
It is calculated as the product of the force and the distance through which the body moves.
Work = Force x Distance
1J = 1N x 1m


WORK DONE BY A NON-CONSTANT FORCE
Work done is the area under the force distance graph.


Gravitational potential energy = F x d = mgh
Kinetic Energy = F x d = ma x d = m(v-u)/t x [(v+u)/2] x t = (1/2) mv2

1.7.4 Power
• Relate (without calculation) power to work done and time taken, using appropriate examples

Supplement
• Recall and use the equation P =E/t in simple systems

POWER
The rate of doing work. Unit is the watt. 1W = 1J / s

Aim: To calculate the work done and power of a person going up a flight of stairs. This way we can find who the most powerful person in the room is.

Work done can be calculated by multiplying force times distance . In this case the force will be the weight of the person. The distance is always in the opposite direction of the force. We need to find the height climbed up 1 flight of stairs.
Finding the power
The power of the person depends on the amount of work they need to do to get up the stairs and how quickly they can do it.
Power = Work done / Time taken


Aim To find the most powerful person in class.

MethodFind the height from the top to the bottom of the stairs using a meter ruler.Measure the weight of each person in your group.Time how quickly each person takes to get up the stairs. Repeat this 3 times.
Result
Record all result in the table and find the average time.

Calculation
Using the equations above, work out the work done by each person in the group and the power of each person.
SHOW ALL YOUR WORKING!!!

Conclusion
Who is the most powerful? Who was the quickest? Are they the same? Does this surprise you?

Evaluation
To make a fair test, what would you consider?



Homework
Complete workbook from p.29 to p.33.

Do revision 1 to 5 and finish Test Bite from BBC GCSE Bitesize

Challenge
IB DP 2.3 WORK ENERGY POWER