Chapter 37 Work, Power & Energy

The word energy comes from the Greek word energeia

Objectives

In this section, you will learn:

The definition of work and its units, how to calculate work done.Definition of power, its units and how to do calculations involving power.The definitions and units of energy. The different forms of energy. The principle of the conservation of energy. The sources of energy. About renewable and non-renewable energy sources.Conservation of energy Energy conversions and experiments to demonstrate Methods of saving energy

Energy is the ability to do _______ or move something.

What is energy?

work

Work is done when a force moves an object.

Work done = force x distance

A body that has energy is able to do work.

Energy is measured in Joules.

For example, a person needs 1000 Joules of energy to walk up the stairs.

We get this energy from respiration(i.e. using oxygen to release energy from food).

JouleJames Prescott Joule (1818-1899) was an English

brewer whose hobby was physics. His name was given to a unit of energy, the joule, and to a law showing

how much heat is developed by a given electric

current in a circuit.

There are many different forms of energy.

Can you name some?

Forms of Energy

Energy can exist in many different forms:

Two main groups:A. Stored energyB. Energy in action

A. Stored Energy

1. Potential Energy = stored energy. Example: the stored energy that water has behind a dam or energy stored in stretched elastic bands.

3. Nuclear Energy

2. Kinetic Energy – energy in moving objects.

e.g. a car travelling along a road has kinetic energy.

The nucleus at the centre of an atom has an enormous supply of stored energy.Nuclear energy is released in nuclear reactors and nuclear bombs

4. Chemical Energy

Chemical Energy is stored in oil, gas or other fuels. It is also stored in food.

Battery FoodCoal Oil

B. Energy in Action

1. Kinetic Energy = Energy associated with all moving objects

2. Heat Energy

The hotter the water particles in a boiling kettle the faster they move around

3. Light Energy

Light Energy travels in waves and is an important source of energy for our planet.

4. Sound Energy

Sound Energy is caused by vibrations.

Electrical Energy

Electrical energy comes from moving charges. It is easily changed to other forms of energy e.g. electrical energy to light energy in a lamp

Magnetic Energy

Magnetic energy is the ability of certain substances to attract or repel other

substances

Now, in your copy write down all the different forms of energy that you can remember…….

1. Energy is the ability to do___________.

Review Questions

2. What unit is energy measured in?

HINT

HINT

Can energy be destroyed?

Question to think about!

Conserving Energy

Energy is expensive to make and some sources are limited. It makes sense to conserve energy by:

Insulating buildings.Turning off energy sources, e.g. lights and electronic equipment, when not needed.Recycling materials.

Principle of Conservation of Energy

States that:Energy is neither created nor destroyed but can

be converted from one form to another.

Energy comes in many forms and can be converted from one form to another.

Example of Conservation of Energy

In a light bulb only 5% of electrical energy appears as light.

The remaining energy is turned into heat energy. The heat energy is lost by the light bulb.

Review

1. What is Energy?2. Name two types of stored energy?3. Name two types of energy in action?4. What word is used to describe the energy

associated with moving objects?5. What is the principle of conservation of

energy?

Answers:

1. What is Energy?Energy is the ability to do work or move

something.2. Name two types of stored energy?Potential energy, chemical energy, nuclear

energy3. Name two types of energy in action?

Kinetic energy, heat energy, light energy, sound energy, electrical energy, magnetic energy

Answers:

4. What word is used to describe the energy associated with moving objects? Kinetic energy

5. What is the principle of conservation of energy? Energy cannot be created or destroyed but it can change from one form to another.

Objectives of lesson

1. Investigate some sources of energy on the planet

2. Discuss Ireland’s energy needs3. Investigate which energy source is best to

use4. Consider ways to conserve energy in our

home and school.5. Carry out an experiment to show

chemical energy changing to electrical energy to heat energy

Sources of Energy

1. The SunPrimary source of energy on planeta) Green plants need the sun for photosynthesis.b) Heat from the sun keeps us warm

Solar panels and solar cells can trap the suns energy and turn it to heat and electricity

2. Fossil Fuels

Remains of dead plants and animals get squashed and these turn into peat, coal, oil and gas. These substances are called fossil fuels.

In Ireland we mainly use peat, gas, coal and oil to make electricity.

Fossil Fuels

Fossil Fuels are non-renewable sources of

energy

3. Renewable Energy Sources

Renewable sources of energy are those that will never be used up.

•Usually does not produce harmful waste products (exception nuclear energy).

•Expensive to set up.

Renewable and non-renewable energy Renewable and non-renewable energy sourcessourcesRenewable sources will last almost forever, non-renewable sources will run

out.

Even with renewable sources, there can be disadvantages, such as the

dangerous waste of nuclear energy.

Non-renewable sources

Renewable sources

Oil Wind

Coal Solar

Gas Nuclear

Turf Biomass and geothermal

4. Nuclear Energy

Nuclear energy is released by splitting up a large nucleus into two parts in a nuclear reactor. 1kg of uranium can produce as much energy as 3,000,000kg of coal.

Nuclear Energy

No nuclear energy in IrelandClosest nuclear plant is in Sellafield in the UK

Problems with Nuclear Energy

Radioactive substances are produced by splitting the atom. Disposal of these substances is dangerous and expensive

Radiation can damage living cells and cause cancers.

Nuclear FusionNuclear fusion is another method of producing energy from a nucleus.

Light nuclei are forced to join together producing a fuel called deuterium which is a form of hydrogen. The advantages would be a cheap, clean and endless supply of fuel

5. Other Sources of Energy

HydrogenFuel cells which turn hydrogen into electricity are used in things like space travel.

Energy Sources Advantages and Disadvantages

See text book pg 295-298Select two energy sources and write out their original source, one advantage and one disadvantage

Which Energy Source is best?

Different sources of energy suit different areas in the world e.g. In hot countries solar power stations are worth building

Conserving Energy

Make a list of 3 ways you could conserve energy in your home

Conserving Energy in your home

1. Put lagging jackets on hot water tanks2. Insulate attics with polystyrene or fibre

glass3. Double glaze windows

Energy Conversions

Some examples of energy conversions:

In a battery: Chemical energy→electrical energy→light energy

and heat energy

In a solar panel connected to a fan: Light energy→electrical energy→kinetic energy

Mandatory Experiment a) To show chemical energy changing to electrical energy to heat energy t/b pg. 299

Apparatus: Battery, beaker, coil of nicrome wire, connecting wires, cold water, temperature sensor and data logging equipmentSafety:Method:1.Place the resistant wire under the cold water in the beaker

2. Connect the resistance wire to the battery as shown in the diagram.3. Place the temperature sensor in the cold water and note the temperature after a few minutes.4. Turn on the switch and note the temperature of the water every 2 minutes using the temperature sensor.5. Record your results.

What is the energy conversion shown in this experiment?

Result of experiment:

Energy Conversion:Chemical Energy -> Electrical Energy -> Heat Energy

Result: The temperature of the water rises as long as the battery is supplying energy.

Conclusion:The chemical energy of the battery was changed to electrical energy in the circuit. The electrical energy in the resistant wire was changed to heat energy and this heat energy raised the temperature of the water

Experiment:

To show electrical energy changing to magnetic energy to kinetic energy p.g. 300

Apparatus: long nail, length of insulated wire, power supply, paper clips

Safety:Method:1.Wind the insulated wire closely around the nail2.Connect the two ends of the wire to a power supply3.Place some loose paper clips under the nail.4.Switch on the current and see what happens5.Switch off the current and notice what happens

Result:

Energy Conversion:

Conclusion:

Result: When the current flows the paper clips are attracted to the nail and insulated wire. When the current is switched off the paperclips are not attracted to the nail and insulated wire.

Energy Conversion:Electrical energy -> magnetic energy -> kinetic energy

Conclusion:The electrical energy from the power supply changes to magnetic energy in the nail. The magnetic energy in the nail causes the paper clips to move towards the nail. (The kinetic energy of the paperclips is changed to potential energy)

Experiment: To show light energy changing to electric energy to kinetic energy

Apparatus: solar cell, electric motor, light source e.g. lamp, connecting wires.

Safety:Method:1.Connect the solar cell to a miniature electric motor2.Place the solar cell in the path of light from a lamp and note what happens3.Block the light shining on the solar cell and note what happensResult:

Result:When the light from the lamp shines on the solar cell it makes the fan on the solar cell move. When no light shines on the solar cell the fan stops moving.

Energy Conversion:

Conclusion:

Energy Conversion:Electrical energy -> light energy -> electrical energy -> kinetic energy

Conclusion:

Electrical energy is changed to light energy in the lamp and then to electrical energy in the solar cell. The electrical energy is changed to kinetic energy when the fan moves on the solar cell.

Review of Energy (Fill in the blanks)

1. Energy is the ________________________________________2. The unit of energy is J_________3. The Principle of Conservation of Energy states

that_________ can neither be _________ or _________ but can from one form to another

4. Types of stored energy include: P____________, C _________and nuclear energy5. Types of energy in action include: K___________, H_________

and L____________6. Potential Energy is ___________________________________7. Kinetic Energy is ________________________________________8. Name two renewable sources of energy? 9. Name two non-renewable sources of energy?10. List two ways you can conserve energy at home?11. List two ways you can conserve energy in school?