Heating & Cooling

Introduction to Heating & Cooling

Starter

Use the particle model to show what the particles of a solid, liquid and a gas look like:

Solid Liquid Gas

Learning Objectives

• Know that all objects absorb and emit heat energy

• Describe how particles move and transfer energy in solids, liquids and gases

• Explain the process of conduction

Particle Simulation

• http://phet.colorado.edu/en/simulation/states-of-matter

Heat Energy

Heat Energy

• Infra-red radiation• All objects absorb and emit heat energy

Kinetic theory

• Kinetic theory describes how particles move in solids liquids and gases

In your books– Explain how the movement of particles is different

in solids liquids and gases.– Discuss how materials change between the 3

states of matter

Methods of Heat Transfer

• Conduction

• Convection

• Radiation

Conduction

Conduction

• Type of thermal energy transfer which occurs in solids

• Vibrating particles pass on extra kinetic energy (or heat) to neighbouring particles.

• This eventually results in a rise in temperature at the other side of the solid.

Thermochromic paper

• Make a prediction as to which metal will be the best conductor and why

• Describe how thermochromic paper works• Explain why the different pieces of paper

changed colour at different rates• Explain the process of conduction• Which metal do you conclude was the best

conductor? Why?

Homework

• Outline what happens in conduction• Prediction & explanation• Method• Conclusion

Methods of Heat Transfer

Draw one of these and explain what is happening

Why do metals feel cold?

Metals have free electrons

StarterMatch the key words to the definitions and their

explanations (don’t copy it out!)

1) Conduction

2) Convection

3) Radiation3) Type of thermal energy transfer which occurs in

solids

1) Type of thermal energy transfer which occurs in

liquids and gases

2) Type of thermal energy transfer which does not

require matter in order to travel

1) Vibrating particles pass on extra kinetic energy (or heat) to

neighbouring particles. This eventually results in a rise in

temperature at the other side of the solid.

3) Liquid and gas particles are free to move. Particles with

more kinetic energy move from hotter regions to cooler regions, taking their thermal energy with

them.

2) Thermal energy travels as waves.

It travels at the speed of light.It can travel through a vacuum.

This is the only way heat can reach us from the sun.

Learning Objectives

• Understand how heat is transferred in liquids and gases

• Explain how heat can be transferred in terms of convection currents

• Apply your knowledge of the 3 methods of heat transfer to exam style questions

Convection• Type of thermal energy transfer which occurs

in liquids and gases

• Liquid and gas particles are free to move. • Particles with more kinetic energy move from

hotter regions to cooler regions, taking their thermal energy with them.

Convection Currents

• Hot air/liquid is less dense than cooler air/ liquid so it rises

• Cool air/liquid is more dense so it falls/sinks• The rising and falling of particles with

more/less thermal energy results in a convection current

• http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/energy/heatrev1.shtml

Radiation

• Method of heat transfer which does not require particles

• Heat energy travels as waves• This is how heat from the sun reaches Earth

Remember! Not all radiation is dangerous!

Exam style questions

Starter

• Here are 2 cubes of the same dimensions, made from the same material:

• If both cubes have a starting temperature of 100°C and are left on a cool surface, which cube will have cooled down the most after 10 minutes? Explain your answer.

Learning Objectives

• Know that all surfaces emit and absorb some thermal radiation

• Explain why surfaces emit and absorb radiation at different rates

• Predict the rate at which objects will cool compared to others based on their surfaces

• All objects absorb and emit some radiation• Some surfaces are better at this than others

Colour Finish Ability to absorb thermal radiation

Ability to emit thermal radiation

Dark Dull or matt Good GoodLight Shiny Poor Poor

Drawing tables

• Independent variable• Dependent variable

Drawing tablesIndependent Variable Dependent Variable

Time (min) Temperature of water (°C)Black

containerShiny

containerInsulated container

Bare metal container

0

5

10

15

20

25

30

Safety goggles

You will need:• 4 copper containers with different surfaces/coverings• 100ml boiling water in each

(use a glass beaker to carry the water!)• Thermometer• Watch with a second hand/stopwatch• Investigation sheet with results table• Graph paper

Condensation & Evaporation

• Starter: Exam style question

A wet towel is left on a radiator in a room turned on at 30°C. Another wet towel of the same size and material is hung on a washing line outside. The temperature is 15°C and there is a steady breeze. Which towel will dry the quickest and why?

Learning objectives

• Define what is meant by evaporation and condensation

• Explain how the 2 processes occur in terms of particles and kinetic energy

• Tackle some exam style questions on heat transfers

Evaporation & Condensation

Evaporation & Condensation

EvaporationProcess by which a liquid becomes a gas.Evaporation takes thermal energy away from the surface on

which it is occurring.Particles move further appart due to more kinetic energy

CondensationProcess by which a gas becomes a liquid.Particles move closer together as they have less kinetic energy

Insulation

Starter• What do we mean by insulation?• List as many ways as you can think of in which

we can insulate our homes

Learning objectives

• List some examples of how we could insulate our homes

• Explain how each of these methods reduces heat transfer and cuts energy costs

• Understand what is meant by a U-value

Cavity wall insulation

Cavity wall insulation

Cavity wall insulation

• Air is a poor conductor of heat.• Filling a wall cavity with fibreglass of

polystyrene traps pockets of air between the walls.

• This reduces heat transfer by conduction.

Double glazing

Double glazing

• An air gap is created• This reduces heat lossby conduction

Double glass bottle

Vacuum

Silvering

U-values

U-values

• A measure of heat loss.• The ‘overall heat transfer coefficient’• The lower the U-value, the better the insulation

provided by the material.

• The U-valure currently required for a new-build external wall is approx. 0.25.

You DO NOT need to know this for the exam

U-value = W/m² x k

Heat loss in square metres of roof/glass etc

When the temperature (k) is 1°C lower outside than inside

Questions

1. What does a U-value measure?2. Why would a U-value be relevant to someone living in a

warm climate?3. Give 2 advantages of using materials with a low

U-value in a building.4. Will a building that loses less energy have a low or a high

U-value?5. Describe the effect adding insulation to a building has on

its U-value and heat loss to the surroundings.

IN FULL SENTENCES PLEASE!

Payback Time

StarterLast lesson we talked about ways of insulating buildings.List as many ways of doing this as you can remember.

Learning Objectives

• Understand what is meant by the term ‘payback time’

• Start to tackle some exam-style calculations on payback time.

Effectiveness

Effectiveness

• The more effective a method of insulation, the better it is at conserving heat energy.

• What does this tell you about its U-value?

Payback Time

Payback Time

• The time taken to recoup an investment

Payback time = Cost of insulator ÷ annual fuel saving