Heat

Chapter 44 Page 296

Brainstorm!

What can you tell me about heat?

Heat

Heat is a form of energy

Heat can be measure in Joules (J) because it is a from of energy

What does energy do to an object?Heat can make things move

Where is the heat travelling in these pictures?

Heat Travels

Heat will always move from a hot object to a cold object until both objects are the same

temperature

This can be done in 3 ways:1. Conduction2. Convection3. Radiation

1. Conduction

Conduction is the transfer of heat through a solid without the particles in the solid moving

out of position

Conduction (only occurs in solids)

• Hot particles vibrate a lot

• Cool particles vibrate a little

Conduction

• Fast-moving particle (lots of energy) collide with neighbouring particles

• This gives them more energy, making them vibrate faster

Conduction

• This continues along the length of the solid until all the particles are vibrating with lots of energy

Conductors

Metals are good conductors of heat

They allow heat to travel through

Insulators

An insulator is a substance which does not allow heat to pass through it easily

Can you name any examples?

They are measured using tog value, where have you heard this before?

Insulators

Insulators

Why do you think insulation is important?

HomeworkDesign your own experiment

Today we will…

• Conduct our insulation experiment

• Look at method 2 of heat transfer : Convection

How are we going to conduct our experiment?

Which will be the best insulator?

News Paper?

Tea Towel?

Cotton Wool?

2. Convection

Have you ever heard of this term before?

Convection oven?Do you know how it works?

Convection is the transfer of heat through a liquid or gas when the molecules of the liquid or

gas move upward and carry the heat

To show convection in a liquid

To show Convection in a gas

Homework

Question 3 Page 304

Today we will…

1. Correct Homework

2. Recap

3. Radiation as a method of heat transfer

4. Expansion and Contraction1. Solid2. Liquid3. Gas

3. Radiation

Radiation is the transfer of heat in rays, from a hot object, without needing a medium to pass through

All hot objects radiate heat

This is how heat form the sun reaches the earth. It cannot travel by conduction or convection because of the empty space

Radiation

The hotter an object is, the more heat it will radiate

The heat radiated from an object also depends on the type of surface it has

A dull black surface, radiates heat out better than a bright, shiny surface

A dull black surface will also absorb heat better than a bright, shiny surface

To show heat transfer by Radiation

Radiation

Recap

Expansion and Contraction

Why do we need to take the lid off a container before we heat Chinese leftovers in the microwave?

Why does our deodorant can warn us to keep it away from direct heat?

How do we make popcorn pop?

Expansion and Contraction

Solids, liquids and gasses all expand when they are heated and contract when they are cooled.

When atoms are heated, they vibrate/ jiggle, much faster and need to take up more space

To show the expansion of a solid

Where can we see this at work?

The Bimetallic StripConsists of a plate of iron and copper fixed together

When heated copper expands more than the iron and so the bar bends. When it cools the bar straightens again

Why is this useful?

They are mainly used to switch on and off an electric current

It is used in simple fire alarms and any thermostat

To Show the expansion of liquids

Can a liquid also expand when cooled?

Water is a special case

Read about it on page 299 of book

To show the expansion of gasses

Conclusion

Solids, liquids and gasses all expand when heated and contract when cooled

Homework

Test on chapter of Heat next week!