Grade 7 - Unit C

What are some things that keep us warm?

What are some items that cool us down?

Heating and Cooling - IntroductionAre the people in this picture loosing heat

and gaining cold? How do you know?How do you think you could find out?

Main Idea – How does heat affect

matter?

Looking Ahead…Heating and cooling are important in the

everyday processThe particle theory related to heating and

coolingHeat is the transfer of energy from warmer

substances to cooler substancesMost materials expand when they are heated

and contract when they are cooledInvestigation skills can be used to learn about

expansion and contraction of different materials

VocabularyParticle theory of

matterHeatKinetic energy

TemperatureThermal energyThermal contractionThermal expansion

Heating Objects…What are some

example of things we heat everyday?

How does heating affect an object or material?

7.1 Warmth and Coldness What are some things that make us warm?

Make objects warm?How do we keep warm in the winter?

What are some things that make us cold? Make objects cold?

How do we stay cool in the summer?

Does a fridge only make things cold?

How do these animals deal with heat?Some fly south

during the winterSnakes and lizards

bake in the sun to keep their bodies warm

Honeybees flap their wings to cool their hives in hot weather

How do humans deal with heat?Dress in cool

clothingStay in air

conditioned placesLimit physical

activity in the heat

What happens when we get too hot?

Poor Insulation?Hot air leaks inHot air leaks out

Cold air leaks inCold air leaks out

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecAverage temp (°C) –10 –9 –2 6 14 18 21 20 15 6 1 –7

How can we stop air from leaking in and out?

7.2 Explaining Hot and ColdWhat are the parts to the particle theory?

How does the particle theory relate to a solid?

How does the particle theory relate to a gas?

How does the particle theory relate to a liquid?

HeatWhen an object is heated, the particles move

faster

When an object is cooled, the particles move slower

Read top of page 186

Will they survive?Volunteers – ball demo

Heat: is the transfer of energy from warmer things to cooler things

7.3 Kinetic Energy, Heat and TemperatureDEMO – solid, liquid or gas?Why?How do slow movements affect the shape?How do fast movements affect the shape?

Kinetic EnergyEnergy that all moving objects possess; a

particle has more kinetic energy when moving faster and less kinetic energy when moving slower

Particles of matter bump and collide at different speeds (bumper cars)

TemperatureA measure of the average kinetic energy of

the particles of a substanceThe average kinetic energy of hotter particles

is higherThe average kinetic energy of colder

particles is lower

The Particle Theory and the States of Matter

Solids

Liquids

Gases

SolidThe shapes and volumes of solids do not

change because the particles vibrate

The kinetic energy of particles is too low to overcome the forces holding the particles together

The particles are packed close together, and are difficult to fit into smaller spaces

LiquidTake the shape of their containers and have a

consistent volume

The particles move faster than that of a solid

There is still enough attraction between particles to keep them together but not tightly packed

GasExpand fully in an empty container – volume

and shape can change

The fast motions of the particles prevent their forces of attraction from holding them close together

Have very large spaces between them

Easy to compress

The Particle Theory and Changes of State

Thermal Energy: the total kinetic energy and energy of attraction of all the particles of a materialwe can increase the thermal energy of a

substance by heating it We can decrease the thermal energy of a

substance by cooling itChanges in thermal energy can cause a

substance to change states (solid to liquid, etc.)

Changes of state involve changes of thermal energy…

Condensation

Evaporation

Melting

Freezing

GASLIQUIDSOLID

SUBLIMINATION

DEPOSITION

Increasing thermal energy of particles

Decrease thermal energy of particles

Thermal ExpansionWhen solids, liquids or gases are heated,

their volumes increaseThe faster moving particles travel greater

distances, so the occupy more space

Thermal ContractionWhen solids, liquids or gases are cooled,

their volumes usually decreaseThe slower moving particles travel shorter

distances, so they occupy less spaceSlows down the particles so they have less

kinetic energy

Read page 189

7.5 Living with Thermal Expansion and ContractionWhat ‘things’ in our daily lives are exposed to

changing temperatures?What is the difference between thermal

expansion and thermal contraction? Thermal expansion – get bigger Thermal contraction – get smaller

Expansion and Contraction of Solids

What would happen to concrete if metal poles in the concrete expanded?

The concrete would crack and the structure would be damaged

How would you fix this? Put two solids together that can expand at the same

rate

Read page 192

Expansion and Contraction of GasesWhen gas is heated in a container, the

particles are pressing against the walls of the container until it eventually breaks

Example: filling a balloon with hot air until it eventually pops because it is too

full and because of the heatRead page 193

Expansion and Contraction of LiquidsGasoline that is left in the vehicle tank on a

warm day will expandTherefore you should always fill your gas

tank when it is colder outside because you can get more in