Grade 7 - Unit C
What are some things that keep us
warm?
What are some items that cool us
down?
Heating and Cooling - Introduction
 Are 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
process
 The particle theory related to heating and cooling
 Heat is the transfer of energy from warmer substances
to cooler substances
 Most materials expand when they are heated and
contract when they are cooled
 Investigation skills can be used to learn about
expansion and contraction of different materials
Vocabulary
 Particle theory of matter
 Temperature
 Heat
 Thermal energy
 Kinetic energy
 Thermal contraction
 Thermal 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 winter
 Snakes 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 clothing
 Stay in air conditioned
places
 Limit physical activity in
the heat
 What happens when we
get too hot?
Poor Insulation?
 Hot air leaks in
 Cold air leaks in
 Hot air leaks out
 Cold air leaks out
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Average 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 Cold
 What 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?
Heat
 When 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
Temperature
 DEMO – solid, liquid or gas?
 Why?
 How do slow movements affect the shape?
 How do fast movements affect the shape?
Kinetic Energy
 Energy 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)
Temperature
 A measure of the average kinetic energy of the
particles of a substance
 The average kinetic energy of hotter particles is higher
 The average kinetic energy of colder particles is lower
The Particle Theory and the States of
Matter
 Solids
 Liquids
 Gases
Solid
 The 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
Liquid
 Take 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
Gas
 Expand 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 material
 we can increase the thermal energy of a substance by
heating it
 We can decrease the thermal energy of a substance by
cooling it
 Changes in thermal energy can cause a substance to
change states (solid to liquid, etc.)
Changes of state involve changes of
thermal energy…
Increasing thermal energy of particles
SUBLIMINATION
Condensation
Freezing
Melting
Evaporation
SOLID
LIQUID
DEPOSITION
Decrease thermal energy of particles
GAS
Thermal Expansion
 When solids, liquids or gases are heated, their volumes
increase
 The faster moving particles travel greater distances, so
the occupy more space
Thermal Contraction
 When solids, liquids or gases are cooled, their volumes
usually decrease
 The slower moving particles travel shorter distances, so
they occupy less space
 Slows down the particles so they have less kinetic energy
 Read page 189
7.5 Living with Thermal Expansion
and Contraction
 What ‘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 Gases
 When 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 heat
 Read page 193
Expansion and Contraction of Liquids
 Gasoline that is left in the vehicle tank on a warm day
will expand
 Therefore you should always fill your gas tank when it
is colder outside because you can get more in