# 10721928

```Grade 7 Science
Unit 2
Heat is transferred from one place to
another by three different processes.
Chapter 6
Heat Transfer
 Heat transfers from a hot object to a
cold object.
 Heat moves NOT cold
 Something cold is really just
something less hot
3 Types of Heat Transfer
1.Conduction
2.Convection
1. Conduction
 Particle movement:
 the particles in an object vibrate in place
but collide with neighbouring particles
passing kinetic energy to them.
 State(s) in which it occurs:
 Can happen in Solid, liquid and gas
 Best in solid’s worse in gases
 The particles stay in position!
Examples of conduction
 Cooling on a stove
 Ice packs
 Can you think of other examples?
Conduction mini experiment
 Comparing conduction
 Do some materials conduct better
than others?
2. Convection
 Particle movement:
 When heated the particles gain energy,
spread out, become less dense and rise.
As it cools, the particles lose energy, get
closer together, become more dense and
sink.
 State(s) in which it occurs:
 Can happen in liquids and gas
 Not in Solids!
Examples of Convection
 Boiling water on the stove
 Can you think of
other examples?
Convection Demonstration
 convection currents using a
convection box or convection tube
 Particle movement:
 No particles!!
 electromagnetic waves carry energy
from a source to another object.
 State(s) in which it occurs:
 Any or none! No state necessary
 Can occur in the vacuum of space
 Fireplace
 Sunlight
 All 3 can happen at the same time!
1. Reflect: bounce of shiny, smooth
surfaces
2. Absorb: Taken in by rough, dull
coloured surfaces (gets warmer)
3. Transmit: Moves through glass,
plastic, paper.
 Interactive:
 http://www.pbslearningmedia.org/ass
et/lsps07_int_heattransfer/
 Online Practice:
 http://www.webquest.hawaii.edu/kah
ihi/puzzles/energytransfer/index.php
Core Lab Activity!
Activity 6-1D
“Absorb That Energy”
Page 184
Home Heating!
 Brainstorm: How do we heat our homes?
The Past
The Present
Home Heating Technology
 Wood stove
 Electric Heaters
 Oil Furnace
 Air to Air Heat Pump
 Geothermal
 Solar
Oil furnace
Air to air
Geothermal
Core STSE
“Heat Pumps: An Alternative Way
to Heat Homes”
Section Review Questions
 Page 191 Q’s: 1, 2, 3, 4 & 9
Conductors Vs. Insulators
Thermal
Conductor
Allows Heat to
Transfer
Thermal
Insulator
Prevents Heat
from Transferring
Ex. Metal (some
metal are better
than others)
Ex. Wood, plastic
Thermal conductors
 Allows heat to travel
 Cookware – warms your food
Thermal insulators
 Keeps Items Warm!




Animal Fur – animals/humans
Sod – houses in the past
Fibreglass – houses in the present
Thermos - food
How does a thermos work?
 A vacuum exists
between the layer
 No particles means
little heat transfers!
Try it out!
 Interactive mini-lab
 http://www.bbc.co.uk/schools/scienc
eclips/ages/8_9/keeping_warm.shtml
Section Review Questions
 Page 205 Q’s: 1, 2& 9
Heat Vs. Temperature
 Heat: The energy which is transferred from
hotter substances to colder ones.
 Note: cold doesn’t move, heat does!
 Heat: the total
energy
 Temperature: the
average energy
Specific Heat Capacity
 Specific Heat Capacity: Measures
the amount of heat transferred
 The amount of heat needed to raise
the temperature of 1.00 g of a
substance by 1.00˚C.
Specific Heat Capacity
 High specific heat capacity takes a lot
of heat to warm up
 A lot of heat transfers
 Low specific heat capacity takes only
a little heat to warm up
 Only a little heat transfers
Specific heat capacities of various
substances
 Don’t Need to memorize these!
Which has a higher Specific Heat
capacity?
 Water or soil?
 On a hot day which warms up more
quickly – the water or sand?
Which has a higher Specific Heat
capacity?
 Water or soil?
 Soil!
 On a hot day which warms up more
quickly – the water or sand?
 Sand! It cools more quickly as well
Question 1
 Why do metal objects often feel
colder than the surrounding air
temperature?
Question 1
 Why do metal objects often feel
colder than the surrounding air
temperature?
Not because the metal is colder
 Metal has a low specific heat capacity, it will
quickly absorb heat!
 The heat from our hands is transferred to the
metal quickly
 This makes our fingers cold – the metal feels
cold!
Question 2
 Why does a piece of aluminum
foil feel cool after taken out of
the oven for only minutes?
Question 2
 Why does a piece of aluminum foil
feel cool after taken out of the
oven for only minutes?
 The aluminum has a low specific heat capacity.
 It quickly takes in heat, but also loses it quickly
 It doesn’t take much heat to warm it up so it
will lose that small amount of heat quickly
Question 3
 Why should you be cautious when
eating an apple pie which has been
taken from the oven for twenty
minutes?
Question 3
 Why should you be cautious when
eating an apple pie which has been
taken from the oven for twenty
minutes?
 The apple pie has a high specific heat capacity.
 It takes a lot of heat to warm it up so it will
take a long time to lose all of that heat!
Interactive
 comparing specific heat interactive:
 http://oceanservice.noaa.gov/educati
on/pd/oceans_weather_climate/medi
a/specific_heat.swf
Discussion: Sea and Land Breeze
Heat and Technology
 The need to stay warm have led to
many new technologies (past and
present)
 Make a list of heat-technologies with
a partner (come up with as many as
possible!)
Section Review Questions
 Page 215 Q’s: 1, 2, 3 & 7
Chapter Review Questions:
 Page 216-17 Q’s: 1, 3, 5, 7, & 16
Unit Review Questions:
 Page 216-17 Q’s: 3, 4, 12, 13, 18,
19, 26, 31, 35 & 40
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