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 3.Radiation

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  Radiators  Can you think of other examples?

Convection Demonstration  convection currents using a convection box or convection tube

3. Radiation  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

Examples of Radiation  Fireplace  Sunlight

 All 3 can happen at the same time!

3 ways radiant energy transfers 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:  et/lsps07_int_heattransfer/ et/lsps07_int_heattransfer/  Online Practice:  ihi/puzzles/energytransfer/index.php 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 PastThe Present

Home Heating Technology  Wood stove  Electric Heaters  Oil Furnace  Air to Air Heat Pump  Geothermal  Solar

Oil furnace

Hot-water radiation

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 Thermal Insulator Allows Heat to Transfer 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 Car Radiator – warms your car

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  eclips/ages/8_9/keeping_warm.shtml 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?  Think about it:  On a hot day which warms up more quickly – the water or sand?

Which has a higher Specific Heat capacity?  Water or soil? Soil!  Think about it:  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:  on/pd/oceans_weather_climate/medi a/specific_heat.swf 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 Q’s: 1, 3, 5, 7, & 16

Unit Review Questions:  Page Q’s: 3, 4, 12, 13, 18, 19, 26, 31, 35 & 40