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Grade 7 Science. Unit 2: Heat Chapter 6: “Heat is transferred from one place to another by three different processes.”. Heat Transfer. Heat transfers from a hot object to a cold object. Three types of Heat Transfer. Conduction Convection Radiation. 3 Types of Heat Transfer.

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Grade 7 Science

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Grade 7 science l.jpg

Grade 7 Science

Unit 2: Heat

Chapter 6: “Heat is transferred from one place to another by three different processes.”


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Heat Transfer

Heat transfers from a hot object to a cold object.


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Three types of Heat Transfer...

  • Conduction

  • Convection

  • Radiation


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3 Types of Heat Transfer


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1. Conduction

  • Occurs when the particles in an object vibrate in place but collide with neighbouring particles passing kinetic energy to them.


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  • The particles do not leave their original position.

  • Conduction occurs in most solids.


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Stainless Steel Sides

Copper Bottom


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Ice Packs


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2. Convection

  • Occurs when warm fluids move from one place to another.

  • Occurs in liquids and gases.


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When air warms, 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.

Convection Currents


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3. Radiation

  • Occurs when electromagnetic waves carry energy from a source to another object. The object absorbs the energy of the electromagnetic wave.


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  • There are no particles involved.

  • The waves can travel in a vacuum.


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Types of Electromagnetic Waves


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Radiant energy can be...

1. Reflected

Shiny, smooth,

light-colored

surfaces.


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2. Absorbed

Dull, rough,

dark-colored

surfaces.

Object will become

warmer.


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3. Transmission

The radiant

energy passes through.

Ex. Plastic, glass, paper,

etc.


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Absorption

Reflection

The Microwave

Transmission


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The three types of heat transfer, conduction, convection and radiation, can occur at the same time. For Example...


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Activity 6-1 CPage 182

Energy Transfers and Home Heating Systems


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Core Lab Activity

Activity 6-1D

“Absorb That Energy”

Page 184


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Home heating technologies...

1. Open Fireplace

  • Radiant heat from the fire and convection currents in the air spread the heat.


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2. Wood Stove

  • Efficient radiators due to the black color.


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2. Electric Heaters


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3. Oil Furnace

  • Air is drawn into the furnace and heated and fans would blow the warm air through the ducts into the rooms.

  • Water carried in a system of pipes can be used instead of air. (Hot water radiation)


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Forced-air furnace


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Hot Water Radiation


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4. Air to Air Heat Pump

  • Can be used to cool the home in the summer and heat the home in the winter.

Heat is exchanged with the outside air.


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5. Geothermal

  • Heat is exchanged with the ground.

  • In the summer, heat is pumped into the ground and in winter it is pumped up from the ground.


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Geothermal


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6. Solar

  • Converts light energy to electrical energy.


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Solar Panels


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Core stse

“Heat Pumps: An Alternative Way to Heat Homes”


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Conductors vs. Insulators

Conductors

  • Allow heat transfer

  • Ex. Metal (some metal are better than others)

Insulators

  • “Prevents” heat transfer

  • Ex. Wood, plastic


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Uses of Conductors

Cookware

Car Radiator


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Use of insulators

Animal Fur

Sod


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Fibreglass

Thermos


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The vacuum layer has no particles which prevents heat transfer.

Note: It is impossible to create a perfect vacuum.

Thermos


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Heat vs. Temperature

Heat is the energy which is transferred from hotter substances to colder substances.

It is the sum total of the energies of the particles in a substance. (Thermal energy)


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1+2+3+3+2+4+2+5+2+2

= 26J

26 ÷10 = 2.6 ˚C

Heat

Temperature

3

2

2

4

2

3

1

2

5

2


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Specific heat capacity

The amount of heat needed to raise the temperature of 1.00 g of the substance by 1.00˚C.

Used to measure the amount of heat transfer.


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Different materials have different capacities for storing heat. This depends on:

  • Molecular structure

  • Phase

  • Molecular mass

  • Shape

  • Surface area


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Specific Heat Capacities


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Specific Heat Capacity An Example...


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Temperature Heat & technology

With a partner, list as many technologies that deal with the idea of temperature and heat.


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