thermal energy transfer review 2012 13

7/27/2019 Thermal Energy Transfer Review 2012 13

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The Movement of HeatHeat is thermal energy moving from a

warmer object to a cooler object. This

is known as thermal transfer.


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Heat Transfer Facts:

Heat always moves from a warmer

place to a cooler place

o Hot objects in a cooler room will cool toroom temperature

o Cold objects in a warmer room will heat

up to room temperature


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Question

If a cup of coffee and a popsicle were left

on the table in this room what would

happen to them? Why?

Answer: The cup of coffee will cool

until it reaches room temperature.The popsicle will melt and then the

liquid will warm to room temperature.


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How is Heat Transferred?

Heat transfers in THREE ways:

Conduction

Convection

Radiation


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CONDUCTION

Heat is transferred from one particle of

matter to another in an object without the

movement of the object.

Conduction = CONTACT


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Have you ever

Touched a metal spoon sitting in a pan of boilingwater only to be surprised by hot HOW it is??

Think back to what you know about metals and

nonmetals. What conducts heat better? Metal

or Nonmetal? Why?


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Example of

Conduction

Think of a metal spoon in a pot

of water being heated.

The fast-moving particles of the

fire collide with the slow-movingparticles of the cool pot.

Because of these collisions, the

slower particles move faster

and heat is transferred.

Then the particles of the potcollide with the particles in the

water, which collide with the

particles at one end of the

spoon.

As the particles move faster, the

metal spoon gets hotter. This

process of conduction is

repeated all along the metal

until the entire spoon is hot.


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Examples of Conduction

A piece of metal in a forge glows red as

heat is transferred to the metal from the

forge.


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Conduction

When you heat a metal strip at one end, the heat

travels to the other end.

As you heat the metal, the particles vibrate, these

vibrations make the adjacent particles vibrate, and so on

and so on, the vibrations are passed along the metal and

so is the heat. We call this? Conduction


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Metals are different

The outer e______ of metal atomsdrift, and are free to move.

When the metal isheated, this sea ofelectrons gain k_____energy and transfer itthroughout the metal.

Insulators, such as w___ and p____, do nothave this sea of electrons which is why theydo not conduct heat as well as metals.

lectrons

inetic

ood lastic


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Why does metal feel colder than wood, if they

are both at the same temperature?

Metal is a conductor, wood is an insulator. Metalconducts the heat away from your hands. Wood

does not conduct the heat away from your hands as

well as the metal, so the wood feels warmer than

the metal.


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CONVECTION

Convection is the movement that transfers heatwithin fluids (air and gas)

Heat is transferred by currents within the fluid or

gas

Convection = VENTS through air and liquid

particles

Convection moves in a circular pattern


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Examples of Convection: Have you ever noticed that the air near the

ceiling is warmer than the air near the floor? Orthat water in a pool is cooler at the deep end?

Examples: air movement in a home, pot of

heating water.

Pick one of these examples and draw the

circular pattern in your notes.


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Explaining Convection

Convection currents

cause the coolerbreezes you

experience by a

large body of water

These currents also

cause the

movement ofmagma within the

earth.


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Convection

What happens to the particles in a liquid or a

gas when you heat them?

The particles spread out andbecome less dense.

This effects fluid movement.What is a fluid?A liquid or gas.


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Water movement

Hot water

risesCooler

water sinks

Convection

current

Cools at the

surface


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Why is it windy at the seaside?

C ld i i k


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Cold air sinks

Where is thefreezercompartment

put in a fridge?

Freezercompartment

It is put at thetop, becausecool air sinks,

so it cools thefood on theway down.

It is warmerat the

bottom, sothis warmerair rises and

a convectioncurrent is

set up.


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RADIATION

Radiation is the transfer of energy by

electromagnetic waves

Radiation does NOT require matter to transfer

thermal energy

Radiation = RADIATES (heat escaping the sun)

Th thi d th d f h t t f


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The third method of heat transfer

How does heat energy get

from the Sun to the Earth?There are no particlesbetween the Sun and the

Earth so it CANNOT

travel by conduction or

by convection.

?RADIATION


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Radiation Comes From Other Sources

Have you ever sat too close to a campfirewhile cooking marshmallows (enjoying the

warmth) only to notice that your skin is really

warm?


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Examples of Radiation

1. Fire2. Heat Lamps

3. Sun

R di ti


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Radiation

Radiation travels in straight lines

True/False

Radiation can travel through a vacuum

True/False

Radiation requires particles to travel

True/False

Radiation travels at the speed of light

True/False

C ti ti


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Convection questions

Why are boilers placed beneath hot watertanks in peoples homes?

Hot water rises.

So when the boiler heats the water, and the hot waterrises, the water tank is filled with hot water.

Why does hot air rise and cold air sink?

Cool air is more dense than warm air, so the

cool air falls through the warm air.

R di ti ti


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Radiation questions

Why are houses painted white in hot countries?

White reflects heat radiation and keeps the house cooler.

Why are shiny foil blankets wrapped around marathon

runners at the end of a race?

The shiny metal reflects the heat radiation from the runner

back in, this stops the runner getting cold.


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Thermal Heat Transfer Quiz

How much do you know about thermal

heat transfer???

Show what you know!!


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1. Which of the following is not a

method of heat transfer?A. Radiation

B. InsulationC. Conduction

D. Convection


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3. How does heat energy reach

the Earth from the Sun?A. Radiation

B. ConductionC. Convection

D. Insulation


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Thermal Energy Transfer

thermal energy transfer review 2012 13

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