Heat is another word for thermal thermal energyenergy.

Heat Transfer

Heat energy always moves from warmwarm to coldcold, until the system

reaches equilibriumequilibrium (balance).

Heat can be transferred (moved)transferred (moved) 3 ways:

radiationradiation: electromagnetic (EM) waves that travel through space, and transfer their energy as heat when they reach an object.

conductionconduction: direct contact between molecules. convectionconvection: up-and-down movement of fluids (liquids and gases) due to differences in temperature and density (hot fluids rise , cold fluids sink ).

Heat Transfer

CONDUCTIONCONDUCTION the metal spoon in your hot chocolate gets hot after a while a cold can of soda gets warm after it’s been out of the refrigerator for a while

Everyday Examples:

CONVECTIONCONVECTION the attic of your house is always warmer than the basement. drafts of cold air come in at the bottom of the door, not the top.

RADIATIONRADIATION solar panels collecting and storing solar energy dark clothes are hotter on a sunny day than white clothes.

If a material allows heat to pass through it quickly, it is called a good conductor.

(Examples: metal, glass)

Conductors & Insulators

If a material does not allow heat to pass through it quickly, it is called a good insulator.

(Examples: plastic, wood)QuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

• Fast-moving, high-energy molecules collide with the slow-moving, low-energy molecules, transferring their energy (heat) to them.

Heat Transfer Heat Transfer by Conductionby Conduction

http://www.echalk.co.uk/Science/physics/convection/convection.html

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=SCE304

Heat Transfer by ConvectionHeat Transfer by Convection• When molecules absorb heat, they move faster, spread out and rise because they are less less densedense.• When molecules lose heat, they slow down, come closer together and sink because they are now more densemore dense.

This is why we say “Heat rises, cold sinks.” It’s actually more accurate to say “High-energy molecules rise, low-energy molecules sink,” but that takes way too long to say.

• Radiation moves energy without any help from particles of matter.• The Sun’s energy radiatesradiates ((travels in wavestravels in waves)) through space to reach Earth. • Energy that travels by radiation is called electromagnetic (EM) waveselectromagnetic (EM) waves. Light is one kind of EM radiation we can see, but visible light is just one tiny part of the EM spectrumEM spectrum.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Heat Transfer by RadiationHeat Transfer by Radiation

RadiationRadiation

http://www.spaceflight.esa.int/impress/text/education/Heat%20Transfer/Radiation.html

As the wave’s wavelengthwavelength decreases decreases (shortens), the amount of energy amount of energy it carries increasesincreases.

micrometer

Electromagnetic (EM)spectrum

Photo of infra-red radiation (heat) coming

from a catAlthough we can’t see it, the heatheat we feel on our skin when we stand in the sun or put our hands over a hot stove is caused by infrared infrared radiationradiation, another type of EM EM radiationradiation. .

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=SCE304

The 3 Kinds of Heat Transfer

All 3 kinds

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Fire transfers heat energy 3 ways:

http://www.spaceflight.esa.int/impress/text/education/Heat%20Transfer/Convection%20in%20a%20Liquid.html

Convection

Convection currents: currents in fluids (liquids or gases) that transfer heat as warm fluids rise and cold fluids sink.

Convection Convection Currents in Currents in the Earth’s the Earth’s atmosphereatmosphere

ConvectioConvection n

Currents Currents in the in the

Earth’s Earth’s mantlemantle

Convection currents in the atmosphere & mantle

Convection currents in the earth

Most of our weather weather is the result of convection currentsconvection currents in the atmosphereatmosphere.

convection

– fuel is burned in a furnace and a fan circulates the heat in the house

Which method of heat transfer is being used here?

Forced-Air Heating Systems

Which of the following best explains why the end of a spoon sticking out of a cup of hot water also gets hot?

The hot water causes a chemical reaction to occur in the spoon.

The heat from the hot water is conducted through the spoon to the handle.

The hot water heats the air surrounding the upper part of the spoon.

The hot water causes a physical change in the spoon handle.

When it is very hot in his room, Stuart makes it cooler by opening both the top and the bottom of his window. Which statement best explains why this works?

Air comes in the top to cool the ceiling and in the bottom to cool the floor. Cooler air comes in the bottom and warm air goes out through the top. Warmer air goes out through both the bottom & top. It does not make any difference because if there is no wind, the air will not come in.

In which situation has heat energy moved mainly by conduction?

A radiator heated with hot water warms a room.

The person sitting closest to the blazing fire finds it necessary to move farther from the heat.

The handle of a cast iron skillet being used to cook something becomes too hot to touch.

The red-hot coil of an electric space heater is used to keep a small room warm.

Which BEST explains how the food on the stove is being heated? conduction convection interaction radiation

A hot wood stove heats an entire room. The handle of a pot that is being heated becomes warm. A teaspoon in a glass of hot tea becomes warm. The coils of a toaster become red.

Which of the following is an example of heat transfer by convection?

What is the process by which heat energy gets to Earth from

the Sun?

conduction conduction radiation radiation subduction subduction convection convection

What is the process by which heat energy gets to Earth from

the Sun?

conduction conduction radiation radiation subduction subduction convection convection

Patti used a steel wrench to work on her bicycle on a hot, sunny day. She left the wrench on the hot concrete for an hour, then returned, to find the wrench very hot to touch. What is the BEST explanation for how the wrench got so hot?

Heat transferred from the wrench to the air.

Heat transferred from the bicycle to the wrench.

Heat transferred from the wrench to the concrete.

Heat transferred from the concrete to the wrench.