Energy Transfer as Heat

S8P2 d.Describe how heat can be

transferred through matter by collisions of atoms

(conduction) or through space (radiation). In a

liquid or gas, currents will facilitate the transfer of

heat (convection).

Background• All forms of matter, whether solid, liquid, or gas,

are composed of atoms or molecules in constant motion

• Because of this constant motion, all atoms have thermal (heat) energy

• Whenever a substance is heated, the atoms move faster and faster

• When a substance is cooled, the atoms move slower and slower

• The “average motion” of the atoms that we sense is what we call temperature

• Temperature and heat ARE NOT technically the same thing

• Temperature is the average motion of atoms and molecules; heat is the energy that flows due to temperature differences

Lesson Essential Question:

How is energy transferred as

heat?

How is energy transferred as heat?

Activating Strategy:

Activating AcrosticFor each of the letters of the phrase on the following slide

write one word that would characterize the phrase.

H -E -A -T -

T -R -A -N -S -F -E -R -

The transfer of energy between the

particles of two objects due to a

temperature difference between the two objects is

called heat.

• The transfer of energy always takes place from a substance at a higher temperature to a substance at a lower temperature

• Temperature is an indicator of the particles’ average kinetic energy; therefore, you can use it to predict which way energy will be transferred

• The greater the difference in the temperatures of two objects, the more energy that will transfer as heat

Energy can be transferred as heat in

three ways:•Conduction

•Convection

•Radiation

Conduction

Conduction

Conduction is the transfer of energy that occurs when molecules bump into one another (heat transfer from one

atom to another within a substance).

ConductionMolecules are always in motion, but molecules in

warmer objects move faster than molecules in cooler

objects.

Solid at Different Temperatures

ConductionWhen objects are in contact, energy is transferred from warmer objects

to cooler objects.

ConductionExample of conduction: A spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the

spoon

Conduction is most effective in solids, but it can happen in fluids. Gases and liquids are generally poor conductors of heat because their molecules

are farther apart than are the molecules in solids. Therefore, neighboring molecules in a

gas or in a liquid are less affected by the increased motions of heated molecules, and consequently heat is not conducted rapidly.

Conduction

Use the following website to view animations of energy transfer by conduction in solids, liquids, and

gases.

http://www.scienceonline.co.uk/energy/conduction2.html

Conduction

Why does the lady in the pink dress drop her roasting stick when the lady in the blue dress does not?

When heat is conducted, it is led from the heat source by traveling along a

physical object. The young woman in the pink dress was using a

straightened out coat hanger wire to cook her marshmallow. Metal is a

good conductor of heat. The heat from the fire traveled along the thick metal wire. The wire got so hot that the girl had to let go of it. The young girl in the blue dress is using a wooden rod to hold her marshmallow. Wood does not conduct heat well. The wood in

her hand is still cool and the marshmallows are almost done!

Conduction• Any material through which energy can be

easily transferred as heat is called a conductor• What determines how well a substance

conducts is whether it is a gas, liquid, or solid• Gases are extremely poor conductors because

their particles are far apart• Liquids conduct better than gases, but they

are still not very effective conductors• Some solids, like rubber and wood, conduct

energy about as well as liquids• Metals such as copper and silver conduct heat

transfer very well• Some solids conduct better than others• In general, metals are better conductors than

nonmetals

Conduction

A material that is a poor

conductor that is used to reduce or stop energy is called an insulator

Ex. Wood

Conductivity Chart

Convection

Convection

Convection is the transfer of heat by the

flow of material. Convection circulates

heat.

Convection• Heat moves with the fluid• Warmer portions are less dense

and therefore rise; cooler portions fall because they are denser. When the atoms at the top cool down, they become more dense and fall and vice versa for the warmer atoms. Hence a continuous cycle

• The cycle of a heated fluid that rises and then cools and falls is called a convection current

Convection

Convection occurs mostly in gas or liquid.

Convection

Convection

Use the following link to observe an animation of

convection:

http://www.geophysik.uni-frankfurt.de/~schmelin/what-is-convection.html

Scroll down to the 3rd animation at the bottom of the page

Radiation

RadiationRadiation is energy that

is transferred in the form of rays or

electromagnetic waves. This includes infrared radiation, visible light, and ultraviolet rays.

RadiationWhat happens in space?

•There are no solids touching the sun for conduction to occur

•There are no fluids in space for convection to occur

•Therefore, heat travels by radiation

Use the animations on the website below to review

conduction, convection, and radiation:

http://www.bbc.co.uk/science/hottopics/cooking/chemistry.shtml

Scroll down until you see the stove

Think, Pair, Ink

Look at the diagram below. In a sentence or two

explain how radiation, conduction, and convection

are used or prevented.

The shiny inside reflects radiant energy back into

the fluid. It also prevents heat from entering the

thermos from outside. The vacuum space prevents

conduction and convection from occurring. Since heat

cannot easily leave or enter the thermos, fluids

retain their original temperature.

Conduction, Convection, and

Radiation together distribute the Sun’s heat throughout the

Earth

Lesson Essential Question:

How is energy transferred as heat?

Summarizing Strategy:

On the following slides, identify whether the

statement describes cooking popcorn using conduction, convection, or radiation.

Put oil in the bottom of a pan. Cover the bottom of

the pan with popcorn kernels. Place the pan on the stove and turn on the burner to medium heat. Cover the pan with a lid.

Periodically shake the pan so the kernels move around

in the oil.

And the answer is…

Conduction

The heat is transferred by direct contact from the pan, to the oil, to the kernels of

popcorn.

Microwave a bag of popcorn.

And the answer is…

Radiation

The kernels are heated by the radiation in the

microwave.

Cooking popcorn in a popcorn popper.

And the answer is…

Convection

The hot air transfers the heat to the cooler kernels, and when

enough hot air heats the kernels they pop.