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1How Heat Moves

Review of past terms:

Define Energy:

The ability to do work or causechange.

What is the basic unit of measure

for energy?Joules.

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2How Heat Moves

Define Heat:

Heatis the movement of

thermal energy from asubstance at a highertemperature to another

substance at a lowertemperature.

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3The Nature of Heat

Heat moves in only one direction:

Under normal conditions and in nature,heat energy will ALWAYS flow thewarmer object to the cooler object.

Heat energy will flow from one substanceto another until the two substances havethe same temperature.

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4How Heat Moves

Thermal energy in the form ofheat can move in three ways.

ConductionConvection

Radiation

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5Conduction

CONDUCTION:

The transfer of heat from oneparticle of matter to another bydirect particle to particle contact.

Conduction occurs primarily in solidsbecause the particles are tightly packedtogether.

The particles themselves DO NOT changepositions.

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6Conduction

Example: A metal spoon in a pot ofwater being heated on an electric stove.

a. First, the electrical energy is converted

to thermal energy by the stove.b. The rapidly vibrating particles of the

hot electric coil collidewith the

particles of the cool pot.c. Heat energy is transferred, causing theparticles in the pot to vibrate faster.

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7Conduction

d. The rapidly vibrating particles of the pot nowcollidewith the particles of the water at thebottom of the pot.

e. The water particles absorb energyand vibrate

and flow more rapidly and its temperatureincreases.

f. Now, the energetic (hot) particles of watercollidewith the particles of the submergedend of the spoon.

g. As the particles of the spoon absorb energyand vibrate more rapidly. The temperature of

the spoon increases.

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8Conduction

h. As the particles at this end of the spoonabsorb energy and vibrate faster theycollide with other particles in the spoon.As they collide, energy is transferred tothe other particles (similar tomomentum) and they begin to vibratemore rapidly.

i. This process of conduction is repeatedall along the metal spoon until the entiremetal spoon becomes hot.

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9Conduction

Brainstorming: What are otherexamples of conduction?

Application: Describe the processof conduction when you place a hotspoon into a bowl of ice cream.

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10Convection

Convection: the transfer ofthermal energy (heat) throughthe bulk movement of matter.

Convection occurs in FLUIDS (liquidsand gases).

Convection produces CURRENTS in

both gases and liquids. Thermal Energy heat is carried by theparticles as they move from one location toanother.

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11Convection

Example: Heating water:

a. When the water at the bottom of thepot (nearest the burner) is heated, theparticles absorb energy by conductionas they touch the hot pot.

b. The water particles vibrate morerapidly.

c. The particles also move farther apartand the hot water becomes less densethan the surrounding cool water.

d. This causes the heated (hot) water torise.

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12Convection

e. The surrounding denser cooler water is

forced downward near the burner bythe rising hot water.

f. This process continues to repeat.

g. This FLOW creates a circular motionknown as a convection current .

Application: How do convectioncurrents form in a room when theheater is turned on?

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13Convection

The warm air from the heater vent will

rise. Why?, The warm air is less dense than the

surrounding cooler air.

The cool air is pushed down by the risingwarm air.

What is the best location for a heat vent in a room

and why? Near the ceiling or the floor?Floor:

Because the warm air will rise to the ceiling.

How about the return vent?

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14Convection

Convection currents occur in theenvironment as well. They produce:

Global winds that contribute to Earthsweather.

Ocean and lake currents

1

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15Convection

Brainstorming: On a hot summer daythe breeze near the beach blowstoward the water. However, later inthe day the breeze reversesdirection and blows toward land andwill get increasingly stronger. Why?

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16Convection

Answer: In the morning the watermay be warmer than the sandcausing the air over the water torise.

In the afternoon, the sand hasbecome much hotter than the water

and the air above it rises. The airover the water rushes in to fill itsvoid causing a wind.

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17Radiation

Radiation: the transfer of(thermal) energy by electromagneticwaves.

Radiation does not require matter to

transfer thermal energy. All the suns energy that reaches Earth

travels through millions of kilometers ofempty space (a vacuum).

All matter can radiate energy. You feel the radiation of thermal energy

from a bonfire, a heat lamp and a light

bulb.

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18Radiation

Other examples of the transfer ofheat by Radiation:

a. Charcoal grill.

b. Hot tin roof.c. Burner on a stove top.

d. ?e. ?

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19Radiation

Key Point: For radiation to be felt asheat it must first be absorbed by amaterial.

Example: Why do blue jeans feelhotter in the sun than a yellow shirt,even though they are both exposedto the same amount of sunlight?

The blue jean fabric absorbs moreradiant energy from the sun than the

yellow shirt because of its dark color.

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20Conduction, Convection & Radiation

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21Energy from the Sun

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22Convection, Conduction & Radiation

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23

The Nature of Heat

What happens when you put ice in awarm soft drink?

The heat energy moves from the softdrink into the ice by conduction(particle to particle contact) causingthe ice to melt.

24R

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24Review

Describe the three kinds of heat

transfer.a. Conduction transfer of heat energy from

one particle to another by direct contact.

(Primarily in solids)b. Convection transfer of heat energy influids-gases and liquids) through the bulkmovement of matter from one place toanother. (Produces currents)

c. Radiation transfer of energy throughelectromagnetic waves. (Matter is notrequired!) (Radiant & infrared radiationfrom the sun)

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25Conduction

Directcontact ofparticles

Solids/liquids/gases

The handleof a cookingutensil

Transfer ofenergy bywaves

Only radiantenergy thatis absorbedbecomesthermalenergy

Lightbulb Fireplace

Transfer ofenergy bybulkmovement ofmatter(fluids)

Currents(wind,water)

Hot airballoon

Radiation Convection

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Direct contact of particlesSolids/liquids/gases

Solids -good conductorsGases -poor conductors

Transfer of energy bybulk movement ofmatter (fluids)Currents (wind,water)Hot air balloon

Transfer of energyby wavesOnly radiant energythat is absorbedbecomes thermal

energyShiny/light colors-reflectDull/dark colors-absorb

Radiation

Conduction

Convection

Contrast:Conduction

ConvectionRadiation