HEATHEATHEATHEAT________________Heat is the transfer of thermal energy between objects. Heat always flows from warmer objects to cooler objects.

WarmThermalEnergy Cool

Water Temperature

25 oC

How Ice Cools Water

ThermalEnergy

Water Temperature

21 oC

Water Temperature

18 oC

Water Temperature

15 oC

Water Temperature

12 oC

Water Temperature

10 oC

TemperatureTemperature is the measure of

how fast molecules of a substance

are moving. The faster the

molecules move, the higher the

temperature. Even in solid objects,

the molecules are moving, it’s just

that they are vibrating in place.

Thermometer 100

90

80

70

60

50

40

30

20

10

0

-10

Thermometer 100

90

80

70

60

50

40

30

20

10

0

-10

Temperature Scales

212 100

32 0

The two temperature scales that are most commonly used are:

• Fahrenheit

• Celsius (Centigrade)

Another scale, the Kelvin scale, is also used commonly in the scientific community.

Water

Freezes

Water

Boils

Fah

renh

eit

Cel

sius

Temperature ScalesTemperature Scales

• Degrees CelciusDegrees Celcius, 00CC, on the Celcius scale on the Celcius scale water freezes at 0 water freezes at 0 00C and boils at 100 C and boils at 100 00CC

• Degrees FarenheitDegrees Farenheit, , 00F on the Farenheit F on the Farenheit scale water freezes at 32 scale water freezes at 32 00F and boils at F and boils at 212 212 00FF

• Degrees KelvinDegrees Kelvin, , 00K starts at absolute zero K starts at absolute zero 0 0 00K, water freezes at 273 K, water freezes at 273 00K and boils at K and boils at 373 373 00K K

What is What is Absolute ZeroAbsolute Zero??

• Absolute zero, 0 Absolute zero, 0 00K,K, is the point where is the point where there is no molecular movement and there is no molecular movement and therefore no thermal energy, therefore no thermal energy, no heatno heat..

• Absolute zero Absolute zero is a theoretical number.is a theoretical number.

• Since the molecules of all matter are Since the molecules of all matter are moving, moving, all matter has heatall matter has heat..

Conductors are materials that

allow heat to transfer easily.

Conductors are usually made

from materials that have atoms or

molecules that are relatively close

together. This allows the heat to

“jump” from one molecule to the

next. Materials such as metals are

good conductors.

HEATHEAT

Insulators are materials that

do not allow heat to transfer

easily. Insulators are usually

made from materials that

have atoms or molecules that

are relatively far apart.

Materials such as plastic,

rubber, wood, gases (air) are

good insulators.

GLASS

GLASS

Heat

Gas

GLASS

GLASS

Heat

Gas

Heat TransferAs mentioned before, thermal energy

always goes from the warmer object to the

cooler object. This can happen in three

ways:

A) Conduction

B) Convection

C) Radiation

ConductionConduction is the transfer of thermal energy

through the direct contact of particles. One

particles gains thermal energy and then

transfers it to the particles closest to it. The

closer the particles are to each other, the

better the transfer of thermal energy.

HEATHEAT

ConvectionConvection is the transfer of thermal energy through

the movement of fluids. As a fluid gets warmer, its

density gets lower. As a result, the warmer fluid is

pushed up and rises (hot air balloons work because of

this principle). As it rises, it carries it thermal energy

along with it, passing it to other particles as it travels.

When it loses thermal energy, the density increases,

causing it to sink and repeat the cycle once again.

`

Convection Under the Earth’s Surface

RadiationRadiation is the transfer of thermal energy

through the electromagnetic waves. Unlike

conduction and convection, radiation does not

need something (a medium) to transfer heat.

The Sun, 93,000,000 miles from Earth, has no

direct contact with Earth and nothing known

flows between the Earth and the Sun. The only

way the Earth can receive it’s energy from the

Sun is radiation.

RadiationConvection

Conduction

Heat Transferin the

Atmosphere

Thermal Expansion

As an object gets warmer, its molecules move

farther apart and the object expands. Also, the

when an object cools, its molecules get closer

together, and the object shrinks or contracts.

IMPORTANT: Water is an exception to the

contraction rule. As water cools, it contracts until

it reaches 4 oC. Below 4 oC, water expands!

The shape of water

molecules and their

arrangement when they

become solid causes

water to expand as it

freezes.

Solid

Liquid

Gas

Tracks

put down

straight

in

February!

As seen

in

August!