HEAT HEAT ____ ____ Heat is the transfer of thermal energy between objects. Heat always flows from warmer objects to cooler objects. Warm Thermal Energy Cool
Dec 28, 2015
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.
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.
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.
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.
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.
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