Transcript Heat transfer through the contact of two substances.

Heat and Temperature
Temperature
A measure of average kinetic energy of
the molecules in a substance.
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In open air water cannot reach temperatures
above boiling because the fastest moving
water molecules leave through evaporation.
Absolute zero occurs when there is no
energy in a substance.
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The molecules are stationary or there are no
molecules present.
Vacuum is the absence of matter.
Temperature Scales
Fahrenheit
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Freezing 32oF
Boiling 212oF
Fahrenheit to Celsius conversion
oC
= 5/9(oF ) + 32
Kelvin
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Absolute zero
Celsius to Kelvin conversion
K = oC + 273
Centigrade (Celsius)
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Freezing 0oC
Boiling 100oC
Celsius to Fahrenheit conversion
oF
= 9/5(oC - 32)
Feel The Heat
Heat is the transfer of energy between two
substances of different temperatures.
Energy travels from warmer to cooler
substances.
There are three forms of heat transfer
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Convection
Conduction
Radiation.
Energy Transfer
Convection: Heat transfer through fluids
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Includes gases.
Convective Cells
Hot air or fluids rise because they are less dense.
Colder denser air or fluid flows in from underneath to take
its place.
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Heat transfer through the atmosphere responsible for
weather patterns.
How thunderstorms are created.
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Responsible for currents in the ocean essential for
life.
Evaporative cooling occurs due to convection
Energy Transfer
Conduction: Heat transfer through the
contact of two substances.
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As molecules gain kinetic energy they
transfer that energy to other molecules and
set them in motion.
Conduction can lead to convection
Consider boiling a pot of water on a stove.
The molecules of a metal pot transfer their kinetic
energy to the water molecules.
Heat Transfer
Radiation: Transfer of heat through
electromagnetic waves.
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Unlike convection and conduction no
molecules are necessary for heat transfer.
Can travel through a vacuum.
This is infrared energy.
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Infrared images can locate tumors or see it
circulation is restored in damaged limbs.
Conductors
Conductors are substances that are that
can transfer heat.
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Metals are good conductors of heat.
Gases are poor conductors of heat because
the particles are too far apart.
Contact between molecules are necessary for heat
conduction.
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Liquids are better conductors of heat than
gases but do not conduct heat as well as
solids because they are not as compact.
Insulators
Insulators do no conduct heat well.
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Conductors are poor insulators.
Some good insulators are
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Air
Foam
Rubber
Wood
Insulation is used in houses to prevent heat loss.
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R value is a number that builders use to rate how effective an insulating
material is.
The higher the R value the better the insulation material.
Substance
R Value
Flat glass
0.89
Insulating Glass
1.54
Dry wall
0.45
Fiberglass
10.90
Specific Heat
Refers to the amount of energy necessary to
raise the temperature of a substance.
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The amount of energy in joules to raise 1 kg of
substance 1 degree Kelvin.
Substances with a high specific heat require a lot of
energy to change its temperature.
Water has a high specific heat
Rubbing alcohol has a low specific heat.
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Specific Heat Equation
Energy = specific heat x mass x temperature change
E
c
m
T
Air Conditioners
Remember, when a substances turns from a
liquid to a gas, energy is absorbed.
When gas condenses into a liquid energy is
released.
Air conditioners absorb energy from the air in
you house making the air in your house cooler
by using a liquid that evaporates easily.
The liquid condenses with temperature of the
air out side releasing energy.
Central Heating Systems
A furnace heats steam, water or air in pipes or
ducts that are circulated throughout the house.
Because the pipes are hotter than the
surrounding air heat leaves the pipe to warm the
surrounding air.
Solar panels collect heat from the suns energy
and it is stored and then transferred to pipes or
ducts much like a central heating system.