Heat
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Transcript of Heat
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HeatChapter 9 Thermal Energy
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Kinetic and Potential Energy• Kinetic energy- energy of motion
• potential energy – Is the certain amount of energy that Molecules have that is ABLE to be changed to kinetic energy
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*Thermal Energy• Both the potential energy + the kinetic energy
of all the molecules in an object is: Thermal Energy.
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What is Temperature?• Temperature- is a measure of the average
movement of molecules(kinetic energy)
• (You know it as “How hot or cold something is”)
–Higher temperatures mean faster moving molecules in a substance
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Temperature Scales• Three Common Temperature Scales (units)– Fahrenheit is used mainly in the United States
– Celsius is based on water’s freezing and boiling points
– Kelvin, uses zero as absolute zero, the lowest temperature an object can have.
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Converting Temperatures
• Convert Fahrenheit to CelsiusC = 5/9 ( Temperature in Fahrenheit - 32)
• Convert Celsius to Fahrenheit F = 9/5 ( Temperature in Celsius) + 32
• Convert Celsius to KelvinK= Temperature in Celsius + 273
PEMDAS DOES COUNT!!!!!
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Thermal Expansion• When most substances are heated they expand,
The amount they expand depends on the material and temperature
– That means the molecules speed up and tend to move farther apart
*This means things that are cooled slow down their particles, which get closer….causing it to contract or shrink
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Heat Transfer Chapter 9
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What is Heat?• Heat- A form of energy (thermal) made by the
motion of molecules. – The more movement of molecules the more heat
energy– Heat energy has the ability to do work
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Finishing Heat’s Definition• Heat: is thermal energy that is TRANSFERRED
from one object to another when the objects are at different temperatures.
• So there must be a difference in temperatures for heat to transfer!
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DO NOT WRITEHeat & States of Matter
• Solids have vibrating particles, not moving freely,– add heat and the solids melt, to liquids
• Liquids have less restricted moving particles– Add heat and the liquid evaporates
» To the most freely moving particles of a gas
• The opposite is true when you remove heat, from gas to liquid to solid
*Thermometers
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Transferring Heat• Heat ONLY flows from warmer objects to
cooler objects– Heat NEVER flows from colder objects to
warmer objects– Heat transfer occurs in three ways• Conduction• Radiation• Convection
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Conduction• Conduction- This is the transfer of heat by
direct contact…– …This is done by the contact between particles of
high kinetic (moving) energy to particles of low kinetic energy
– Transfer will continue until all particles have the same kinetic energy and are the same temperature
– Occurs more easily in solids and liquidsExample:
Attempting to eat a hot pocket and you burn your mouth
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Radiation • Radiation- Transfer of energy by electromagnetic waves.• This can occur in space
or through matter since it does not require particles to transfer the energy
• This is how the sun’s energy reaches Earth
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Convection• Convection- Heat transfer that occurs in moving
fluids (liquids and gases), the movement of molecules from one part of a material to another.
• Hot liquids & gases rise while cold ones fall. This creates currents that carry the heat energy
• Wind is caused by convection
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Good and Poor Conductors
• Poor Heat Conductors- Wood- Plastic- Glass- Gases
• Good Heat Conductors-Most metals
Conductors: material that easily transfers heat
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Insulation• Insulation: is used to reduce the amount of
heat loss by conduction• Poor Conductors are good insulators• Materials that trap air are good insulators
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DO NOT WRITEHeat Transfer
• Used in heating systems of homes and other buildings• Used in Cooling Systems too
• Heating• Fireplace-Radiation• Steam Heating-Uses all 3• Hot Water Heating-Uses all 3• Electrical• Solar
• Cooling• *Uses evaporation to absorb heat• Air Conditioners• Refrigerators
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Heating an Object• Specific Heat: This is the amount of heat
needed to raise the temperature of 1 kg of a substance by 1 Degree Celsius (depends on the material)
• Thermal Equilibrium: This is when there is no heat movement between two things, because both objects have reached an equal amount of thermal energy.
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Three Laws of Thermodynamics
• First Law of Thermodynamics: Aka> The Law of Conservation of Energy. The amount of energy in the universe remains constant.
• Second Law of Thermodynamics: Any process will tend to increase the amount of entropy (chaos) in the universe!!!!
• Third Law of Thermodynamics: As the temperature approaches absolute zero, the entropy of a system approaches its minimum.