Temperature, Heat

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Temperature, Heat Expansion
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• Temperature - The quantity that tells how hot or
  cold something is compared with a standard.
• Measuring temperature
• A common thermometer measures temperature by
  showing the expansion contraction of a liquid
  in a glass tube using a scale.
• the liquid is usually mercury or colored
  alcohol

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Temperature Scales

• Celsius
• - most widely used scale
• - international scale
• - 00c temperature at which water freezes
• - 1000c temperature at which water boils
• Fahrenheit
• used commonly in the U.S.
• 32o temperature at which water freezes
• 212o temperature at which water boils
• Kelvin
• used in scientific research
• degrees are the same as Celsius and are called
  Kelvin
• 0oK absolute zero (0oK -273oC)
• Absolute zero is the temperature at which a
  substance has NO kinetic energy.

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• Temperature is proportional to the average
  kinetic energy.
• As temperature increases kinetic energy
  increases.

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Heat

• Heat the energy that transfers from one object
  to another because of a temperature difference.
• HEAT IS ENERGY
• Heat is energy in transit from a body of higher
  temperature to one of lower temperature
• The energy resulting from heat flow in Thermal
  energy.

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Thermal Equilibrium

• What is thermal equilibrium???
• When objects in thermal contact with each other
  reach the same temperature and no heat flows
  between them.
• ex to read a thermometer we wait until the
  liquid stops moving. This is the point when the
  liquid in the thermometer and the substance
  being measured have reached thermal equilibrium.

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Internal Energy

• The grand total of all energies in a substance
  is the internal energy.
• A substance does not contain HEAT, it contains
  ENERGY !!!
• This includes
• The KE of moving molecules and atoms of a
  substance.
• The PE due to the forces between molecules or
  atoms.

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Measuring Heat

• Heat is measured in calories.
• A calorie the amount of heat required to raise
  the temp. of 1g water, 1oC.
• A kilocalorie 1000 calories
• Kilocalories are the heat unit used in rating
  foods. Kilocalories are often referred to as
  Calories. (with a capitol C)

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Specific Heat Capacity

• Specific heat is the quantity of heat required
  to raise the temp. of a unit of mass of a
  substance by 1 degree.
• Different substances have different capacities
  for storing internal energy
• (re ability to hold heat)
• and
• require specific quantities of heat to raise the
  temp. of a given mass a specific number of
  degrees.

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Example

• 1g of water requires 1 calorie to raise the
  temp. 1oC.
• WHILE
• 1g of iron requires 1/8 as much energy to raise
  the temp. 1oC.
• Water absorbs more heat per gram that iron for
  the same temperature change.
• So water has a higher Specific Heat.
• (BTW water is considered to have a very high
  sp.heat)

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Thermal Expansion

• When the temp. of a substance increases the
  molecules move faster (increase KE)
• This results in the EXPANSION of the substance.
• With few exceptions all forms of matter (solid,
  liquid gas) expand when heated
• and
• contract when cooled.

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Heat Transfer

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Conduction

• Conduction heat transfer within and between
  different materials in direct contact. (molecule
  to molecule)
• conductor material that conducts heat well
  (metal)
• insulator material that delays the transfer of
  heat (wood)

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• Poor conductors good insulators
• Good conductors poor insulators
• Which feels colder barefeet on tile or carpet?
• The tile because it is a good insulator. The
  heat moves from your feet to the tile.
• Does a blanket make you feel warmer?
• The blanket is a good insulator and delays the
  transfer of heat from your body to the air.

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Convection

• Convection is when heat is transfer through a
  current in a fluid.
• fluids can be either liquids or gases
• examples
• - Air in contact with a hot stove rises and
  warms the region above.
• Water boils through convection
• convection currents stir our atmosphere

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Radiation

• Radiation is the transfer of heat through
  electromagnetic waves. (UV light, visible light,
  infrared, microwaves, radio waves, etc.)
• Examples
• The sun
• a lightbulb
• a fireplace
• Any energy, including heat, that is transmitted
  by radiation is called radiant energy.