Heat

1
Heat

• Chapter 10

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Defining Temperature

• Temperature is defined as a measure of the
  average kinetic energy of the particles in a
  substance.
• Temperature measures energy
• Energy must be either added or removed to change
  temperature.

3
Defining Temperature

• A has a low kinetic energy so it has a low
  temperature. Energy is added to B, thus it has
  a higher temperature.

4
Defining Temperature

• The energies associated with atomic motion are
  referred to as internal energy.
• Internal energy depends on the size of the
  sample.
• Big sample more atoms more internal energy

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Thermal Equilibrium

• Thermal equilibrium is the state in which two
  bodies in physical contact with each other have
  identical temperatures.
• Ex Hot liquid cocoa cold milk lukewarm drink

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Converting Temperature Units

• Celsius to Kelvin
• TK TC 273
• Kelvin to Celsius
• TC TK - 273

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Defining Heat

• Heat the energy transferred between objects
  because of a difference in their temperatures

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Units of Heat Energy

• SI unit joule (J)
• Other units are
• Calorie (cal),
• Kilocalorie (1000 cal),
• British thermal unit (Btu)
• and therm (100,000 Btu)

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Conservation of Energy

• Conservation of Energy if changes in internal
  energy are taken into account with changes in
  mechanical energy, the total energy is a
  universally conserved property.

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Conservation of Energy

• Conservation of Energy
• ?PE ?KE ?U 0
• OR
• PEi KEi Ui PEf KEf Uf

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Example

• A vessel contains water. Paddles that are
  propelled by falling masses turn in the water.
  This agitation warms the water and increases its
  internal energy. The temperature of the water is
  then measured giving an indication of the waters
  internal energy increase.

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Example

• If a total mass of 11.5 kg falls 1.3 m and all of
  the mechanical energy is converted to internal
  energy, by how much will the internal energy of
  the water increase?

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Solution

• ?PE ?KE ?U 0
• PEi KEi Ui PEf KEf Uf
• PEi mgh
• Mgh 0 Ui 0 0 Uf
• ?U Uf - Ui mgh
• ?U (11.5 kg )(9.81 m/s2)(1.3 m)
• ?U 1.5 x 102 J

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Specific Heat Capacity

• Specific heat capacity the quantity of energy
  needed to raise the temperature of 1 kg of a
  substance by 1? C at constant pressure
• Air 1.01 X 103 J/kg?C
• Water 4.19 X 103 J/kg?C

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Ultimately

• The higher the specific heat capacity, the less
  change you will see in the temperature of that
  substance under similar conditions
• Temp of Sand vs Water on a Hot Day

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• Thermal conductors transfer energy as heat
  rapidly
• Thermal insulators slowly transfer energy as
  heat
• Conduction Transfer of energy through matter by
  colliding particles solid to solid contact
• Convection - Transfer of energy by the motion of
  heated particles in a gas or liquid
• Radiation - Transfer of energy in the form of
  electromagnetic waves (no contact)

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Homework

• P 363 4-5
• P 370 1, 2, 5
• P 385 1-3