Thermal Expansion

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Thermal Expansion
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• When an object is heated, it expands.
• When object is cooled, it contracts.
• This is known (to physics-types) as THERMAL
  EXPANSION.
• This occurs because
• When the temperature of a substance changes, the
  energy that is stored in the intermolecular bonds
  between atoms changes. When the stored energy
  increases, so does the length of the molecular
  bonds.
• OR (in English)as temperature increases
  molecules move faster (have a greater average
  translational KE) and move farther apart

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Examples of Thermal Expansion

• Metal framed windows need rubber spacers
• Metal hot water heating pipes should not be used
  in long straight lengths
• Large structures such as railways and bridges
  need expansion joints in the structures to avoid
  sun kink.
• Thermometers are another example of an
  application of thermal expansion
• most contain a liquid which is constrained to
  flow in only one direction (along the tube) due
  to changes in volume brought about by changes in
  temperature

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Strange Thermal Expansion

• Water contradicts this idea when it is heated
  from 0C to 4C it actually CONTRACTS.
• Water is the most dense at 4C!
• This is why fish can live in a lake that has ice
  on top the water at the bottom is 4C.

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Thermal Expansion Formulas

• Linear ?L Loa ?T
• Area ?A 2Aoa ?T
• Volume ?V 3Voa ?T or ?V Voß ?T
• How much taller is the Eiffel Tower on the
  hottest day of the summer (25 C) than the
  coldest day of the winter (2 C)? The tower is
  324 m tall measured (on the coldest day) from the
  top of the flagpole. Assume the tower is built of
  structural steel a 12 x 10-6 C-1.