Chapter 9 - Thermal Energy

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Chapter 9 - Thermal Energy

• Sections 9.1, 9.2, 9.3

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Objectives

• By the end of class today, you will be able to
• Define and describe thermal energy
• Describe the relationship between temperature and
  kinetic energy
• PS F-11, 15, 17

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9.1 - Thermal Energy

• All matter is made up of constantly moving atoms
  or molecules
• The motion of a substances molecules determines
  if it is a solid, a liquid, or a gas
• When molecules are made to move faster, they gain
  kinetic energy.

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9.1 - Thermal Energy

• In general, the warmer an object is, the more
  kinetic energy its atoms and molecules possess.
• We can also say that the warmer an object gets,
  the more thermal energy it contains.

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9.1 - Thermal Energy

• What is thermal energy?
• The total energy of all an objects atoms and
  molecules
• Thermal energy consists of both the potential and
  kinetic energy of the particles in a substance as
  they move around.

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9.2 - Temperature

• Why do we measure an objects temperature?
• To be able to tell how warm or cold it is.
• A thermometer measures by expansion or
  contraction of a liquid, usually colored alcohol.

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9.2 - Temperature

• Temperature Scales -
• Celsius Scale - O is the freezing point of H2O
  and 100 is the boiling point of H2O.
• Fahrenheit Scale - 32 is the freezing point of
  H2O and 212 is the boiling point of H2O.

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9.2 - Temperature

• Temperature is related to the random motion of
  atoms/molecules in a substance.
• Temperature is related to the average KE of
  molecular motion.
• A substance with a high temperature has molecules
  with high average KE
• The molecules are moving very fast if the object
  has a high temperature

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Which box has a larger temperature?
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9.2 - Temperature

• Concept Check Question
• True or False -
• Cold is the absence of moving molecules.
• False!
• Cold refers to very-slow moving molecules, not
  their absence. Without molecules, the concept of
  temperature is meaningless!!!

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9.3 - Absolute Zero

• In principle, there is no upper limit to
  temperature.
• As thermal energy keeps increasing, a solid
  object melts to a liquid and then evaporates into
  a gas.

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9.3 - Absolute Zero

• However, there is a definite limit at the lower
  end of the temperature scale.
• This limit is called absolute zero!

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9.3 - Absolute Zero

• In degrees Celsius, this temperature is -273!
• At this temperature, molecules have lost all
  available KE.
• No more energy can be taken from a substance at
  absolute zero.
• It cant get any colder!!!!

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9.3 - Absolute Zero

• The absolute temperature scale is called the
  Kelvin scale.
• Absolute zero is 0 K. (Kelvin)
• There are no negative numbers on the Kelvin scale.

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References

• http//cse.ssl.berkeley.edu/bmendez/ay10/2002/note
  s/pics/bt2lf0403_a.jpg
• http//www.pa.msu.edu/sciencet/images/AbsoluteZero
  .jpg