The Physics of Rubber Bands

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The Physics of Rubber Bands
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What do rubber bands and springs have in common?
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What do rubber bands and springs have in common?

• Exert a restoring force proportional to the
  displacement from equilibrium

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How are they different?
D
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How are they different?

• Rubber breaks cleanly

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How are they different?

• Rubber breaks cleanly
• Spring-like nature not destroyed by overextension

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How are they different?
D

• Rubber breaks cleanly
• Spring-like nature not destroyed by overextension
• Temperature changes with extension/relaxation

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Why does rubber behave as it does?
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Why does rubber behave as it does?
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Why does rubber behave as it does?
S
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Other examples of random motion
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Other examples of random motion

• Scent expanding in air (gaseous mixture)

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Other examples of random motion

• Scent expanding in air (gaseous mixture)
• Food coloring expanding in water (aqueous mixture)

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Characteristics of random motion
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Characteristics of random motion
D

• Random motion will lead to the most probable state

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Characteristics of random motion
D

• Random motion will lead to the most probable
  state
• The rate of random motion is temperature dependent

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Why does rubber warm when stretched and cool when
relaxed?
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Why does rubber warm when stretched and cool when
relaxed?

• When rubber is relaxed it has lots of internal
  freedom

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Why does rubber warm when stretched and cool when
relaxed?

• When rubber is stretched it has limited
  internal freedom

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Why does rubber warm when stretched and cool when
relaxed?

• Stretching a rubber band restricts the random
  rotations

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Why does rubber warm when stretched and cool when
relaxed?

• Stretching a rubber band restricts the random
  rotations
• The energy that was involved in the random
  rotations gets converted into random vibrations
  and the band heats up

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Why does rubber warm when stretched and cool when
relaxed?

• Conversely, it takes energy to start the random
  rotations when a stretched band is released

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Why does rubber warm when stretched and cool when
relaxed?

• Conversely, it takes energy to start the random
  rotations when a stretched band is released
• The energy for the random rotations comes from
  the vibrational energy of the band and the band
  cools off

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Why does rubber warm when stretched and cool when
relaxed?

• Energy is conserved

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How might this property be useful?
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How might this property be useful?

• Refrigeration