Thermal Energy

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Thermal Energy
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Warm Up

• To shape metal into a horseshoe, the metal is
  heated in a fire. Why will a horseshoe bend when
  its very hot, but not after it cools?

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What was different ?

• Matter is always in motion
• Particles of gases, liquids, and solids all
  move

• There was more motion in the hot water

• The energy of motion is Kinetic Energy

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Heat

• Heat is the transfer of thermal energy from one
  object to another because of a temperature
  difference.
• Heat flows spontaneously from hot objects to cold
  objects.

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Heat
Heat is related to temperature The Temperature
of an object is the measurement of the average
kinetic energy (KE) of particles
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• As an object heats up its particles move
  __________________ on average. As a result, the
  average kinetic energy (and the temperature)
  _________________.
• Number of collisions between particles
  increases. Thermal energy is transferred from
  hot to cold objects.

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What do Temperature Scales Measure?

• Fahrenheit used in US
• Celsius used in other countries
• Kelvin SI unit
• 0 K -273C
• 0C 273 K

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Thermal Energy

• Thermal Energy (Q) is the sum of the kinetic
  energy the potential energy of all the
  particles in an object
• Thermal energy depends on the mass, temperature
  and phase (solid, liquid, or gas) of an object.

Q KE PE
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Thermodynamics

• First Law of Thermodynamics the increase in
  thermal energy of a system equals the work done
  on the system plus the heat transferred to the
  system

• Energy is CONSERVED

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Open Systems

• In an open system, heat flows across the
  boundary, or work is done across the boundary.
• What are examples of open systems?

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Closed Systems

• In a closed system, no heat flows across the
  boundary and no work is done across the boundary.
• What are examples of closed systems?

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Thermodynamics

• Second Law of Thermodynamics Heat flows from
  warmer objects to cooler objects
• Heat cannot flow from a cooler object to a
  warmer object unless work is done

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How do solids transfer heat?

• Conduction the transfer of thermal energy by
  collisions between particles in matter.
• Particles in solids vibrate and collide with each
  other

• List 3 examples of conduction

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Convection

• Convection is the transfer of thermal energy in a
  gas or liquid by the movement of warmer and
  cooler fluid from place to place.

• Knowing this, what will happen to a piece of ice
  floating at the top of a warm glass of water?
• What will happen to a piece of ice at the bottom
  of a glass of water?
• List 3 examples of convection

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Radiation

• Radiation is the transfer of energy by
  electromagnetic waves. These waves travel in the
  empty spaces between particles until their energy
  is absorbed by a particle.
• Would radiation pass through a solid or a gas
  more easily?

• List 3 examples of heat radiation.

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Heat

• Heat is the thermal energy that is transferred
  from particles at a higher temperature to
  particles at a lower temperature

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Can you control heat flow?

• An INSULATOR is a material in which heat flows
  slowly
• Good Insulators plastic, wood, air, fiberglass
• Materials that arent good insulators are
  CONDUCTORS. Heat flows quickly through a
  conductor.
• Good Conductors
• metals

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What if there is no material?

• There is no conduction if there is no matter. A
  vacuum (empty space) is a perfect insulator
  because very little heat transfer can take place.

• We use vacuum insulators and air insulators all
  the time. List some examples.

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How is the water inside being heated?
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