Some Basic Concepts of Energy

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Some Basic Conceptsof Energy
II. Concepts relating to heat
Prepared for BIO/EES 105 Energy in our World

• Kenneth M. Klemow, Ph.D.
• Wilkes University

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Temperature and heat

• Property of all systems
• Based on kinetic energy of molecules
• Heat is TOTAL energy of all molecules in a system
• Typically measured in Calories or BTUs
• Temperature is AVERAGE energy of all molecules in
  a system
• Typically measured in degrees

Fahrenheit Celsius Kelvin
Water freezes 32 0 273
Water boils 212 100 373
Human body 98.6 37 310
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Temperature vs heat within and between systems

• Within a system
• Increase in heat causes increase in temperature
• Governed by equation

Q mc(DT) Where Q heat (cal., BTU) M
mass C specific heat DT change in temp.
http//www.thekitchn.com/thursday-giveaway-instant
read-56533
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Temperature vs heat within and between systems

• Between systems
• Not related
• One system can have higher heat yet lower
  temperature

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Temperature vs heat within and between systems

• Heat can move from one system to another
• Only when there is a temperature difference
• Move from higher temperature to lower temperature
  object.

http//www.ces.fau.edu/nasa/
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Another way to look at heat transfer
http//www.grc.nasa.gov/WWW/Wright/airplane/heat.h
tml
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Specific heat (c)

• Measure of change in temperature as a result of
  heat absorbed.
• Metric system joules needed to raise 1 kg of
  material by 1 oC.
• English system BTUs needed to raise 1 lb of
  material by 1oF.

http//addheat.wordpress.com/2011/03/24/
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Examples of specific heats of different substances
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Heat of vaporization and heat of fusionInvolves
phase changes
http//blogs.yis.ac.jp/19miyoshiay/
http//ww.abc6.com/story/
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Heat of vaporization and heat of fusion

• Heat absorbed or released depending on direction
• Important in heat balance at earths surface,
  regulating temperatures of organisms

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Temperature as a function of heat in water
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Forms of heat transfer
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Conduction

• Energy of molecules directly transferred to
  adjoining molecules
• Causes them to gain heat

http//www.physicstutorials.org/
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Conductivity differs among materials
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Conductive heat transferthrough a material
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Convection

• Occurs in liquids and gases
• Warm liquid / gas becomes less dense and rises
  through medium
• Creates eddy currents
• Carries much energy

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Radiation

• Involves electromagnetic waves
• Produced by charged particles
• Travel at speed of light
• Wave components include
• Amplitude
• Frequency
• Wavelength
• Electric and magnetic waves are perpendicular to
  field of travel

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Frequency and wavelength are inversely related

• Velocity (m/s) wavelength (m) x frequency
  (/second)
• As wavelength increases, frequency decreases

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Radiation is classified by wavelength (and hence
by frequency)
More energy
Less energy
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Thought questions

• When radiation strikes a body, it causes that
  body to start radiating, itself.
• Will the wavelengths of that energy likely to be
  longer or shorter than the energy striking it?
• When sunlight hits the earth, will the
  re-radiated energy be more likely to be in the
  form of
• Ultraviolet, Visible, Infrared energy
• When light strikes a chlorophyll solution, some
  of the energy is reradiated as visible light.
  What is the most likely color for that light?
• Blue, Green, or Red

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Need to mention boundary layer effects

• Conduction, convection and radiation all occur in
  windless environment.
• Convection sets up eddies of moving air
• Adding wind can rapidly remove energy by mass
  transfer.
• Objects often covered by boundary layer of still
  air
• Conduction and convection predominate
• Increasing wind speed causes boundary layer to
  become thinner.
• Transfer of energy greater when wind increases