Transcript Ch 7

Chapter Seven
 Section 1
 Section 6
 Section 2
 Section 7
 Section 3
 Section 8
 Section 4
 Formulas
 Section 5
Heating
 Any flow of thermal energy from a higher to a
lower temperature is called heating.
 Temperature is a quantitative measure of
warmth as measured by a thermometer.
 The Law of Heating: Thermal energy flows
spontaneously from higher to lower
temperature, but not from lower to higher
temperature.
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Heat Engines: Using Thermal
Energy to Do Work
 A heat engine is any cyclic device that uses
thermal energy to do work. Its energy
efficiency, the fraction of its input thermal
energy that is converted to work, will be
higher if the input temperature is higher and
the exhaust temperature is lower.
 A heat engine’s ejected thermal energy is
called exhaust.
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Energy Quality: Things Run
Down
 Thermal energy is considered to be of lower
quality than other energy forms, because of
the second law’s restrictions on converting it
to other forms.
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The Law of Entropy: Why You
Can’t Break Even
 Entropy is the measure of microscopic
disorganization, the disorganization on a
microscopic scale.
 The Second Law of Thermodynamics: The
total entropy of all the participants in any
physical process cannot decrease during that
process, but it can increase.
 Entropy cannot be decreased.
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The Automobile
 Internal combustion engines burn a fuel-air
mixture. The high combustion temperature
gives it a high pressure, so that hot gases can
push strongly on a piston, a movable metal
plate connected to a rod.
 Diagram
 External combustion occurs in a fuel that then
provides thermal energy to a second
substance that does the actual work
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Diagram
Transportation Efficiency
 Transportation efficiency is useful output,
such as distance traveled, passengers moved
or freight moved, per unit of fuel input.
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The Steam-Electric Power
Plant
 A steam turbine is a large rotating device that
turns when it feels a higher pressure on the
front side than on the back.
 The turbine turns an electric generator that
creates electricity when the turbine causes it
to rotate.
 Diagram
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Diagram
Resource Use and Exponential
Growth
 A non-renewable is a resource that cannot be
readily replaced within a human lifetime.
 Renewable resources, such as wood or solar
energy, can be sustained indefinitely,
assuming they are consumed at less than the
replacement rate.
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Formulas
 ThermE (input) -> Work + Therm E (exhaust)
 Energy Efficiency = work output
thermal energy input
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