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Transcript
Slides possibly useful for OP2
Humans & Energy
• “…the single most important distinction
[between humans and other animals] is that
we make significant use of energy beyond
what our body’s own metabolism provides.” p.
16
Human Energy Use
•
•
•
•
•
Manufacture goods
Live comfortably/heat or cool
Transport goods and ourselves
High-speed communication
Industrial agriculture
Earth’s “Energy Endowment”
• “A realistic picture of the Earth’s energy endowment, then,
is this: we have available a substantial, continuous energy
flow from the Sun, and much lesser flows from Earth’s
interior heat and from the tidal energy of the Earth-Moon
system. Inside the Earth we have fossil fuels, which we’re
quickly depleting, and the nuclear fuels uranium and
thorium which we know how to exploit. We also have a vast
nuclear fuel resource in the hydrogen of seawater, but
when and if we’ll ever learn to use that one is a wide open
question. That’s it. When we talk about ‘energy
alternatives,’ ‘renewable energy,’ and other popular
solutions to energy-related environmental problems,
there’s no new, hidden, as-yet-undiscovered source. We
either have to turn to one of the known sources that
comprise Earth’s energy endowment, or we have to use
less energy.” p. 15-16
History of US Energy Consumption in the US,
1775-2001 (Quadrillion Btu, 1015 Btu)
100
Nuclear Electric Power
80
60
Natural Gas
Petroleum
Coal
40
Hydroelectric Power
20
0
Wood
Your (North American) Energy Use
• Rate of 10 kW
• = 10,000 Watts
• = 100 times our body output
At what rate do you as a citizen of the 21st
century industrialized society, use energy?
How does that compare to the rest of the
world’s population?
US energy consumption
US Energy Flows
US Energy Sources
World Energy Sources
http://blogs.edf.org/climate411/wp-content/files/2007/07/ElectromagneticSpectrum.png
Energy Quality and Usefulness
• How easy/hard is it to harness the energy?
–
–
–
–
–
Car?
Gasoline?
Heated water?
Oreo?
Kneebends?
• Can that energy be completely returned?
(Irreversibility)
Useful Energy
The Thermos…
Paul Hewitt, Conceptual Physics, 10th edition
Coal Formation
•
http://www.classzone.com/books/earth_science/terc/content/visualizations/es0701/es0701page01.cfm?c
hapter_no=visualization
• “So, coal’s energy is ultimately sunlight energy
trapped by long-dead plants. This direct link
with once-living matter makes coal a fossil
fuel.” (p. 106)
Oil and Natural Gas Formation
• http://www.green-planet-solarenergy.com/fossil-fuel-formation.html
• http://vodpod.com/watch/1029812-oil-andnatural-gas-formation
Oil and Natural Gas Formation
Oil and Natural Gas Formation
• http://www.green-planet-solarenergy.com/fossil-fuel-formation.html
• http://vodpod.com/watch/1029812-oil-andnatural-gas-formation
Oil and Natural Gas Formation
Petroleum Refining
• http://science.howstuffworks.com/oilrefining4.htm
Where do these petroleum distillates go?
History of fossil fuel use
Combustion
• Different relative amounts of CO2 produced
• Reaction is exothermic: bonds are broken,
reformed, and energy released as a result
• http://schools.matter.org.uk/Content/Reactio
ns/BondActivation.html
• Combustion can be more or less efficient,
more or less ‘clean’ – there are lots of
byproducts
Combustion
• Combustion increases the amount of
greenhouse gases in our atmosphere; the
relative amount of CO2 produced
depends on what fossil fuel was burned
• Combustion also produces byproducts
from impurities in fossil fuels
• How do we harness the energy released
during combustion to make it useful for our
needs?
From fossil fuel to useful energy
• Can use the thermal energy produced from
combustion to heat other substances – water, air,
etc.
• Can try to transform the thermal energy released
during combustion into more high-quality forms of
energy, like electricity or motion (kinetic energy)
– But remember, the Second Law of Thermodynamics tells
us that we can’t change ALL of the low-quality combustion
E into high-quality E
Examples of lifting work, pulling work or no work
done…
atlas stones
barrel hold
truck pull
• Atlas stones:
– Work done when lifting
• To calculate, would need to find mass of the boulder and height it
was lifted; W = Fd = ∆PE = mgh
– No work done when carrying the boulder (force applied is
at right angles to the motion)
• Barrel hold:
– No work done! Nothing is moving.
• Truck pull:
– Work done when pulling
• To calculate, would need to find the mass of the truck and the
speed (velocity) at which it is moving, OR the force applied by the
man and the distance he pulls the truck; W = Fd = ∆KE = 1/2mv2
A small puzzle…
• Recall from earlier: Forces can act on a mass
to give it kinetic energy, or masses can move
against a force and will have potential energy
as a result
• Atlas stone on top of the pillar still has
potential energy, but truck at end of truck pull
doesn’t have kinetic energy (it stops moving) –
WHY?
Friction!
• The kinetic energy given to the truck by the
work the man did on it was converted to
thermal energy (“heat”) because of the
friction between the truck and the ground…
• We’ll have much more to say about the
invidious effects of friction on energy
production and use (i.e., energy
transformation) throughout this course