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)

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?chapter_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-solar-energy.com/fossil-fuel-formation.html

• http://vodpod.com/watch/1029812-oil-and-natural-gas-formation

Oil and Natural Gas Formation

Oil and Natural Gas Formation

• http://www.green-planet-solar-energy.com/fossil-fuel-formation.html

• http://vodpod.com/watch/1029812-oil-and-natural-gas-formation

Oil and Natural Gas Formation

Petroleum Refining

• http://science.howstuffworks.com/oil-refining4.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/

Reactions/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