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   Back-of-envelope Physics
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Proposal for a part III course (also open to part II students).

Aims
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1. To consolidate and enhance the essential Physicist's skills of
   approximation and estimation.
2. To connect together the courses studied in Cambridge into a unified
   toolbox useful for analysing anything.
3. To relate Physical principles to the real world and explore
   important issues facing society today.

Personnel
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David MacKay; perhaps also Richard Friend and Richard Hills?

Teaching method
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Interactive lectures with a large element of group work.
Two 90-minute lectures per week.

Timing
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Probably 11am Tuesday, Friday, in order to align with the
part III revision classes, starting in week 1 or 2.
(Or perhaps start only after projects are handed in?)
Number of sessions: 4-6, each lasting 90 mins. 

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Sketch of a few lecture topics relating to Energy.
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[Each of the following four items would occupy at least one 90-minute session.]

1. Energy basics
 - Energy in a Mars bar
 - Energy in a 1.5V battery
 - heat capacity of water
 - light
 - sound (amplitude of sound waves; power required for a stereo)


2. Energy consumption
     (Aim: estimate total energy consumption of a typical European,
      and understand what it's dominated by)
  - Immediate, local, daily personal energy use
   -- Food
   -- Cooking
   -- Heating
   -- Hot water
   -- Transportation

  - Energy use caused remotely or occasionally
   -- Garbage disposal
   -- Food production
   -- Production of manufactured goods
         (eg Aluminium cans, cars)
   -- Transportation of food and goods
   -- Buildings (creation of)

3. Look at Transportation in detail:
  - Where does the energy go? How does drag work? Dimensional analysis.
  - Estimate the power costs of
      riding a bike,
      driving a car,
      flying a plane,
      riding a train.
  - Find scaling of car power with velocity.
  - What's the essential physics of flight? How do the energy costs of drag
     and lift-production scale with velocity and plane/bird dimensions?
  - How far can a bird fly? (Or a plane.)

4. Energy harvesting.
  - Having estimated the total energy consumed by one European, ask
    the question: where is the energy to come from, if we are to live
    sustainably?
   
      - Energy flux of wind
      -             of sunshine
      -             of tidal flow
      -             of geothermal energy
      -             of waves
      -             of rivers

   Power of a 50-m windmill; land area occupied;
                associated costs of production and maintenance.
   Power of a tidal power station; area occupied; associated costs.
   Power of a biomass-powered thermal power station; area occupied; associated costs.
   Power of a photovoltaic array; area occupied; associated costs.
 Similarly....
   Wave power.
   Hydroelectric.
   Solar-thermal generation.

   Which of these sources can sustain the European energy consumption
   computed in the previous lecture? What density of windmills would
   be needed in England? If we use biomass, would there be any space
   left for people?

   What is the efficiency of a windmill?

   What is the maximum possible efficiency of a photovoltaic system?
     (see www.inference.phy.cam.ac.uk/sustainable/solar/ for a
      superb analysis by John Hopfield)

   What is the efficiency of a plant in capturing sunlight? And in turning
      it into chemical energy? What principles of device physics are
      common between plants and Silicon-based photovoltaics?

  - Conclusion: Choices available to society
	-- Invest in research in making photovoltaics cheap
	-- Reduce consumption
	-- Reduce population
	-- World War III