Notes on Energy and Power

Chapter 1: Energy and Power and the Physics of Explosions

• Definition of Energy:

  • Energy is the ability to do work.
  • It must be conserved; it cannot be created or destroyed.
  • Energy can transform into different forms (e.g., heat, chemical, mechanical).
  • Summary: Energy is fundamental for existence and the functioning of the Earth.

• Measuring Energy:

  • Different units are used in various fields:
  • Chemistry/Biology: Calorie (cal) and kilocalorie (Cal)
    • 1 Cal = 1000 cal = energy to raise 1g of water by 1°C.
  • Industry: Kilowatt-hour (kWh)
    • 1 kWh ≈ 1000 Cal = 3.6 million J.
  • Physics: Joule (J)
  • Example: One can of soda contains:
  • 150 Cal = 150,000 cal = 0.150 kWh = 630,000 J.

• Average Household Energy Use:

  • Approximately 12,000 kWh/year, equivalent to:
  • ~80,000 cans of soda (150 Cal each)
  • ~120,000 bananas (100 Cal each)
  • ~2,000,000 grams of coal
  • ~360 gallons of gasoline.

• Examples of Energy Consumption:

  • Breakdown of common household appliances:
  • 16 W bulb: 4.8 kWh/month (57.6 kWh/year)
  • 100 W bulb: 30 kWh/month (360 kWh/year)
  • Refrigerator: 36.7 kWh/month (440 kWh/year)
  • Dishwasher: 41 kWh/month (492 kWh/year)
  • Clothes Washer: 24.9 kWh/month (299 kWh/year)
  • Electric Clothes Dryer: 74.7 kWh/month (896 kWh/year)
  • Self-cleaning Stove & Oven: 61.25 kWh/month (735 kWh/year).

• Concept of Power:

  • Defined as the rate at which energy is used (energy over time).
  • Power measured in Joules per second (J/s) or Watts (W).
  • Examples of Power Consumption:
  • 1 watt = 1 Joule/s (e.g., flashlight)
  • 100 watts = bright light bulb (heat from human body)
  • 1 horsepower (hp) ≈ 1 kilowatt (kW)
  • 1 megawatt (MW) = 1 million watts (power for a small town).

• Energy Density Comparison:

  • Energy content per gram for various materials:
  • TNT (trinitrotoluene): 0.65 Cal/g = 2,723 J/g
  • Coal: 27,000 J/g
  • Gasoline: 42,000 J/g.
  • Notable: Uranium-235 has approximately 30 million times more energy density than TNT.

• Chemical Energy Transfer:

  • Energy transfer in chemical reactions is critical in explosive reactions (TNT vs. Food).
  • Batteries: Lower energy density compared to gasoline but advantageous for portability.

• Electric vs. Gasoline Vehicles:

  • Electric cars derive power from various energy sources (often fossil fuels).
  • Emission comparisons:
  • Coal: 0.23 lbs/MJ
  • Gasoline: 0.16 lbs/MJ.

• Energy Generation Methods:

  • Steam Engine: Traditional method for energy transfer; used in boats and trains.
  • Coal: Significant CO2 emissions; primary energy source in the US and China.
  • Nuclear Power: Low waste but long-lived radiation; potential for Generation IV reactors.
  • Hydroelectric: Uses river water to power turbines; consistent energy supply but environmental concerns.
  • Geothermal: Uses Earth's heat for steam; produces about 0.8 TWh/year.
  • Solar Power:
  • Concentrated solar: Boils water to generate electricity.
  • Photovoltaic panels: Convert sunlight to electricity (requires significant space).
  • Natural Gas: Primarily used via combustion; produces lower emissions compared to coal.
  • Wind Power: Generated through wind turbine movement; low land impact but intermittently available.

• Key Insights on Energy Use:

  • Energy consumption is projected across various sectors and is crucial for economic growth.
  • The effectiveness of renewable energy sources remains complex, considering efficiency and cost of energy extraction and transformation.

• Energy Takeaways:

  • Energy is a critical component of work and life.
  • Energy can be harnessed through multiple means.
  • Storage of energy presents significant challenges.
  • Understanding energy systems is vital for addressing climate change issues.