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Where does all E end up?

  • Thermal E = the eventual fate of all energy is to end up as thermal.

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  • The universe should get hotter and hotter, and energy should spread out evenly
  • Impossible to get 100% of thermal E converted back into another form
    • (100% efficiency impossible)
    • Perpetual motion impossible!!!
    • No free energy!

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Chemical PE in your food

  • Measured in Calories (4184 J = 1 C)
  • Calorie (kilocalorie) = 1000 calories

Different types of food have diff. E per unit mass

FATS 9 Cal / gram

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CARBOHYDRATES 4 Cal/g

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PROTEIN 4 Cal/g

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(Alcohol) 7 Cal/g

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Practice

  • How many Joules in a 100 Calorie snack?

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  • How many Calories in a shake that has:
      • 5g sugar (carbohydrate),
      • 15g fat,
      • 1g protein

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Practice

  • A candy bar has 10g of fat, 5g protein, and 20g carbs.
  • How many Calories from fat?
  • How many total Calories?

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  • How many candy bars would you need to give you your daily requirement? (~2000 Calories/day)

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Nuclear Fission/Fusion

    • Mass = Energy
  • Fission: atom breaks apart into two pieces → mass disappears
    • Harnessed by Man – nuclear power plants and bombs

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  • Fusion: two atoms combine into one → mass disappears
    • Only happens in stars and bombs – humans still trying to harness/sustain/control Fusion.