Energy: Theory, History, Use

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Energy is an abstract quantity, the capacity for doing work, that retains the same value through changes of its forms.

Richard Feynman on Energy

“It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. However, there are formulas for calculating some numerical quantity, and when we add it all together it gives “2828”—always the same number. It is an abstract thing in that it does not tell us the mechanism or the reasons for the various formulas.”

Theory of Energy
  • Forms of Energy
  • Formulas
  • Two Basic Forms
  • Pendulum
  • Work and Heat
  • Law of Conservation of Energy

View Theory of Energy

  • Zeroth Law
    • If two systems are in thermal equilibrium with a third, they are in thermal equilibrium with each other.
  • First Law
    • The change in a system’s internal energy equals the heat added to the system from its surroundings minus the work done by the system on its surroundings.
  • Second Law
    • The entropy of an isolated system either increases or stays the same.
  • Third Law
    • The entropy of an isolated system nears zero as its temperature approaches absolute zero.

View Thermodynamics

History of Idea of Energy
  • From Afterthought to Alternative to Central Role
  • Timeline

View History of Idea of Energy

Sources of Energy
  • Primary Sources
    • Non-Renewable
    • Renewable
  • Secondary Sources
    • Electricity
    • Hydrogen

View Sources of Energy

Energy Conversion

View Energy Conversion

Units of Power and Energy
  • Energy and Power
  • Units of Energy
  • Units of Power
  • Calculators

View Units of Power and Energy