Energy

Summary

• Definition
  • A system possesses energy if it has the ability to do work.
• Energy…
  • is an abstract scalar quantity
  • is a quantity that an object or system of objects is said to possess
  • is not a thing that can be measured
  • is a quantity that acquires meaning only through computation
• Forms
  • Potential energy
    • Definitions
      • energy due to arrangement
      • energy due to position (of a quantity in a field)
    • Types
      • gravitational potential energy
      • electromagnetic potential energy
        • electric potential energy
        • magnetic potential energy
        • chemical potential energy
        • elastic potential energy
      • strong nuclear potential energy
      • weak nuclear potential energy
  • Kinetic energy
    • Definition
      • energy due to motion
    • Types
      • mechanical energy: macroscopic motion
      • thermal energy (heat, internal energy): random motion of microscopic particles
      • electric energy: bulk flow of charged particles
      • electromagnetic radiation:
        • propagating disturbance of electric and magnetic fields (classical physics)
        • motion of photons (modern physics)
• Work-energy theorem
  • Work is done when the energy of an object changes form (energy transduction).
  • Work is done when energy is transfered from one object to another (energy transfer).
  • Work is done when energy changes.

  abbreviated version

  W = ∆E

  algebra version

  F∆s cos θ = ∆E

  calculus version

  ⌠ ⌡ F ⋅ ds = ∆E

• Units
  • The SI unit of work and energy is the joule, named after the English physicist and brewer James Joule (1818–1889).

    [J = N m = kg m²/s²]

  • The electronvolt is an acceptable non SI unit of energy. It is used for some applications in electromagnetism; solid state, atomic, nuclear, and particle physics; and related sciences like biophysics, chemistry, and astronomy. An electron volt is the work done a particle with one elementary charge when it is moved between two points with a potential difference of one volt. It is described in more detail in the section on electric potential (a.k.a. voltage).

    1 eV = (1.6 × 10⁻¹⁶ C)(1 V) = 1.6 × 10⁻¹⁶ J