Energy

Discussion

A system possesses energy if it has the ability to do work.

Work shifts energy from one system to another.

Energy is …

Energy can exist in many different forms. All forms of energy are either kinetic or potential. The energy associated with motion is called kinetic energy. The energy associated with position is called potential energy. Potential energy is not "stored energy". Energy can be stored in motion just as well as it can be stored in position. Is kinetic energy "used up energy"?

Another scheme (economic)

units

For those who want some proof that physicists are human, the proof is is the idiocy of all the different units which they use for measuring energy. — Richard Feynman.

Energy Units Discussed in This Book
unit joule equivalent other equivalent reference
joule 1 J     N m work
erg 0.1 μJ     dyne cm "
foot pound 1.35582 J (approximate)   "
watt second 1 J       power
watt hour 3.6 kJ     3600 W s "
kilowatt hour 3.6 MJ     1000 W h "
thermochemical calorie 4.184 J (by definition)   heat
International Table calorie 4.1868 J (by definition)   "
kilocalorie*       1000 calorie "
thermochemical Btu** 1.054350 kJ (approximate)   "
International Table Btu** 1.05505585262 kJ (by definition)   "
therm         100,000 Btu "
quad*** 1.055 EJ (approximate) 1015 Btu "
cubic meter natural gas 37–39 MJ (variable)   chemical
ton of oil equivalent 41–45 GJ (variable)   "
ton of coal equivalent 29.3 GJ (approximate)   "
ton of TNT 4.184 GJ (by definition)   "
* The kilocalorie is also known as the kilogram calorie, dietetic calorie, food calorie, and Calorie (with an uppercase "C").
** Btu is the abbreviation for "British thermal unit".
*** Quad is the shortened form of "quadrillion Btu".
Energy Equivalents from Atomic and Nuclear Physics
unit symbol joule equivalent
atomic mass unit u muc2 = 1.492 × 10−10 J
electron volt eV e = 1.602 × 10−19 J
hartree Eh 2Rhc = 4.35974381 × 10−18 J (exact)
inverse meter m−1 hc = 1.986 × 10−25 J
inverse second s−1 h = 6.626 × 10−34 J
kelvin K k = 1.381 × 10−23 J
kilogram kg c2 = 89,875,517,873,681,764 J (exact)
Where: c  =  speed of light in a vacuum k  =  Boltzmann constant
  e  =  elementary charge mu  =  atomic mass unit
  h  =  Planck constant R  =  Rydberg constant

Historical Notes

 

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