# Foe (unit)

A foe is a unit of energy equal to 1044 joules or 1051 ergs, used to express the large amount of energy released by a supernova.[1] The word is an acronym derived from a part of the pronunciation "ten to the power of fifty-one ergs".[2]

It was coined by Gerald E. Brown of Stony Brook University in his work with Hans Bethe, because "it came up often enough in our work".[3] A bethe (B) is equivalent to a foe.[4] The bethe is named after Hans Bethe. It was coined by Steven Weinberg.[4]

This unit of measure is convenient because a supernova typically releases about one foe of observable energy in a very short period (which can be measured in seconds). In comparison, if the Sun had its current luminosity throughout its entire lifetime, it would release 3.827×1026 W × 3.1536×107 s/yr × 1010 yr ≈ 1.2 foe. One solar mass has a rest mass energy of 1787 foe.

## References

1. ^ Hartmann DH (April 1999). "Afterglows from the largest explosions in the universe". Proc. Natl. Acad. Sci. U.S.A. 96 (9): 4752–5. Bibcode:1999PNAS...96.4752H. doi:10.1073/pnas.96.9.4752. PMC 33568. PMID 10220364.
2. ^ Marc Herant; Stirling A. Colgate; Willy Benz; Chris Fryer (October 25, 1997). "Neutrinos and Supernovae" (PDF). Los Alamos Sciences. Los Alamos National Laboratory. Retrieved 2008-04-23.
3. ^ Gerald Brown (2006). Hans Bethe and His Physics. World Scientific. ISBN 981-256-609-0.
4. ^ a b Stephen Weinberg (2006). "A Bethe unit". Physics World. 19 (2). doi:10.1088/2058-7058/19/2/31.
Erg

The erg is a unit of energy and work equal to 10−7 joules. It originated in the centimetre–gram–second (CGS) system of units. It has the symbol erg. The erg is not an SI unit. Its name is derived from ergon (ἔργον), a Greek word meaning work or task.An erg is the amount of work done by a force of one dyne exerted for a distance of one centimeter. In the CGS base units, it is equal to one gram centimeter-squared per second-squared (g⋅cm2/s2). It is thus equal to 10−7 joules or 100 nanojoules (nJ) in SI units. An erg is approximately the amount of work done (or energy consumed) by one common house fly performing one "push up", the leg-bending dip that brings its mouth to the surface on which it stands and back up.

1 erg = 10−7 J = 100 nJ

1 erg = 10−10sn⋅m = 100 psn⋅m = 100 picosthène-metres

1 erg = 624.15 GeV = 6.2415×1011 eV

1 erg = 1 dyn⋅cm = 1 g⋅cm2/s2

Index of physics articles (F)

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Lego Exo-Force

LEGO Exo-Force is a LEGO toy line.

Units of energy

Because energy is defined via work, the SI unit for energy is the same as the unit of work – the joule (J), named in honor of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton metre and, in terms of SI base units

${\displaystyle 1\ \mathrm {J} =1\ \mathrm {kg} \left({\frac {\mathrm {m} }{\mathrm {s} }}\right)^{2}=1\ {\frac {\mathrm {kg} \cdot \mathrm {m} ^{2}}{\mathrm {s} ^{2}}}}$

An energy unit that is used in atomic physics, particle physics and high energy physics is the electronvolt (eV). One eV is equivalent to 1.60217653×10−19 J.

In spectroscopy the unit cm−1 = 0.000123986 eV is used to represent energy since energy is inversely proportional to wavelength from the equation ${\displaystyle E=h\nu =hc/\lambda }$.

In discussions of energy production and consumption, the units barrel of oil equivalent and ton of oil equivalent are often used. Cubic mile of oil is sometimes used as a unit of energy in discussions of global scale energy economics.

When discussing amounts of energy released in explosions or bolide impact events, the TNT equivalent unit is often used. The joule is the most used unit of energy.

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