Gal (unit)

Gal (unit)
Gravity anomalies covering the Southern Ocean are shown here in false-color relief. Amplitudes range between -30 mGal (magenta) to +30 mGal (red). This image has been normalized to remove variation due to differences in latitude

The gal, sometimes called galileo, (symbol Gal) is a unit of acceleration used extensively in the science of gravimetry.[1][2][3] The gal is defined as 1 centimeter per second squared (1 cm/s²).

The gal is not part of the International System of Units (known by its French-language initials “SI”). However, in 1978 the CIPM decided that it was permissible to use the gal “with the SI until the CIPM considers that [its] use is no longer necessary.”[2][4]

The gal is a derived unit, comprising the centimeter-gram-second (CGS) base unit of length, the centimeter, and the second, which is the base unit of time in both the CGS as well as the modern SI system. In SI base units, 1 Gal is precisely equal to 0.01 m/s².

The acceleration due to Earth’s gravity (see Standard gravity) at its surface is 976 to 983 Gal; the variation being due mainly to differences in latitude and elevation. Mountains and masses of lesser density within the Earth's crust typically cause variations in gravitational acceleration of tens to hundreds of milligals (mGal). The gravity gradient (variation with height) above Earth’s surface is about 3.1 µGal per centimeter of height (3.1×10−6 s–2), resulting in a maximum difference of about 2 Gal (0.02 m/s2) from the top of Mount Everest to sea level.[5]

Unless it is being used at the beginning of a sentence or in paragraph or section titles, the unit name gal is properly spelled with a lowercase g. As with the torr and its symbol, the unit name (gal) and its symbol (Gal) are spelled identically except that the latter is capitalized. The unit should not be confused with the identical all-lowercase abbreviation for gallon (gal).

The gal is named after Galileo Galilei, a physicist who made the first measurements of the Earth’s gravity.

It can also be used to measure peak ground acceleration in earthquakes.

See also

References

  1. ^ Barry N. Taylor, Guide for the Use of the International System of Units (SI), 1995, NIST Special Publication 811, Appendix B.
  2. ^ a b BIPM SI brochure, 8th ed. 2006, Table 9: Non-SI units associated with the CGS and the CGS-Gaussian system of units.
  3. ^ Some sources, such as the University of North Carolina, the European Space Agency, and ConversionTables.com state that the unit name is “galileo”. The NIST and the BIPM are here considered as more authoritative sources regarding the proper unit name.
  4. ^ NIST Guide to SI Units; Section 5, Units Outside the SI; Subsection 5.2: Units temporarily accepted for use with the SI.
  5. ^ Gravity Measurements. University of Calgary. http://www.geo.ucalgary.ca/~wu/Goph547/Gravimeters.pdf Accessed Nov 21, 2009.

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  • Gal — is usually a casual term for a woman. It can also refer to: * Gal Costa A Brazilian Bossa Nova singer. * Gal (unit), short for Galileo Unit: one centimeter per second squared * Gall Force, a 1980 s japanese anime. * Gallon * Galactose * Gal, a… …   Wikipedia

  • gal — gal1 [gal] n. Slang a girl or woman gal2 [gal] n. [< GAL(ILEO)] a unit of acceleration equal to one centimeter per second per second: used in gravimetry gal3 abbrev. gallon(s) …   English World dictionary

  • gal. — gal. (gallon) n. unit of liquid measure (equal to 3.78 liters) …   English contemporary dictionary

  • gal — unit of acceleration of one centimeter per second per second Rare Three Letter Words Units of Measurement …   Phrontistery dictionary

  • Gal (acceleration) — The gal, sometimes called galileo, (symbol Gal) is a unit of acceleration used extensively in the science of gravimetry. [Barry N. Taylor, Guide for the Use of the International System of Units (SI), 1995, NIST Special Publication 811,… …   Wikipedia

  • gal — gal1 /gal/, n. Informal. a girl or woman. [1785 95; orig. dial. pron. of GIRL] Usage. See girl. gal2 /gal/, n. a centimeter gram second unit of acceleration, equal to one centimeter per second per second. [1910 15; named after GALILEO] * * * ▪… …   Universalium

  • Gal. — abbr. Galatians (New Testament). * * * Galatians. * * * Gal. (Bible) abbrev (the Letter to the) Galatians * * * gal. abbreviation gallon Thesaurus: units for measuring amounts of liquidhyponym * * * gal1 « …   Useful english dictionary

  • gal. — abbr. Galatians (New Testament). * * * gallon; gallons. * * * Gal. (Bible) abbrev (the Letter to the) Galatians * * * gal. abbreviation gallon Thesaurus: units for measuring amounts of liquidhyponym * * * …   Useful english dictionary

  • gal — I. /gæl/ (say gal) noun Colloquial a girl. {British dialect variant of girl} II. /gæl/ (say gal) noun Colloquial galvanised iron. {abbreviation} III. /gæl/ (say gal …  

  • gal — I [[t]gæl[/t]] n. off use inf: sometimes off. a girl or woman • Etymology: 1785–95; by alter. of girl usage: See girl II gal [[t]gæl[/t]] n. wam a cgs unit of acceleration, equal to one centimeter per second per second • Etymology: 1910–15; after …   From formal English to slang

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