Gal (unit)

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gal
CGS units
Unit ofAcceleration
SymbolGal
Named afterGalileo Galilei
Conversions
1 Gal in ...... is equal to ...
   CGS base units   1 cm/s2
   SI units   0.01 m/s2
   Imperial, US customary   0.03280840 ft/s2
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 (symbol: Gal), sometimes called galileo after Galileo Galilei, is a unit of acceleration typically used in precision gravimetry.[2][3][4] The gal is defined as 1 centimeter per second squared (1 cm/s2). The milligal (mGal) and microgal (µGal) are respectively one thousandth and one millionth of a gal.

The gal is not part of the

ISO 80000-3:2006
, now superseded.

The gal is a derived unit, defined in terms of the

centimeter, and the second
, which is the base unit of time in both the CGS and the modern SI system. In SI base units, 1 Gal is 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 maximal difference of about 2 Gal (0.02 m/s2) from the top of Mount Everest to sea level.[6]

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.

Conversions

Conversions between common units of acceleration
Base value (Gal, or cm/s2) (ft/s2) (m/s2) (Standard gravity, g0)
1 Gal, or cm/s2 1 0.0328084 0.01 1.01972×10−3
1 ft/s2 30.4800 1 0.304800 0.0310810
1 m/s2 100 3.28084 1 0.101972
1 g0 980.665 32.1740 9.80665 1

See also

References

  1. NASA Jet Propulsion Laboratory
    . Retrieved 30 December 2013.
  2. NIST Special Publication 811, Appendix B
    .
  3. ^ .
  4. ^ Some sources, such as the University of North Carolina Archived 2012-02-18 at the Wayback Machine, the European Space Agency, and ConversionTables.com Archived 2009-05-19 at the Wayback Machine state that the unit name is "galileo". The NIST and the BIPM are here considered as more authoritative sources regarding the proper unit name.
  5. ^ NIST Guide to SI Units; Section 5, Units Outside the SI; Subsection 5.2: Units temporarily accepted for use with the SI.
  6. ^ Gravity Measurements Archived 2009-03-06 at the Wayback Machine. University of Calgary. Accessed Nov 21, 2009.