The gal (symbol: Gal), sometimes called galileo after

Galileo Galilei Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...

, is a unit of

acceleration In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by the ...

sometimes used in

gravimetry Gravimetry is the measurement of the strength of a gravitational field. Gravimetry may be used when either the magnitude of a gravitational field or the properties of matter responsible for its creation are of interest. Units of measurement G ...

. BIPM ''SI brochure'', 8th ed. 2006
Table 9: Non-SI units associated with the CGS and the CGS-Gaussian system of units
. 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

International System of Units The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. E ...

(known by its French-language initials "SI"). In 1978 the

CIPM The General Conference on Weights and Measures (GCWM; french: Conférence générale des poids et mesures, CGPM) is the supreme authority of the International Bureau of Weights and Measures (BIPM), the intergovernmental organization established i ...

decided that it was permissible to use the gal "with the SI until the CIPM considers that tsuse is no longer necessary". However, use of the gal is deprecated by ISO 80000-3:2006. The gal is a derived unit, defined in terms of the centimeter–gram–second (CGS) base unit of length, the

centimeter 330px, Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its deriveds scales. The Microwave are in-between 1 meter to 1 millimeter. A centimetre (international spelling) or centimeter (American spellin ...

, and the

second The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ...

, 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 In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

and

elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § Vert ...

. Mountains and masses of lesser density within the Earth's crust typically cause variations in

gravitational acceleration In physics, gravitational acceleration is the acceleration of an object in free fall within a vacuum (and thus without experiencing drag). This is the steady gain in speed caused exclusively by the force of gravitational attraction. All bodi ...

of tens to hundreds of milligals (mGal). The gravity

gradient In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gr ...

(variation with height) above Earth's surface is about 3.1 µGal per centimeter of height (), resulting in a maximal difference of about 2 Gal (0.02 m/s²) from the top of

Mount Everest Mount Everest (; Tibetan: ''Chomolungma'' ; ) is Earth's highest mountain above sea level, located in the Mahalangur Himal sub-range of the Himalayas. The China–Nepal border runs across its summit point. Its elevation (snow heig ...

to sea level.Gravity Measurements
. University of Calgary. Accessed Nov 21, 2009. 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 The torr (symbol: Torr) is a unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (). Thus one torr is exactly (≈ ). Historically, one torr was intended to be the same as one " millimeter of merc ...

and its symbol, the unit name (gal) and its symbol (Gal) are spelled identically except that the latter is capitalized.

Conversions

References

{{DEFAULTSORT:Gal (Unit) Units of acceleration Centimetre–gram–second system of units Gravimetry

Conversions

See also

References