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

Galileo Galilei Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642), commonly referred to as Galileo Galilei ( , , ) or mononymously as Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a poly ...

, is a unit of

acceleration In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...

typically used in precision

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. The study of gravity c ...

. 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, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official s ...

(known by its

French-language French ( or ) is a Romance language of the Indo-European family. Like all other Romance languages, it descended from the Vulgar Latin of the Roman Empire. French evolved from Northern Old Gallo-Romance, a descendant of the Latin spoken in ...

initials "SI"). In 1978 the

CIPM The General Conference on Weights and Measures (abbreviated CGPM from the ) is the supreme authority of the International Bureau of Weights and Measures (BIPM), the intergovernmental organization established in 1875 under the terms of the Metre ...

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 Use of the gal was deprecated by the standard ISO 80000-3:2006, now superseded.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

centimeter upright=1.35, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is in-between 1 meter to 1 millimeter. A centimetre (International spelling) or centimeter (American ...

, and the

second The second (symbol: s) is a unit of time derived from the division of the day first into 24 hours, then to 60 minutes, and finally to 60 seconds each (24 × 60 × 60 = 86400). The current and formal definition in the International System of U ...

, 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 at its surface is 976 to 983 Gal, the variation being due mainly to differences in

latitude In geography, latitude is a geographic coordinate system, geographic 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 t ...

and

elevation The elevation of a geographic location (geography), ''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 equipotenti ...

Standard gravity The standard acceleration of gravity or standard acceleration of free fall, often called simply standard gravity and denoted by or , is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. It is a constant ...

is 980.665 Gal. 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 (physics), drag). This is the steady gain in speed caused exclusively by 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 f of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p gives the direction and the rate of fastest increase. The g ...

(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 (), known locally as Sagarmatha in Nepal and Qomolangma in Tibet, is Earth's highest mountain above sea level. It lies in the Mahalangur Himal sub-range of the Himalayas and marks part of the China–Nepal border at it ...

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 Pressure#Units, unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (unit), atmosphere (101325 Pa). Thus one torr is exactly (≈ ). Historically, one torr was intended to be ...

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