# Gal (unit)

The gal (symbol: Gal), sometimes called galileo after Galileo Galilei, is a unit of acceleration used extensively in the science of gravimetry.[2][3][4] The gal is defined as 1 centimeter per second squared (1 cm/s2). The milligal (mGal) and microgal (µGal) refer respectively to one thousandth and one millionth of a gal.

The gal is not part of the International System of Units (known by its French-language initials "SI"). 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".[3][5] 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, 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.

Earth's gravity measured by NASA GRACE mission, showing deviations from the theoretical gravity of an idealized smooth Earth, the so-called earth ellipsoid. Red shows the areas where gravity is stronger than the smooth, standard value, and blue reveals areas where gravity is weaker. (Animated version.)[1]
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.

## 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 0.00101972
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

## References

1. ^ NASA/JPL/University of Texas Center for Space Research. "PIA12146: GRACE Global Gravity Animation". Photojournal. NASA Jet Propulsion Laboratory. Retrieved 30 December 2013.
2. ^ Barry N. Taylor, Guide for the Use of the International System of Units (SI), 1995, NIST Special Publication 811, Appendix B.
3. ^ a b BIPM SI brochure, 8th ed. 2006, Table 9: Non-SI units associated with the CGS and the CGS-Gaussian system of units Archived 2007-10-18 at the Wayback Machine..
4. ^ Some sources, such as the University of North Carolina, 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.
Airbus Corporate Jets

Airbus Corporate Jets, a business unit of Airbus SAS and part of Airbus, markets and completes corporate jet variants from the parent's airliner range. Types include the A318 Elite to the double/triple-decked Airbus A380 Prestige. Following the entry of the 737 based Boeing Business Jet, Airbus joined the business jet market with the A319 Corporate Jet in 1997. Although the term Airbus Corporate jet was initially used only for the A319CJ, it is now often used for all models, including the VIP widebodies. As of December 2008, 121 corporate and private jets are operating, 164 aircraft have been ordered, including an A380 Prestige and 107 A320 family Corporate Jet.An Airbus Corporate Jet Centre is based at Toulouse, France and specialises in single-aisle aircraft.

Galileo Galilei

Galileo Galilei (Italian: [ɡaliˈlɛːo ɡaliˈlɛi]; 15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Galileo has been called the "father of observational astronomy", the "father of modern physics", the "father of the scientific method", and the "father of modern science".Galileo studied speed and velocity, gravity and free fall, the principle of relativity, inertia, projectile motion and also worked in applied science and technology, describing the properties of pendulums and "hydrostatic balances", inventing the thermoscope and various military compasses, and using the telescope for scientific observations of celestial objects. His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the observation of the four largest satellites of Jupiter, the observation of Saturn and the analysis of sunspots.

Galileo's championing of heliocentrism and Copernicanism was controversial during his lifetime, when most subscribed to either geocentrism or the Tychonic system. He met with opposition from astronomers, who doubted heliocentrism because of the absence of an observed stellar parallax. The matter was investigated by the Roman Inquisition in 1615, which concluded that heliocentrism was "foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture." Galileo later defended his views in Dialogue Concerning the Two Chief World Systems (1632), which appeared to attack Pope Urban VIII and thus alienated him and the Jesuits, who had both supported Galileo up until this point. He was tried by the Inquisition, found "vehemently suspect of heresy", and forced to recant. He spent the rest of his life under house arrest. While under house arrest, he wrote Two New Sciences, in which he summarized work he had done some forty years earlier on the two sciences now called kinematics and strength of materials.

Index of physics articles (G)

The index of physics articles is split into multiple pages due to its size.

Messerschmitt Me 262

The Messerschmitt Me 262, nicknamed Schwalbe (German: "Swallow") in fighter versions, or Sturmvogel (German: "Storm Bird") in fighter-bomber versions, was the world's first operational jet-powered fighter aircraft. Design work started before World War II began, but problems with engines, metallurgy and top-level interference kept the aircraft from operational status with the Luftwaffe until mid-1944. The Me 262 was faster and more heavily armed than any Allied fighter, including the British jet-powered Gloster Meteor. One of the most advanced aviation designs in operational use during World War II, the Me 262's roles included light bomber, reconnaissance and experimental night fighter versions.

Me 262 pilots claimed a total of 542 Allied aircraft shot down, although higher claims are sometimes made. The Allies countered its effectiveness in the air by attacking the aircraft on the ground and during takeoff and landing. Strategic materials shortages and design compromises on the Junkers Jumo 004 axial-flow turbojet engines led to reliability problems. Attacks by Allied forces on fuel supplies during the deteriorating late-war situation also reduced the effectiveness of the aircraft as a fighting force. Armament production within Germany was focused on more easily manufactured aircraft. In the end, the Me 262 had a negligible impact on the course of the war as a result of its late introduction and the consequently small numbers put in operational service.While German use of the aircraft ended with the close of World War II, a small number were operated by the Czechoslovak Air Force until 1951. Also it heavily influenced several designs, like Sukhoi Su-9 (1946) and Nakajima Kikka. Captured Me 262s were studied and flight tested by the major powers, and ultimately influenced the designs of post-war aircraft such as the North American F-86 Sabre, MiG-15 and Boeing B-47 Stratojet. Several aircraft survive on static display in museums, and there are several privately built flying reproductions that use modern General Electric J85 engines.

Non-SI units mentioned in the SI

This is a list of units that are not defined as part of the International System of Units (SI), but are otherwise mentioned in the SI, because either the General Conference on Weights and Measures (CGPM) accepts their use as being multiples or submultiples of SI-units, they have important contemporary application worldwide, or are otherwise commonly encountered worldwide.

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