The gal, sometimes called galileo, (symbol Gal) is a non-SI unit of acceleration used extensively in the science of gravimetry.[1][2] The gal is defined as 1 centimeter per second squared (1 cm/s²). In SI base units, 1 Gal is 0.01 m/s². It 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. Unless it is being used at the beginning of a sentence or in paragraph or section titles, the unit name gal and galileo are 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 gal and its symbol are similar to the all-lowercase abbreviation for gallon (gal). 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. The gravity gradient (variation with height) above Earth’s surface is about 3.1 µGal/cm. Mountains and masses of lesser density within the Earth's crust typically cause variations in gravitational acceleration of tens to hundreds of milligals (mGal). This variation is especially important in the field of geophysics. The gal is named after Galileo Galilei, a physicist who made the first measurements of the Earth’s gravity.
References
- ^ Barry N. Taylor, Guide for the Use of the International System of Units (SI), 1995, NIST Special Publication 811, Appendix B.
- ^ BIPM SI brochure, 8th ed. 2006, Table 9: Non-SI units associated with the CGS and the CGS-Gaussian system of units.
