Acceleration due to gravity: Difference between revisions
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''M''<sub>E</sub> is the total mass of the Earth, and ''R''<sub>E</sub> is the radius of the Earth. This equation gives a good approximation, but is not exact. Deviations are caused by the [[centrifugal force]] due to the rotation of the Earth around its axis, non-sphericity of the Earth, and the non-homogeneity of the composition of the Earth. These effects cause ''g'' to vary roughly ± 0.01 around the value 9.8 m s<sup>−2</sup> from place to place on the surface of the Earth. The quantity ''g'' is therefore referred to as the ''local gravitational acceleration''. | ''M''<sub>E</sub> is the total mass of the Earth, and ''R''<sub>E</sub> is the radius of the Earth. This equation gives a good approximation, but is not exact. Deviations are caused by the [[centrifugal force]] due to the rotation of the Earth around its axis, non-sphericity of the Earth, and the non-homogeneity of the composition of the Earth. These effects cause ''g'' to vary roughly ± 0.01 around the value 9.8 m s<sup>−2</sup> from place to place on the surface of the Earth. The quantity ''g'' is therefore referred to as the ''local gravitational acceleration''. | ||
The 3rd General Conference on Weights and Measures (Conférence Générale des Poids et Mesures, CGPM) defined in 1901 a standard value denoted as ''g<sub>n</sub>''.<ref>[http://physics.nist.gov/Document/sp330.pdf The International System of Units (SI), NIST Special Publication 330, 2001 Edition] (pdf page 29 of 77 pdf pages)</ref> | The 3rd [[General Conference on Weights and Measures]] (Conférence Générale des Poids et Mesures, CGPM) defined in 1901 a standard value denoted as ''g<sub>n</sub>''.<ref>[http://physics.nist.gov/Document/sp330.pdf The International System of Units (SI), NIST Special Publication 330, 2001 Edition] (pdf page 29 of 77 pdf pages)</ref> | ||
<ref>[http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf Bureau International des Poids et Mesures] (Brochure on SI, pdf page 51 of 88 pdf pages) From the website of the [[Bureau International des Poids et Mesures]]</ref> The value of the ''standard acceleration due to gravity'' ''g<sub>n</sub>'' is 9.80665 m s<sup>−2</sup>. This value of ''g<sub>n</sub>'' was the conventional reference for calculating the now obsolete unit of force, the kilogram force. | <ref>[http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf Bureau International des Poids et Mesures] (Brochure on SI, pdf page 51 of 88 pdf pages) From the website of the [[Bureau International des Poids et Mesures]]</ref> The value of the ''standard acceleration due to gravity'' ''g<sub>n</sub>'' is 9.80665 m s<sup>−2</sup>. This value of ''g<sub>n</sub>'' was the conventional reference for calculating the now obsolete unit of force, the kilogram force. | ||
==References== | ==References== | ||
<references/> | <references/> | ||
Revision as of 10:48, 16 April 2011
An object with mass m near the surface of the Earth experiences a downward gravitational force of magnitude mg, where g is the acceleration due to gravity. The quantity g has the dimension of acceleration, m s−2, hence its name.
Newton's gravitational law gives the following formula for g,
where G is the universal gravitational constant,[1] G = 6.67428 × 10−11 m3 kg−1 s−2, ME is the total mass of the Earth, and RE is the radius of the Earth. This equation gives a good approximation, but is not exact. Deviations are caused by the centrifugal force due to the rotation of the Earth around its axis, non-sphericity of the Earth, and the non-homogeneity of the composition of the Earth. These effects cause g to vary roughly ± 0.01 around the value 9.8 m s−2 from place to place on the surface of the Earth. The quantity g is therefore referred to as the local gravitational acceleration.
The 3rd General Conference on Weights and Measures (Conférence Générale des Poids et Mesures, CGPM) defined in 1901 a standard value denoted as gn.[2] [3] The value of the standard acceleration due to gravity gn is 9.80665 m s−2. This value of gn was the conventional reference for calculating the now obsolete unit of force, the kilogram force.
References
- ↑ Source: CODATA 2006, retrieved 2/24/08 from NIST website
- ↑ The International System of Units (SI), NIST Special Publication 330, 2001 Edition (pdf page 29 of 77 pdf pages)
- ↑ Bureau International des Poids et Mesures (Brochure on SI, pdf page 51 of 88 pdf pages) From the website of the Bureau International des Poids et Mesures