# Angular momentum

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**Angular momentum** is the product of mass times the perpendicular distance from the axis of rotation times the rotation velocity. The angular momentum about the Earth’s axis of rotation can be expressed as the sum of the angular momentum of the solid Earth’s rotation plus the angular momentum of zonal air motion relative to the surface of the Earth. Were this quantity to be absolutely conserved, a parcel of air with the angular momentum of the Earth’s surface at the Equator would have a westerly zonal wind speed of 134 m/s at 30^{o} latitude.

## Scale of definition

The concept of angular momentum is used in the practical world around us to quantify the spin momentum of figure skaters, merry-go-rounds and any other object in circular motion; the concept is also very useful in planetary and galactic level motions of celestial bodies, such as the moon's motion around the Earth. In addtion the notion of angular momentum is useful in analyzing the atomic. molecular and subatomic world, where elementary particles are the objects of interest. In those cases it is more difficult to realize an intuitive picture of many of the subatomic uses of angular momentum, due to the role of the Heisenberg Uncertainty principle.

## Further Reading

- Dennis L. Hartmann.
*Global Physical Climatology.*Academic Press, 1994.

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