In biology and physics, animal locomotion is the study of how animals move, and is part of biophysics.

Much of the study is an application of Newton's third law of motion: if at rest, to move forwards an animal must push something backwards. Terrestrial animals must push the solid ground, swimming and flying animals must push against a fluid (either air or water). The topic splits into the following disjoint categories:

1. animal locomotion on land (walking and running)
2. animal locomotion in air (bird flight)
3. animal locomotion in water (swimming including fish and ducks)
4. animal locomotion on the surface layer (small animals relying on surface tension such as the water strider)
5. animal locomotion by water-walkers (the Common Basilisk).
6. animal locomotion through the ground ('swimming' in sand or mud)
7. animal locomotion on the sea floor
8. animal locomotion on steep, vertical, and overhanging surfaces (climbing on trees or on rockfaces - for example, lemurs in trees, mountain goats on a cliff face, or flies or geckos on the ceiling)

The distinction between the second and third topics is that in the third, the animal does not need to expend energy to defeat gravity; in or on the water, buoyancy counteracts the animal's weight. Locomotion

See http://www.dukenews.duke.edu/2005/12/locomotiontheory.html

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