Animal locomotion, which is the act of self-propulsion by an animal, has many manifestations, including running, swimming, jumping and flying. Animals move for a variety of reasons, such as to find food, a mate, or a suitable microhabitat, and to escape predators. For many animals the ability to move is essential to survival and, as a result, selective pressures have shaped the locomotion methods and mechanisms employed by moving organisms. For example, migratory animals that travel vast distances (such as the Arctic Tern) typically have a locomotion mechanism that costs very little energy per unit distance, whereas non-migratory animals that must frequently move quickly to escape predators (such as frogs) are likely to have costly but very fast locomotion. The study of animal locomotion is typically considered to be a sub-field of biomechanics.
Locomotion requires energy to overcome friction, drag, inertia, and gravity, though in many circumstances some of these factors are negligible. In terrestrial environments gravity must be overcome, though the drag of air is much less of an issue. In aqueous environments however, friction (or drag) becomes the major challenge, with gravity being less of a concern. Although animals with natural buoyancy need not expend much energy maintaining vertical position, some will naturally sink and must expend energy to remain afloat. Drag may also present a problem in flight, and the aerodynamically efficient body shapes of birds highlight this point. Flight presents a different problem from movement in water however, as there is no way for a living organism to have lower density than air. Limbless organisms moving on land must often contend with surface friction, but do not usually need to expend significant energy to counteract gravity.
The Arabian or Arab horse (Arabic: الحصان العربي [ ħisˤaːn ʕarabiː], DMG ḥiṣān ʿarabī) is a breed of horse that originated on the Arabian Peninsula. With a distinctive head shape and high tail carriage, the Arabian is one of the most easily recognizable horse breeds in the world. It is also one of the oldest breeds, with archaeological evidence of horses that resemble modern Arabians dating back 4,500 years. Throughout history, Arabian horses spread around the world by both war and trade, used to improve other breeds by adding speed, refinement, endurance, and strong bone. Today, Arabian bloodlines are found in almost every modern breed of riding horse.
The Arabian developed in a desert climate and was prized by the nomadic Bedouin people, often being brought inside the family tent for shelter and protection from theft. Selective breeding for traits including an ability to form a cooperative relationship with humans created a horse breed that is good-natured, quick to learn, and willing to please. The Arabian also developed the high spirit and alertness needed in a horse used for raiding and war. This combination of willingness and sensitivity requires modern Arabian horse owners to handle their horses with competence and respect.
The Arabian is a versatile breed. Arabians dominate the discipline of endurance riding, and compete today in many other fields of equestrian activity. They are one of the top ten most popular horse breeds in the world. They are now found worldwide, including the United States and Canada, the United Kingdom, Australia, continental Europe, South America (especially Brazil), and its land of origin, the Middle East.