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"Lateral-directional" modes involve rolling motions and yawing motions. Motions in one of these axes almost always couples into the other so the modes are generally discussed as the "lateral-directional modes". [note 1] There are three types of possible lateral-directional dynamic motion: roll subsidence mode, spiral mode, and Dutch roll mode.
Lateral (from Latin lateralis 'to the side') describes something to the sides of an animal, as in "left lateral" and "right lateral". Medial (from Latin medius 'middle') describes structures close to the midline, [2] or closer to the midline than another structure. For example, in a human, the arms are lateral to the torso.
Medial and lateral, which describe a position that is closer to (medial) or farther from (lateral) the midline of the body. For example, the shoulders are lateral to the heart, and the umbilicus is medial to the hips. The medial side of the left knee is the side toward the opposite knee.
However, it is likely that this term, describing a lateral asymmetric motion of an airplane, was borrowed from a reference to similar-appearing motion in ice skating. In 1916, aeronautical engineer Jerome C. Hunsaker published: "Dutch roll – the third element in the [lateral] motion [of an airplane] is a yawing to the right and left, combined ...
Some of these terms come from Latin. Sagittal means "like an arrow", a reference to the position of the spine that naturally divides the body into right and left equal halves, the exact meaning of the term "midsagittal", or to the shape of the sagittal suture, which defines the sagittal plane and is shaped like an arrow.
The yaw rate is directly related to the lateral acceleration of the vehicle turning at constant speed around a constant radius, by the relationship tangential speed*yaw velocity = lateral acceleration = tangential speed^2/radius of turn, in appropriate units. The sign convention can be established by rigorous attention to coordinate systems.
Most of the principal terms can be combined using their corresponding combining forms (such as mesio-for mesial and disto-for distal). They provide names for directions (vectors) and axes; for example, the coronoapical axis is the long axis of a tooth. Such combining yields terms such as those in the following list.
These terms are used in descriptions of engineering, physics, and other sciences, as well as ordinary day-to-day discourse. Though these terms themselves may be somewhat ambiguous, they are usually used in a context in which their meaning is clear. For example, when referring to a drive shaft it is clear what is meant by axial or radial directions.