drift(redirected from mesial drift)
Also found in: Dictionary, Thesaurus, Medical, Legal.
drift,deposit of mixed clay, gravel, sand, and boulders transported and laid down by glaciers. Stratified, or glaciofluvial, drift is carried by waters flowing from the melting ice of a glacier. The flowing water sorts the particles, generally depositing layers of coarser particles nearer the point of origin. Till, or boulder clay, which makes up the greater part of the drift, is unstratified, consisting of disorganized heaps of rocks that range widely in size. Till is deposited directly by the glacier itself without water transport. The drift may take the form of a drumlindrumlin
, smooth oval hill of glacial drift, elongated in the direction of the movement of the ice that deposited it. Drumlins, which may be more than 150 ft (45 m) high and more than 1-2 mi (.8 km) long, are common in New York, Wisconsin, Canada, and Northern Ireland.
..... Click the link for more information. , a kamekame
, low, steep, rounded hill or ridge of layered sand and gravel drift, developed from glacial deposits. Kames were probably formed by streams of melting glacial ice that deposited mud and sand along the ice front.
..... Click the link for more information. , an eskeresker,
long, narrow, winding ridge of stratified sand-and-gravel drift. Eskers, many miles long and resembling abandoned railway embankments, occur in Scandinavia, Ireland, Scotland, and New England; they arose from deposition of sediment in the beds of streams flowing through
..... Click the link for more information. , a morainemoraine
, a formation composed of unsorted and unbedded rock and soil debris called till, which was deposited by a glacier. The till that falls on the sides of a valley glacier from the bounding cliffs makes up lateral moraines, running parallel to the valley sides.
..... Click the link for more information. , or an outwash plain; its thickness varies noticeably from place to place and is not dependent upon topographical factors. Presence of drift proved useful in establishing the existence of time periods when large parts of the surface of continents were covered with glaciers (see glacial periodsglacial periods,
times during which large portions of the earth's surface were covered with thick glacial ice sheets. In the Pleistocene epoch, in the Carboniferous and Permian periods of the Paleozoic era era, and in Huronian time of the Precambrian, the earth experienced an
..... Click the link for more information. ). Large sections of continental Europe and North America are covered by drift.
the lateral deviation from the plane of fire of a rotating artillery shell (bullet) during its flight through the air.
Drift is explained by the gyroscopic property possessed by the rotating shell. When the shell is moving in a straight line, the axis of its own rotation coincides with the direction of movement. Influenced by the force of gravity, the projectile’s trajectory curves, the tangent of the trajectory (which coincides with the direction of movement) grows continually lower, and the axis of the shell’s own rotation tries to maintain its own position in space, forming an angle with the tangent to the trajectory. The force of air resistance begins to act at an angle to the axis of the shell, which leads to the appearance of a moment that overturns the shell and of a component of the force of air resistance that is perpendicular to the axis of the shell. Influenced by the overturning moment, the shell makes a precessional movement, during which the axis of the shell’s rotation moves around the tangent to the trajectory, describing a cone whose apex is the center of the mass of the shell.
When the tangent is steadily dropping, this movement occurs asymmetrically relative to the direction of movement. Depending on the direction of the shell’s own rotation (right or left rifling in the bore of the gun), its nose will normally be more to the right than the left (or the opposite), that is, the precessional movement of the shell occurs around an axis deflected from the direction of movement to the right (or to the left), which is called the axis of dynamic equilibrium. As a result of this a perpendicular force arises that carries the shell’s center of mass to the right (or left) of the plane of fire; that is, it causes drift. The magnitude of drift depends on the curve of the trajectory and the rate of the shell’s precession; the smaller the curve of the trajectory, the smaller the drift will be. This explains why drift is insignificant with flat trajectories and short firing ranges and why it is not present when firing vertically upward.
Drift is taken into account by making corrections when firing; in some cases, compensation occurs automatically, having been done when the sighting devices were set. The phenomenon of drift was studied in 1865-70 and first explained by the Russian scientist N. V. Maievskii.
IU. V. CHUEV and K. A. NIKOLAEV
with regard to ships, the displacement of a moving ship from the line of its set course under the influence of wind and waves. Drift is characterized by its angle, that is, the angle between the longitudinal axis of the ship and the direction of its actual motion. Drift is included in the calculation of the ship’s course. To “lie in drift” means to hold the ship in place, compensating for the action of the wind and the waves by the engine, the sails, the floating anchor, or other means. The term “drift” also means the movement of a ship if the engine does not work and the ship is moving under the influence of the wind or the current, for instance, if the anchor is “creeping” along the bottom.
ii. A slow movement in one direction of an instrument pointer or other marker.
iii. A slow change in frequency of a radio transmitter.
iv. The angular deviation of the spin axis of a gyro from a fixed reference in space.
v. The angular deviation of a heading indicator of a gyrocompass resulting from either real or apparent precession. See apparent drift.
vi. The movement of a parachutist downwind.
vii. In ballistics, a shift in projectile direction caused by a gyroscopic action that results from gravitational and atmospherically induced torque or the earth's rotation.
viii. The failure of photograph(s) to stay on the predetermined flight line. If the drifting is excessive, repeated flights will have to be made because of serious gaps between adjacent flight lines.