stability

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equilibrium

equilibrium, state of balance. When a body or a system is in equilibrium, there is no net tendency to change. In mechanics, equilibrium has to do with the forces acting on a body. When no force is acting to make a body move in a line, the body is in translational equilibrium; when no force is acting to make the body turn, the body is in rotational equilibrium. A body in equilibrium at rest is said to be in static equilibrium. However, a state of equilibrium does not mean that no forces act on the body, but only that the forces are balanced. For example, when a lever is being used to hold up a raised object, forces are being exerted downward on each end of the lever and upward on its fulcrum, but the upward and downward forces balance to maintain translational equilibrium, and the clockwise and counterclockwise moments of the forces on either end balance to maintain rotational equilibrium. The stability of a body is a measure of its ability to return to a position of equilibrium after being disturbed. It depends on the shape of the body and the location of its center of gravity (see center of mass). A body with a large flat base and a low center of gravity will be very stable, returning quickly to its position of equilibrium after being tipped. However, a body with a small base and high center of gravity will tend to topple if tipped and is thus less stable than the first body. A body balanced precariously on a point is in unstable equilibrium. Some bodies, such as a ball or a cone lying on its side, do not return to their original position of equilibrium when pushed, assuming instead a new position of equilibrium; these are said to be in neutral equilibrium. In thermodynamics, two bodies placed in contact with each other are said to be in thermal equilibrium when, after a sufficient length of time, their temperatures are equal. Chemical equilibrium refers to reversible chemical reactions in which the reactions involved are occurring in opposite directions at equal rates, so that no net change is observed.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Stability

 

of a vessel, the ability of a vessel to withstand the external forces that cause it to roll or pitch and to return to the original equilibrium position after these forces have ceased to operate. Stability is one of the most important seakeeping qualities of a vessel. Resistance to rolling is called transverse stability, and resistance to pitching is called longitudinal stability. Because of the elongated shape of a vessel, its longitudinal stability is significantly greater than its transverse stability. Hence assurance of proper transverse stability for safety at sea is a more important design consideration.

A distinction is made between static stability and dynamic stability. Static stability is measured in terms of the righting moment that is developed when a vessel is tilted to a certain angle of heel or trim, and the dynamic stability is measured in terms of the work of this moment. For small angles of heel the righting moment is approximately proportional to the angle of heel, the displacement, and the metacentric height.

Under operating conditions, the transverse stability is checked by determining the metacentric height and comparing it with the value that is safe for the particular vessel. Standards for transverse stability are set by the classification societies.

L. N. STRELIAEV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

stability

[stə′bil·əd·ē]
(chemistry)
The property of a chemical compound which is not readily decomposed and does not react with other compounds.
(control systems)
The property of a system for which any bounded input signal results in a bounded output signal.
(engineering)
The property of a body, as an aircraft, rocket, or ship, to maintain its attitude or to resist displacement, and, if displaced, to develop forces and moments tending to restore the original condition.
(fluid mechanics)
The resistance to overturning or mixing in the water column, resulting from the presence of a positive (increasing downward) density gradient.
(geology)
The resistance of a structure, spoil heap, or clay bank to sliding, overturning, or collapsing.
Chemical durability, resistance to weathering.
(materials)
Of a fuel, the capability to retain its characteristics in an adverse environment, for example, extreme temperature.
(mathematics)
Stability theory of systems of differential equations deals with those solution functions possessing some particular property that still maintain the property after a perturbation.
(mechanics)
(physics)
The property of a system which does not undergo any change without the application of an external agency.
The property of a system in which any departure from an equilibrium state gives rise to forces or influences which tend to return the system to equilibrium. Also known as static stability.
(plasma physics)
The property of a plasma which maintains its shape against externally applied forces (usually pressure of magnetic fields) and whose constituents can pass through confining fields only by diffusion of individual particles.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

stability

The resistance of a structure or element thereof to withstand sliding, overturning, buckling, or collapsing.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

stability

stabilityclick for a larger image
stabilityclick for a larger image
Atmospheric stability.
i. The ability of an aircraft to return to the same particular condition of flight after having been disturbed from that condition, without any effort on the part of the pilot. The illustration indicates how a stable aircraft returns to its level flight attitude once it is disturbed for any reason.
ii. A state of atmosphere in which the vertical distribution of temperature is such that a parcel of air will resist displacement from its initial level.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved

stability

1. the ability of an aircraft to resume its original flight path after inadvertent displacement
2. Meteorol
a. the condition of an air or water mass characterized by no upward movement
b. the degree of susceptibility of an air mass to disturbance by convection currents
3. Ecology the ability of an ecosystem to resist change
4. Electrical engineering the ability of an electrical circuit to cope with changes in the operational conditions
5. a vow taken by every Benedictine monk attaching him perpetually to the monastery where he is professed
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005