stability(redirected from Car stability)
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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.
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
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.