center of gravity

n., pl., centers of gravity.

1. (Abbr. CG) The point in or near a body at which the gravitational potential energy of the body is equal to that of a single particle of the same mass located at that point and through which the resultant of the gravitational forces on the component particles of the body acts.
2. The point of greatest importance, interest, or activity: "The center of gravity for the English language is no longer Britain. American English is the greatest influence on English everywhere" (Robert W. Burchfield).

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The point from which the gravitational attraction of a body appears to act. In a uniform gravitational field this is coincident with the body's center of mass.

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A fixed point in a material body through which the resultant force of gravitational attraction acts. The resultant of all forces or attractions produced by the Earth's gravity on a body constitutes its weight. This weight is considered to be concentrated at the center of gravity in mechanical studies of a rigid body. The location of the center of gravity for a body remains fixed in relation to the body regardless of the orientation of the body. If supported at its center of gravity, a body would remain balanced in its initial position. See also Gravity; Resultant of forces.

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The point at which the whole weight of an object can be considered to act and, therefore, at which all parts of an object are in balance. The position of the centre of gravity varies according to the shape of the object. In objects with a regular shape, the centre of gravity coincides with its geometric centre. In objects with an irregular and variable shape (as in the human body), the centre of gravity cannot be defined easily and changes with every change in position of the body; it may not even lie within the physical substance of the body. The centre of gravity of a projectile in flight follows a fixed path, but body movements may raise or lower the body parts around the centre of gravity. In this way, it is possible to jump different heights even though the centre of gravity reaches the same height. See also sacral promontory.

Centre of gravity

Keeping weights low contributes to stability
For purposes of discussion and calculation, all the weights in a boat are imagined to be a single force acting vertically downward through the center of gravity (CG).The CG is important because it interacts with the center of buoyancy (CB) to make a boat stable. When a boat heels, the underwater hull shape changes and the CB moves out toward one side or another, thereby creating a righting moment that tends to bring the boat back to an upright position.The CG does not shift position as the boat heels, except when crew members in racing boats line the rail, or water ballast is pumped from tank to tank, or a canting keel is shifted to a new position.To a large extent, a boat’s stability depends on the location of the CG relative to waterline level. The lower the CG, the greater the righting moment. That’s why all heavy weights in boats, such as ballast, engines, and tanks of fluid, are kept as low as possible. Spare anchors, chain, batteries, stores, and even books will improve a boat’s stability if they are stowed low. However, outboard motors stowed on the aft pulpit, dinghies on deck, and jib poles

Naval architects use the term “center of gravity” (“G” in the diagrams) to mean the sum of all weights in a boat, acting vertically downward in a single force. This diagram shows a boat on an even keel and at an angle of starboard heel. The center of gravity (G) does not move as the boat heels to 10 degrees, but the center of buoyancy (B) shifts to starboard (B2). If we were to draw a vertical line straight up from B2, it would intersect another line drawn up from the hull’s centerline (like a mast) at a point called the metacenter (M). The amount of force available to return the boat to an even keel (the righting moment) is determined by the boat’s weight and by the distance from G to Z, which is a point above B2 and level with G. Through the first few degrees of heel, M (an indicator of initial stability) falls in about the same place as B moves outboard. But as the boat heels beyond about 10 degrees, M ceases to be an indicator of stability since it no longer focuses about a single point above center-line. In other words, M1 migrates substantially from its consistent low-heel-angle position (M).

stowed up the mast all detract from a boat’s stability.See also Center of Buoyancy.

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(DOD) Those characteristics, capabilities, or sources of power from which a military force derives its freedom of action, physical strength, or will to fight. Also called COGs. See also capability; decisive point.

The point in any solid where a single applied force could support it; the point where the mass of the object is equally balanced. The center of gravity is also called the center of mass. When a man on a ladder leans sideways so far that his center of gravity is no longer over his feet, he begins to fall.

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