CG or CB
02-06-2008, 03:27 AM
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CG or CB
What is the difference between center of gravity and center of balance. From my understanding, balance is exactly what it sounds like, balance. Balance pencil on your finger.
Center of gravity (in my understanding) is the center mass of an object.
On an Airboat, the CB would be the point where the hull would balance if placed on a dowel.
The CG would be an imaginary point somewhere above the hull, ahead of the engine that would allow the equal distribution of weight at all angles. IE. upside down, sideways, at a 45 Deg.....
Am I even close on this one?
Physics confuses me.[&:]
Center of gravity (in my understanding) is the center mass of an object.
On an Airboat, the CB would be the point where the hull would balance if placed on a dowel.
The CG would be an imaginary point somewhere above the hull, ahead of the engine that would allow the equal distribution of weight at all angles. IE. upside down, sideways, at a 45 Deg.....
Am I even close on this one?
Physics confuses me.[&:]
02-06-2008, 09:30 AM
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RE: CG or CB
The two terms, used very loosely, can be sort of interchangeable with models. Depending on how 'picky' you are, they can, but do not actually mean, or have to mean, the same thing.
The center of balance deals with forces applied to the object/model, and the reaction of that object/model. The center of gravity (center of mass) deals with the point where the mass of the object 'seems' to be concentrated, typically determined by it's shape, what things 'weigh' and where they are placed/positioned. A sort of 'up-n-down' thingy.
The center of mass is a single point. The center of balance, to be useful, must be a volume of 'points' large enough that the typical reaction to applied forces is sort of broader or at least predictable. A 'usable range' of balance. Once that center of balance moves outside it's "box", or usable range, the object/model becomes unstable or unpredictable. It's center of mass hasn't changed.
Okay, so what does all that mean? It means, for instance, that any consumable fuel ought'a be placed at the center of balance so that it doesn't affect the reactions of the object/model as it's being consumed. If the fuel tank is placed outside of the usable range of the balance 'box', (in the nose of the boat), then the nose of the boat is going to get higher the longer the boat runs. See where that's going? The center of balance is a fore/aft and side/side sort of thingy.
The center of mass or the center of gravity as it's most usually expressed, should be 'low' in relation to the keel of a boat. The lower the better in most cases, depending on the shape and purpose of the boat. If the center of mass/gravity is too high, then any applied force can make the thing 'fall over', or turn up side down. That's the only reason that long, sticky-downy-thingy is on sailboats, to lower the center of mass/gravity to make it more stable because of where and how the motive force is applied to it's sail.
This is NOT a very 'scientific' way of describing this stuff, so isn't 'exact' by any means. But I'll bet you get the idea.
- 'Doc
The center of balance deals with forces applied to the object/model, and the reaction of that object/model. The center of gravity (center of mass) deals with the point where the mass of the object 'seems' to be concentrated, typically determined by it's shape, what things 'weigh' and where they are placed/positioned. A sort of 'up-n-down' thingy.
The center of mass is a single point. The center of balance, to be useful, must be a volume of 'points' large enough that the typical reaction to applied forces is sort of broader or at least predictable. A 'usable range' of balance. Once that center of balance moves outside it's "box", or usable range, the object/model becomes unstable or unpredictable. It's center of mass hasn't changed.
Okay, so what does all that mean? It means, for instance, that any consumable fuel ought'a be placed at the center of balance so that it doesn't affect the reactions of the object/model as it's being consumed. If the fuel tank is placed outside of the usable range of the balance 'box', (in the nose of the boat), then the nose of the boat is going to get higher the longer the boat runs. See where that's going? The center of balance is a fore/aft and side/side sort of thingy.
The center of mass or the center of gravity as it's most usually expressed, should be 'low' in relation to the keel of a boat. The lower the better in most cases, depending on the shape and purpose of the boat. If the center of mass/gravity is too high, then any applied force can make the thing 'fall over', or turn up side down. That's the only reason that long, sticky-downy-thingy is on sailboats, to lower the center of mass/gravity to make it more stable because of where and how the motive force is applied to it's sail.
This is NOT a very 'scientific' way of describing this stuff, so isn't 'exact' by any means. But I'll bet you get the idea.
- 'Doc
