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Action and reaction pair for buoyant force.

by kennykwong
Tags: action, buoyant, force, pair, reaction
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kennykwong
#1
Jan9-13, 12:33 AM
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According to Newton 3rd law, every action will have a reaction. but how about buoyant force? if the buoyant force is the force of water on object then the reaction force will be the force of object on water. but is it other name for this force?
thanks for reply.
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haruspex
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Jan9-13, 12:41 AM
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Yes, there is an equal and opposite force from the object on the water. I'm not aware of any specific name for it.
Bear in mind that the buoyant force is the integral of the pressure over the surface (as a vector), and the reaction force is likewise.
SteamKing
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Jan9-13, 03:20 AM
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The buoyant force for a floating body is produced in reaction to the weight of the body.
By Archimedes Principle, the weight of a floating body is equal to the weight of fluid displaced by the body.

kennykwong
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Jan9-13, 05:09 AM
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Action and reaction pair for buoyant force.

Quote Quote by SteamKing View Post
The buoyant force for a floating body is produced in reaction to the weight of the body.
By Archimedes Principle, the weight of a floating body is equal to the weight of fluid displaced by the body.
this is what i thought at first but when comes to action and reaction force pair, should it be somethings like force of water on object and object on water. furthermore, the weight is the force which act from gravity to the object not from water right? i think weight and buoyant force are the forces acting ON the OBJECT but not a force pair.
please correct me if i am wrong
haruspex
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Jan9-13, 02:09 PM
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Quote Quote by SteamKing View Post
The buoyant force for a floating body is produced in reaction to the weight of the body.
By Archimedes Principle, the weight of a floating body is equal to the weight of fluid displaced by the body.
For a floating body at equilibrium (not being accelerated) the two forces will be equal, but I wouldn't say the buoyant force is in reaction to the weight of the body. It is just the integral of the pressure over the surface of the body, and this is true whether the body is sinking, bobbing up and down, resting on the ocean floor... The equal reaction from the body is in the same manner, distributed over its surface.


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