Is buoyancy a force
1. Definition formula: F floating = f lower - f upper
The formula of Archimedes principle: F floating = g row= ρ GV row The formula holds only when the object is suspended or floating on the surface of liquid. ρ Things & lt; ρ When the object is floating, when the object is floating, ρ Things= ρ Liquid Force analysis: F float = g matter - f pull, the object is in equilibrium under buoyancy, gravity and downward pressure, then the buoyancy formula is: F float = g matter + f pressure 
extended data:
the cause of buoyancy can be analyzed by a cube immersed in liquid. It is a fully immersed body, which is subjected to the pressure of liquid in all directions and increases with the increase of depth
the front and back, left and right, upper and lower sides of the cube are all under the pressure of liquid. Because the forces acting on the left and right sides correspond to each other and have the same area
is at the same depth in the liquid, so the pressure on the two sides is equal, the direction is opposite, and the two forces are balanced with each other. In the same way, the pressure acting on the front and rear sides is balanced with each other
for the whole composed of body and liquid, it is internal force.
because buoyancy is the upward pressure of liquid on the object immersed in it
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F floating = f upward-f downward
"f upward" refers to the upward force on the lower surface, and f downward refers to the downward force on the upper surface, which is the most original calculation formula of buoyancy
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F floating = g row = ρ Liquid GV row
this is based on Archimedes' principle. V row refers to the volume of liquid discharged, ρ Liquid refers to the density of liquid
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F floating = g object
i.e ρ Liquid GV discharge = ρ Object GV object, the use of two force balance, that is, according to the floating, floating objects buoyancy and self weight equal
When measuring buoyancy, according to this formula, f-pull refers to the tension of the spring dynamometer -
F= ρ GH
H refers to the height of the surface from the liquid level when the object is completely immersed in the liquid
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extended data
force refers to the difference (resultant force) of fluid (liquid and gas) pressure on each surface of an object in fluid (including liquid and gas). In 245 BC, Archimedes discovered the principle of buoyancy
The definition formula of buoyancy is f floating = g row (that is, the buoyancy of an object is equal to the gravity of the liquid discharged when the object sinks)= ρ Liquid GV discharge ρ Liquid: liquid density, kg / m3; g: The ratio of gravity to mass g = 9.8n/kg. In rough calculation, G can be taken as 10N / kg, in Newton; V row: volume of liquid discharged, unit: cubic meter). The buoyancy of liquids also applies to gases The point of action ofbuoyancy is called the center of buoyancy. The center of buoyancy obviously coincides with the centroid of the volume of the discharged liquid
friction does not belong to elasticity
when we analyze the force on the object, we analyze the force of other objects on the object in the order of gravity, elasticity and friction
this is taught by the competition class teacher. I think it makes sense. The school teachers don't think so. I didn't discuss it with him either.
the first case: the object floats up in water: in this state, the weight of the object is less than the buoyancy of water. In this case, f floats & gt; G, ρ Things & lt; ρ Liquid.
the second case: the object is floating in the water: in this state, the weight of the object is equal to the buoyancy of the fluid. At this point, f = G, ρ Things & lt; ρ Liquid.
the third state: the object is suspended in water: in this state, the weight of the object is equal to the buoyancy of the fluid. At this point, f = G, ρ Things= ρ Liquid.
the fourth state: in this state, the weight of the object is greater than the buoyancy of the fluid. At this time f floats & lt; G, ρ Things & gt; ρ Liquid.
the fifth state: when the object is in close contact with the bottom of the fluid, the bottom of the object is not subject to any buoyancy.
the generation of buoyancy requires us to think about pressure
immerse a square in water. We all know that water will exert pressure on all sides of the square, and the deeper the water is, the greater the pressure is
moreover, the pressure generated by the water pressure must be the "squeezing force" perpendicular to the contact face inside the object (it can be vividly thought of as the force trying to squeeze the block into a point). Therefore, the lower surface of the block is naturally deeper than the upper surface of the block, so the upward pressure on the lower surface is a little larger than the downward pressure on the upper surface
the extra point is the buoyancy of water
in all fluids, the pressure in the depth is always higher, and the pressure under any object is definitely upward, so the upward pressure on any object in the fluid will be a little higher than the downward pressure
the same is true for objects in the air. That's what makes air buoyancy
therefore, I think you have found the answer. If there is no fluid in vacuum, what will "squeeze" things in vacuum and proce pressure difference?
net reaction? I don't know what force it is, so I don't know how to seek it
can you explain
in physics, there seems to be no net reaction
supplementary answer:
I have never studied structure, but I have studied structural mechanics.