Summary
Buoyancy (also known as the buoyant force) is the force exerted on an object that is wholly or partly immersed in a fluid.
The symbol for the magnitude of buoyancy is B or FB
As a vector it must be stated with both magnitude and direction.
Buoyancy acts upward for the kind of situations encountered in everyday experience.
As with other forces, the SI unit of buoyancy is the newton [N].
Buoyancy is caused by differences in pressure acting on opposite sides of an object immersed in a static fluid.
A typical situation:The pressure on the bottom of an object is greater than the top
(since pressure increases with depth).
The force on the bottom pushes up and the force on the top pushes down
(since force is normal to the surface).
The direction of the net force due to the fluid is upward.
Pressure variations in a fluid are typically caused by gravity (since P = P0 + ρgh), but in general buoyant forces act opposite the direction of the frame of reference acceleration.
Under conditions of apparent weightlessness there can be no buoyant forces.
Archimedes' Principle
The magnitude of the buoyant force on an object is equal to the weight of the fluid it displaces.
B = ρgVdisplaced
The factors that affect buoyancy are …
the density of the fluid,
the volume of the fluid displaced, and
the local acceleration due to gravity.
The buoyant force is not affected by …
the mass of the immersed object or
the density of the immersed object.
A fluid is a substance that flows easily. Gases and liquids are fluids, although sometimes the dividing line between liquids and solids is not always clear. Because of their ability to flow, fluids can exert buoyant forces, multiply forces in a hydraulic systems, allow aircraft to fly and ships to float.
The topic that this page will explore will be pressure and depth. If a fluid is within a container then the depth of an object placed in that fluid can be measured. The deeper the object is placed in the fluid, the more pressure it experiences. This is because is the weight of the fluid above it. The more dense the fluid above it, the more pressure is exerted on the object that is submerged, due to the weight of the fluid.
The formula that gives the P pressure on an object submerged in a fluid is:
P = r * g * h
where
r (rho) is the density of the fluid,
g is the acceleration of gravity
h is the height of the fluid above the object
If the container is open to the atmosphere above, the added pressure must be included if one is to find the total pressure on an object. The total pressure is the same as absolute pressure on pressure gauges readings, while the gauge pressure is the same as the fluid pressure alone, not including atmospheric pressure.
Ptotal = Patmosphere + Pfluid
Ptotal = Patmosphere + ( r * g * h )
A Pascal is the unit of pressure in the metric system. It represents 1 newton/m2
