Buoyancy Definition and 413 Threads

Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. The pressure difference results in a net upward force on the object. The magnitude of the force is proportional to the pressure difference, and (as explained by Archimedes' principle) is equivalent to the weight of the fluid that would otherwise occupy the submerged volume of the object, i.e. the displaced fluid.
For this reason, an object whose average density is greater than that of the fluid in which it is submerged tends to sink. If the object is less dense than the liquid, the force can keep the object afloat. This can occur only in a non-inertial reference frame, which either has a gravitational field or is accelerating due to a force other than gravity defining a "downward" direction.Buoyancy also applies to fluid mixtures, and is the most common driving force of convection currents. In these cases, the mathematical modelling is altered to apply to continuua, but the principles remain the same. Examples of buoyancy driven flows include the spontaneous separation of air and water or oil and water.
The center of buoyancy of an object is the center of gravity of the displaced volume of fluid.

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  1. L

    Archimedes Principle and Buoyancy

    Homework Statement A 100g object having a density less than that of water is placed into a beaker half full of water. The beaker is then placed on a triple beam balance. Would be measured weight be equal to, greater than, or less than the weights of the water, the beaker, and the object added...
  2. A

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  3. T

    Buoyancy, depth a block will sink in two different liquids

    Homework Statement 4. The bottom half of a tank is filled with water (ρ = 1.0 x 103 kg/m3), and the top half is filled with oil (ρ = 0.85 x 103 kg/m3). Suppose that a rectangular block of wood of mass 5.5 kg, 30 cm long, 20 cm wide and 10 cm high is placed in this tank. How deep will the...
  4. W

    How Does Depth Affect the Buoyant Force on a Submerged Beach Ball?

    A beach ball is made of thin plastic. It has been inflated with air, but the plastic is not stretched. By swimming with fins on, you manage to take the ball from the surface of a pool to the bottom. Once the ball is completely submerged, what happens to the buoyant force exerted on the beach...
  5. KiNGGeexD

    Buoyancy - block of concrete is being raised from a lake

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  6. C

    How Much of the Granite Rock Ball Must Be Submerged to Float?

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  7. P

    Effects of Temperature on a Balloon's Buoyancy?

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  8. J

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  9. gfd43tg

    What is the Weight of the Capsized Battleship Oklahoma at Pearl Harbor?

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  10. G

    Does Depth Affect the Hovering of a Neutrally Buoyant Object?

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  11. H

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  12. F

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  13. H

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  14. H

    How to Calculate the Longitudinal Center of Buoyancy for a Blimp Model?

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  15. T

    True/False -ish question, buoyancy

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  16. Boxlife27

    Calculating Tension & Buoyancy in Water

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  17. S

    Can electrolysis provide buoyancy to submerged machines?

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  18. W

    Buoyancy of a piece of wood floating in water

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  19. P

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  20. J

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  21. P

    Does Inhaling Air Increase Your Weight on a Scale?

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  22. K

    Buoyancy Situation Doubt - Archimedes Principle

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  23. Z

    FBD of Hot Air Balloon and Buoyancy

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  24. J

    Calculate Raft Buoyancy Depth | Density, Volume & Pressure Formula

    Homework Statement A raft is constructed of wood having a density of 625 kg/m^3. It's surface area is 5.5 m^2, and it's volume is 1.5 m^3. When the raft is placed in fresh water (denistiy = 1000 kg/m^3), to what depth, h, is the raft submerged under the water? Homework Equations P =...
  25. R

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  26. E

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  27. P

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  28. V

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  29. A

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  30. A

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  31. M

    Basic Buoyancy problem and analysis help

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  32. T

    Buoyancy Correction: Is Equation 1 Correct?

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  33. P

    How to Approach Buoyancy Force in Fluid Mechanics Homework?

    Homework Statement I've attached the problem I'm kind of lost as to how to even start this problem. For part ) I think my first approach is to sum up forces in the vertical direction. Which would yield F-W1-W2=ma=0 Where: F=buoyancy force W1=weight of submerged volume of oak...
  34. G

    Buoyancy to find mass, density and force to submerge

    Homework Statement A plastic cube, 200mm x 200mm x 200mm, is left in a cylindrical container that has a diameter of 400mm holding sea water, density 1024kg/m^3. The level in the container increases by 30mm as the block floats. i) Find the mass and density of the cube. ii) Find the extra...
  35. M

    Buoyancy Problem: Slab of Ice on Water

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  36. M

    Understanding Buoyancy: The Role of Object Shape and Archimedes' Principle

    I had read that, according to Law of Buoyancy/Archimedes Principle, "Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object." But does that depend on the shape of the object immersed? I see, that a metal block...
  37. M

    Is T=PV-M the Correct Formula for Calculating Buoyancy in Water?

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  38. M

    Is a 15kg object capable of generating 147N upward force in water?

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  39. shinnsohai

    Buoyancy and Archimedes's Principle Based Question

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  40. M

    Air pressure at water depth and buoyancy

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  41. M

    Buoyancy - Maximum mass a styrofoam sphere can hold in water.

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  42. M

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  43. K

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  44. K

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  45. S

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  46. H

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  47. F

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  48. J

    Conceptual Question about Buoyancy

    Say that I have two objects of the same mass and volume. I place one into freshwater and another in glycerine. In both cases, the objects are floating. Would the buoyant force from both of these fluids acting on the object be the same? From my understanding, buoyant force measures the weight...
  49. I

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  50. S

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