2. BUOYANCY

• 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 F_B
  • 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:
    1. The pressure on the bottom of an object is greater than the top
       (since pressure increases with depth).
    2. The force on the bottom pushes up and the force on the top pushes down
       (since force is normal to the surface).
    3. The direction of the net force due to the fluid is upward.

https://phet.colorado.edu/sims/density-and-buoyancy/buoyancy_en.html

• Archimedes’ Principle

  The magnitude of the buoyant force on an object is equal to the weight of the fluid it displaces.

  F_b = V_immersed × d × g

  • The factors that affect buoyancy are…

• • • the volume of the fluid displaced,
    • the density of the fluid, 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.

• Objects immersed in a fluid have an apparent weight that is…
  • reduced by the buoyant force (less than their actual weight)

    W′ = W −F_b

     (W′ < W)

  • directly proportional to the relative density (d′ = d_object − d_fluid)

    W′ = d′gV

  Densities	Fb> Wobject	Fb= Wobject	Fb< Wobject
  dobject < dfluid	Object rises (wholly immersed )	Float on surface (partly immersed)
  dobject = dfluid		Neutral buoyancy (wholly immersed)
  dobject > dfluid			Object sinks