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Understanding Buoyancy

  • Upthrust = Weight of Displaced Fluid = Volume x Density
    • So it is about relative density
  • If the bottom has no pressure to form a difference, there is no buoyancy. For example, in suction cups.
  • But why is the water at the bottom pushing upwards?
    • Pressure is the volumetric energy of the particles in the fluid
    • Technically, you can apply this to solids too, as energy per unit volume is the normal force per unit area.
    • For air, the energy is due to the collisions of the number of particles, due to compression increasing the number of particles per unit volume
    • For fluids and solids, the energy due to the restorative forces, acting like compressed springs, due to incompressibility
    • Because of the energy, it exerts a force on the body, pushing on it in the normal direction(s)
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