Physic Labs

Fluid mechanics

Archimedes' buoyant force and floating

Compare weight with Archimedes' force F_A = ρ_water g V_submerged and identify the conditions for floating, suspension, and sinking. Measure buoyant force and displaced-fluid volume, then verify FA=ρfluidgVdisplacedF_A = ρ_{fluid}gV_{displaced}.

Middle school

⚠ The water tank is simulated; keep electrical equipment away from water during real experiments.

Equipment

  • Virtual water tank with a solid object and force vectors
  • Object-density ρ_object and volume V sliders; material presets

Procedure

  1. Move from floating to sinking

    Start with ρ_object below 1000 kg/m³ (water), then move the density slider across 1000 kg/m³. Observe the submerged fraction and the vectors for weight P, buoyancy F_A, and support N if the object reaches the bottom. Change V to see the forces scale even though floating depends on relative density. Material buttons simply set the corresponding ρ value. Compare the observed quantities with FA=ρfluidgVdisplacedF_A = ρ_{fluid}gV_{displaced}.

  2. Compare buoyancy with weight

    Use the selected ρ and V to calculate the weight of displaced fluid. Compare it with the on-screen buoyant-force vector using FA=ρfluidgVsubmergedF_A = \rho_{fluid}gV_{submerged}; check that a floating object has buoyancy balancing its weight.

  3. Change the submerged volume

    Keep relative density fixed while changing V, and observe buoyancy and the submerged fraction. Compare readings and explain why volume changes force magnitude while floating, suspension, or sinking depends on density and net force. Compare the observed quantities with FA=ρfluidgVdisplacedF_A = ρ_{fluid}gV_{displaced}.

Simulation

Experiment history

Archimedes of Syracuse (c. 287–212 BCE) worked in mathematics, mechanics, and hydrostatics. Stories about him were transmitted by ancient writers centuries later, so the famous “Eureka” episode cannot be treated as a contemporary record. His surviving treatise On Floating Bodies is among the ancient works that established a mathematical foundation for the equilibrium of bodies in fluids. Archimedes' principle states that a body partly or wholly immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced. Thus buoyancy depends on submerged volume and fluid density, while equilibrium compares the buoyant force with the body's weight. The modern formula is a hydrostatic expression of this classical result.

Related physicists

Archimedes of Syracuse

Related library topics

Archimedes’ principle