Practice

Fb = ρVg Formula – Buoyancy Practice

Fb = ρVg — Buoyant force (Archimedes)

The buoyant force equals the weight of the displaced fluid: Fb = ρVg, where ρ is fluid density and V is displaced volume.

Guide — how to use this formula

1. 1. Identify fluid density ρ and displaced volume V.
2. 2. Fb = ρVg; rearrange for V, ρ, or g.
3. 3. Floating: Fb equals the object’s weight.
4. 4. Convert litres → m³ when needed (1 L = 0.001 m³).

Derivation

Archimedes’ principle: upward force equals weight of fluid displaced:

1. Weight of displaced fluid:
   W_{\text{fluid}} = m g = \rho V g
2. Buoyant force:
   F_b = \rho V g

Use fluid density, not object density, in Fb = ρVg.

Examples

Example: water, V = 0.05 m³, g = 10

Fb = 1000×0.05×10 = 500 N.

Example: find V

Fb = 2000 N, ρ = 1000, g = 10 → V = 0.2 m³.

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