NovaMath

What affects buoyancy

Required: F = ρ_fluid g V_disp; float / suspend / sink.

Buoyancy (junior)Archimedes’ principle and floating/sinking.

Start here

What affects buoyancy

Required lab: what affects buoyancy? Weighing Fb = G − F_scale and Archimedes Fb = ρ g V_disp. Once fully immersed, depth does not change Fb. Tune the tank in the browser.

Memory cue: Fb = ρ g V_disp · Fb = G − F_scale · fully immersed ⇒ depth independent.

Key formulas

  • Fb = ρ_liq g V_disp
  • Fb = G − F_scale (weighing)
  • Fully immersed: Fb independent of depth

How to use

  1. Read Start here and Related knowledge (map + §§1–3).
  2. In Hold mode, change immersion and liquid density; watch Fb, G, F_scale.
  3. When fully immersed, vary extra depth (Fb stays constant), then Release to see float/sink.

Read next

Related knowledge

Read concepts → weighing → factors → Archimedes → methods & pitfalls — and check Fb = ρ g V_disp and Fb = G − F_scale on the tank.

Mind map

1. What is buoyancy

An object immersed in a liquid (or gas) feels an upward supporting force — buoyancy. It always points vertically up. The fluid exerts the force; the immersed object receives it.

Cause: pressure difference between top and bottom faces. Side faces cancel; deeper bottom means larger upward force, so Fb = F_up − F_down. No liquid under the bottom (e.g. a pile driven into the riverbed) → no buoyancy.

2. Weighing method

Kit: spring scale, sample, beaker, water, string. In Hold mode here, the hanging dynamometer shows F_scale.

  1. Measure weight G of the sample in air.
  2. Immerse the sample and read the scale F_scale.
  3. Buoyancy: Fb = G − F_scale.
  • Fb = G − F_scaleWeighing: weight in air minus scale reading in liquid.

3. What affects buoyancy

Buoyancy depends on immersed volume and liquid density — not on depth once the object is fully immersed.

  • Larger displaced volume V_disp → larger Fb.
  • Larger liquid density ρ_liq → larger Fb.
  • After full immersion, extra depth does not change Fb or F_scale (common pitfall).

4. Archimedes’ principle

An immersed object feels an upward force equal to the weight of the fluid it displaces. The same idea holds for gases.

  • V_disp is the immersed part of the volume, not always the whole object.
  • Fully immersed: V_disp = V; partially: V_disp < V.
  • Fb depends only on ρ_liq and V_disp — not on object density, shape, or depth when V_disp is fixed.
  • Fb = G_disp = ρ_liq g V_dispFb in N; ρ_liq in kg/m³; g ≈ 9.8 or 10 N/kg; V_disp in m³.

5. Ways to find Fb

  • Weighing: Fb = G − F_scale (hanging scale in liquid).
  • Pressure difference: Fb = F_up − F_down.
  • Archimedes: Fb = ρ_liq g V_disp.
  • Equilibrium: when floating or suspended, Fb = G.

6. Pitfalls & exam focus

  • Fully immersed: Fb independent of depth.
  • Same V_disp and ρ_liq → shape does not matter.
  • Materials denser than water can float if made hollow (ships) — see the float/sink lab.
  • Typical problems: compare Fb in different liquids; float/suspend forces; find density/volume; liquid-level puzzles with melting ice.

Applications

  • Ships and submarines balance weight and buoyant force.
  • Hydrometers and floating toys apply Archimedes’ principle.

FAQ

Does buoyancy depend on depth?

Before full immersion, deeper means larger V_disp and Fb. After full immersion, Fb does not change with depth.

How does the weighing method work?

Measure G in air, then F_scale in liquid; Fb = G − F_scale.

What equals the buoyant force?

Weight of displaced fluid: F_b = ρ_fluid g V_displaced.

Does deeper immersion always raise buoyancy?

Once fully submerged, V_displaced is fixed so F_b stays the same.

Try the lab