All Labs

Buoyancy Lab

Investigate Archimedes' principle by placing objects of different densities into fluids. Observe whether objects float or sink, measure buoyant force, and discover how density ratios determine how much of an object stays above the surface.

Guided Experiment: Floating and Sinking Investigation

If you place an object with density less than water into water, what fraction of the object do you predict will be submerged?

Write your hypothesis in the Lab Report panel, then click Next.

Controls

Object Density500 kg/m³
Object Volume0.0010 m³
Fluid Density1000 kg/m³
Gravity9.81 m/s²

Results

Object StatusFloating
Fb=4.9050 NF_b = 4.9050 \text{ N}
Object Weight
4.9050 N
Buoyant Force
4.9050 N
Apparent Weight
0.0000 N
Fraction Submerged
50.0%
Object Mass
0.5000 kg
Displaced Volume
0.00050 m³
ρobj=500 kg/m3ρfluid=1000 kg/m3\rho_{\text{obj}} = 500 \text{ kg/m}^3 \quad \rho_{\text{fluid}} = 1000 \text{ kg/m}^3

Buoyant Force vs Object Density

Data Table

(0 rows)
#TrialObject Density(kg/m³)Fluid Density(kg/m³)Buoyant Force(N)Apparent Weight(N)Fraction SubmergedFloats?
0 / 500
0 / 500
0 / 500

Reference Guide

Archimedes' Principle

Any object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces.

Fb=ρfluid⋅Vdisplaced⋅gF_b = \rho_{\text{fluid}} \cdot V_{\text{displaced}} \cdot g

Where ρ is fluid density in kg/m³, V is displaced volume in m³, and g is gravitational acceleration.

Buoyant Force

The buoyant force depends only on the fluid density and the volume of fluid displaced, not the object's material.

Fb=ρfluid⋅Vobj⋅g(sinking)F_b = \rho_{\text{fluid}} \cdot V_{\text{obj}} \cdot g \quad (\text{sinking})

For a sinking object, the full object volume is displaced. For a floating object, only the submerged fraction displaces fluid.

Floating and Sinking

An object floats when its average density is less than the fluid density. The fraction of the object submerged equals the density ratio.

f=ρobjρfluidf = \frac{\rho_{\text{obj}}}{\rho_{\text{fluid}}}

Ice floats in water with about 91.7% submerged because ice density (917 kg/m³) is 91.7% of water density (1000 kg/m³).

Apparent Weight

A submerged object feels lighter because the buoyant force partially opposes gravity. This reduced force is called apparent weight.

Wapp=mg−Fb=mg(1−ρfluidρobj)W_{\text{app}} = mg - F_b = mg\left(1 - \frac{\rho_{\text{fluid}}}{\rho_{\text{obj}}}\right)

A neutrally buoyant object (equal densities) has zero apparent weight and hovers motionless in the fluid.