Archimedes’ principle
How much is submerged, how much is displaced, and how large is the buoyant force?
The buoyant force equals the weight of the liquid displaced. Before the object is fully submerged, the buoyant force grows with the displaced volume; once it is fully submerged, pushing it deeper does not change the buoyant force. In this experiment an external force holds the object at the chosen submerged fraction, making the buoyant force easy to observe.
Buoyant force vs. submerged fraction
Think about it
When an object with a density of 800 kg/m³ floats in water, what fraction of its volume is submerged?
80%. When floating, the buoyant force equals the weight, so V_disp/V_obj = ρ_obj/ρ_water = 800/1000. Set the liquid density to 1000 and the submerged fraction to 80%, and the required external force drops to zero.
Model assumptionsObject density 800 kg/m³ · g = 9.8 m/s² · held in place by an external force · surface tension ignored · free floating and sinking not simulated
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.