About this simulation
Draw an object, drop it into a tank of liquid and see whether it floats. Your drawing is a slice through an object 10 cm deep, so every mass and force is in real units.
Key ideas
- Archimedes' principle: the liquid pushes up with the weight of the liquid the object displaces: Fb = ρliquid g Vsubmerged.
- Density decides: an object floats if its average density is below the liquid's, with that fraction of it under the surface: pine (500 kg/m³) floats half under water, and steel sinks in water but floats on mercury.
- Hollow things float: sealed air (hatched) and the air in an open hull add volume but hardly any mass. Once water pours over the rim, the hull fills and sinks.
- Stability: weight acts at the centre of mass, buoyancy at the centre of the submerged part. If a tilt moves the buoyancy to the low side, the object rights itself.
Things to try
- Drop the steel boat, then drag one side under until it swamps.
- Drop a steel block in water, then switch the liquid to mercury.
How to use it
Pick a material and a tool and drag on the tank to draw (a finger works too), then press Drop. Drag the object to lift or throw it (on a touchscreen, hold it with two fingers to turn it), or tap the liquid for waves. opens the settings: liquid, ready-made objects, force arrows and gravity. With a keyboard, the arrow keys move between materials and between tools, and Ctrl+Z undoes.
The model is 2D: every 1 cm cell is cut along the liquid surface to find exactly what is submerged, and liquid inside a hull keeps a level surface and flows through its openings. Drag and waves are included; swirling flow is not.