Buoyancy & Density Lab
Drag objects into fluid and see when they float or sink, with the buoyant force.
Drag the block into the water and let go. Change the fluid or the block's density and watch it float or sink.
About the Buoyancy & Density Lab
Free buoyancy simulator. Drag blocks into a tank, change the fluid and object densities, and see the buoyant force, weight, water displaced, and whether it floats or sinks. Built for physics, the buoyancy & density lab runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Drag objects into fluid and see when they float or sink, with the buoyant force. Use it to explore physics ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Buoyancy & Density Lab
- Use the controls to change Fluid, Object material, Object density, Block size. The simulation reacts instantly.
- Pick an option such as Oil (800), Water (1000), Salt water (1030), Mercury (13600) to switch modes or load an example.
- Press "Lift it out" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Drop a wood block, then a brick, into water.
- Change the fluid to oil, then saltwater, and watch the depth change.
- Adjust the object density until it just floats.
- Press it down and let go.
Key ideas you can learn
- Buoyant force equals the weight of the fluid displaced (Archimedes' principle).
- An object floats if its density is less than the fluid's.
- A floating object displaces water equal to its own weight.
Where this is used in the real world
Buoyancy explains ships, submarines, hot-air balloons, life jackets and how fish control depth.
Who is this simulation for?
Physics students in middle school, high school and first-year university, teachers who want a quick demonstration for the projector, and anyone revising for exams. It works well for flipped classrooms because students can explore before the lesson.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
Why do things float?
The fluid pushes up with a force equal to the weight of the fluid the object displaces. If that is at least the object's weight, it floats.
Why does a steel ship float?
Its hull encloses a lot of air, so the ship's average density is less than water. It displaces enough water to support its weight.
Is the Buoyancy & Density Lab free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Buoyancy & Density Lab work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.