Archimedes' Principle – Floating, Sinking and Liquid Pressure
Integrated ScienceForces & MotionAges 13–14
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Forces & Motion
Drag a block and drop it into a tank of liquid: it sinks, floats in equilibrium, or rises to the surface depending on its density compared with the liquid. The weight arrow W and the upthrust arrow F_B = ρ·g·V_submerged change length with the submerged volume; drag the pressure probe up and down in the liquid to see p = ρ·g·h increase with depth. The readouts and the floating/sinking conclusion update continuously.
Lesson: Archimedes' Principle; Liquid Pressure; Density
What it shows
An object in a liquid feels an upward force, the upthrust or buoyant force, equal to the weight of liquid it displaces: F_B = ρ_liquid·g·V_submerged, with g = 9.81 N/kg. Its weight is W = ρ_object·g·V. Whether it floats, stays suspended or sinks depends on comparing the two densities, not on size alone. A floating object settles where just enough of it is below the surface for F_B to equal W. The same liquid exerts a pressure that grows linearly with depth, p = ρ·g·h, whatever the shape of the tank.
How to use
Set the Density of the object and the Density of the liquid, press Drop Object and watch the W and F_B arrows as the block enters the liquid. Note the submerged volume when the block comes to rest and compare it with the ratio of the two densities. Try a dense metal in water, then raise the liquid density towards that of mercury. Finally, drag the pressure probe downwards and record p at several depths to plot pressure against depth.
Parameters you can change
- Density of the object 100–12000 kg/m³
- Density of the liquid 500–13600 kg/m³
- Volume of the object 50–1000 cm³
- Liquid column height 20–100 cm
- Show force vectors
Questions to explore
- A block of density 600 kg/m³ floats in water. What fraction of its volume is submerged, and why?
- When a block floats at rest, is the upthrust greater than, equal to or less than its weight?
- How does the pressure reading change when you double the depth of the probe in the same liquid?
