Floating, sinking and upthrust sim
Lower a cylinder on a newton-meter into water, salt water or cooking oil from a displacement can that spills into a beaker on a balance: watch the reading fall as the upthrust grows, find U = weight in air − reading in the liquid, predict float or sink from the densities, and see a wooden block float deeper in oil and higher in salt water; cards show a hydrometer and a steel boat.
Density and pressure · covers the IGCSE, GCSE topic
What the sim shows
Model: the liquid pushes up on the cylinder with an upthrust U = ρ g a d, where d is how much of its height is under the surface and a its end area (the pressure on its bottom face is bigger than on its top face); once all of it is under, U stays the same however deep it goes. The newton-meter (0 to 10 N, 0.1 N divisions) holds up the rest: it reads W − U, plus any zero error. g = 10 N/kg. Every object is 100 cm³ (radius 20 mm, 79.6 mm tall): aluminium 270 g, brass 850 g, beech 70 g. Liquids: water 1000, salt water 1100, cooking oil 920 kg/m³. The can is filled until liquid runs out of the spout; what the cylinder then pushes aside runs into the beaker, and the balance reads it to 0.1 g once zeroed with the empty beaker on it. Idealised: the liquid runs out at once (in class, wait for the dripping to stop), a film of 0.2 to 0.8 g stays on the spout at each fill (seeded), the meter sticks by up to ±0.03 N (seeded) before you read it to the nearest division, the thread has no weight or volume, the spring's stretch does not move the cylinder, no liquid clings to it, and the floating block stays upright. Drawn to scale; the clamp moves in 1 mm steps.
- The hanging cylinder: the part to watch
- Newton-meter on a clamp, displacement can, beaker on a top-pan balance, spare cylinders, stock bottle
Use it in your lessons
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