The porous pot sim

What the sim shows

Gas passes the unglazed pot's wall through its tiny pores, both ways at once. Each gas diffuses at a rate inversely proportional to √Mᵣ, so hydrogen (Mᵣ 2) gets in √(44 ÷ 2) = 4.69 times as fast as carbon dioxide (Mᵣ 44) gets out. The pot gains particles, its pressure rises and the water is pushed down on the pot side: here by up to 43 mm, 12 s after the beaker goes on. As the gases even out the levels come back together. Lift the beaker off and the hydrogen in the pot diffuses out faster than air comes in, so the pressure falls below the room's. With the same gas inside and out, nothing happens: a control. Air is taken as one gas of Mᵣ 29 (its mean). The gas volume is 41.2 cm³ (pot 29.8, tube 2.3, U-tube limb 9.2). How fast gas passes this wall (air: 0.3 cm³ a second for a full atmosphere's difference) and how easily the pushed gas flows back through the pores are this desk's estimates; the beaker is taken as staying full of its gas. The level difference is the pressure difference ÷ (1000 kg/m³ × 9.81 m/s²). The clock runs 10 times faster than real time.

Use it in your lessons

• Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
• Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
• Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.

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