Gases under pressure

One sealed sample of air: 50 cm³ at 20 °C with only the atmosphere pushing on the plunger. Each disc weight adds a push equal to half the push of the atmosphere. Real weights would have to be far heavier: several kilograms each.

The volume is calculated from the temperature and the pressure for an ideal gas, with a perfect seal and a plunger that slides without friction. The water in the bath reaches above the plunger seal. The bath warms to 80 °C, or is refilled with ice and cold water at 2 °C; the air always reaches the water’s temperature before a reading is taken.

In a real syringe, squeezing quickly warms the air a little, and friction can make the plunger stick. Here the readings are already settled. The readings are simulated, not measured.

The magnified view shows far fewer particles than real air, drawn larger and much slower. The effect of pressure on their space is to scale. The effect of temperature is exaggerated about 4 times, so that you can see the particles speed up and spread out; a bigger flash means a harder hit. It always shows the same particles, because no air gets in or out.

A real hot water bath and hotplate need a teacher-approved safety procedure, and so do heavy weights on glass.

With reduced motion, the water bath jumps straight to its steady temperature and the particles are drawn still. Real particles never stop moving.