gas laws Phase transitions
Age Group
12 13 14 15 16 17 18
Expected time
3 periods
A flower hidden by the cold.PDF
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A flower hidden by the cold

What’s the mystery? A toy balloon filled with air is immersed in liquid nitrogen and the air seems to disappear: the balloon shrinks completely. The air seems to have disappeared.
Domain(s) Physics
Subdomain keywords Phase transitions, gas laws.
Age group 12 to 18 years old.
Expected time for the mystery Approximate time for teacher preparation: one hour.Approximate time in classroom: three or four individual 50-min lessons.
Safety/supervision Liquid nitrogen requires local health and safety precautions and pupils should be supervised at all time during its use.Disclaimer: the authors of this teaching material will not be held responsible for any injury or damage to persons or properties that might occur in its use.
Preparation and list of materials Dewar with liquid nitrogen, toy balloons, air pump, toy balloon filled with helium gas, cryogenic gloves, syringes with one end plugged, temperature sensor, weights, supports for syringes, electric hotplate, thermal cups, glycerol, graduated cylinder (at least 60-70cm height), thin plastic tube (usually used for aquariums).
Learning objectives - Qualitative graphical representation of a certain thermodynamic variable in the function of another: in particular, representation of the volume of a gas as a function of the temperature or pressure.- Introduction to phase transitions.
Resources To become familiar with the most common phase transitions, it is possible to observe what happens for water. This video shows how the phases depend on temperature:

In the following video, the dependence of the phase on the pressure is shown: