Do only under adult supervision. Never operate a pressure cooker without safety release valve, and never operate a pressure cooker without a thorough knowledge of its operation. Never attempt to open a pressure cooker while it is hot. Improper use of the pressure cooker can results in serious injury.
Place about an inch of water in the pressure cooker, and place within a styrofoam cup open end down. If you want, you can draw a design on the cup.
Replace the lid with the pressure relief valve and heat on the stove for 10 minutes.
Remove from heat and allow to sit for 1 hour before opening. Or you can run water over the pressure cooker to reduce the heat and pressure.
Open and remove the cup. Observe. The time of heating may need to be adjusted to allow for best results.
IMPROVEMENT: I also got it to shrink more when the styrofoam cup is out of the water. So fill the pressure cooker about 1/2 to 1 inch water, then place a Corningware bowl on a metal grate. Then place the styrofoam cup in the bowl, as it shrinks better when it is not in water. Then put on the lid and on the stove. Once it starts to hiss start your timer for 10 minutes.
The results of this experiment are amazing. The styrofoam cup shrinks to an amazingly small size, yet is a perfect replicas in every way of an undisturbed cup. This incredible effect is due to the fact styrofoam cups are blown up with gas, and when the gas diffuses out, the spaces fill up with air. This greatly enhances its insulating ability. The volume of this air is greatly reduced by the high pressures within the pressure cooker. As a result. much of this air is forced out, causing the cup to shrink to much smaller size.
Pressure cookers work by not allowing steam to escape, which builds up to a tremendous pressure. Water thus boils at temperature much higher than 100 C. As a result, foods can cooke much faster.
Pressure cookers are especially useful for cooking at high altitudes, where the boiling point of water is lower due to less air pressure. A combination of high pressure and intense heat shrinks the styrofoam cups.
The same effect has been observed when styrofoam cups are submerged in the depths of the ocean. The intense pressure of the water compresses the air in the cup and drives it out. This is verification of come on you guys should know…Boyle’s law, since an increase in pressure results in a decrease in volume.