Pressurised Drinks Cans

• A bunsen burner and tripod (or cooker).
• A large beaker of cold water (or bowl of cold water).
• Tongs (or something to pick up the hot can with).
• An empty drink can.

1. Pour a tablespoon of water into the empty drink can.
2. Place the can on the tripod above the lit bunsen burner: have it hot enough to not create soot all over your can, but not so hot that the water boils too quickly. If you are going to put it on a cooker to heat it up, make sure there is no plastic or paper attached that could melt onto the surface.
3. Let the water boil and mostly turn into steam, but don't let the can boil dry. It should take about 30 seconds. You'll know when it is boiling because steam will start to come out the top.
4. Turn the bunsen burner (or cooker) off then lift the can off with the tongs. BE CAREFUL - IT WILL BE HOT.
5. Turn the can upside down. BE CAREFUL - IT WILL STILL CONTAIN SOME VERY HOT WATER WHICH MAY SPLASH OUT.
6. Place the upside down can quickly in your beaker or bowl of cold water.
7. Watch as the can crumples.

Heating the can makes the water inside it boil, turning this liquid into gaseous water vapour. The water vapour adds to the number of gas molecules inside the can and pushes some of the air out of the can. The escaping air and water vapour keeps the pressure inside the can the same as the pressure outside. If the air hadn't escaped (perhaps if the can was sealed) the can would have started to inflate (just before it exploded!).

Putting the can upside down in the cold water seals the can; no more air can flow into it. Instead, the water vapour inside the can cools down as the sides of the can cool in the cold water. This gaseous water vapour turns back into liquid water and the pressure is reduced in the can. With no air able to flow back into the can, there is an imbalance between the air pressure outside the can and inside. The pressure outside pushes on the can until the can crumples.

The can will stop crumpling once it has reached a volume where the pressure inside equals the pressure outside (or that it is squeezed so tightly that the force from the air pressure can't deform it any further, but really you need a vacuum pump for that!).

Use protective eyewear when working with hot liquids and a bunsen burner. Don't touch the can with your hands whilst it is heating and when you are putting it into the cold water. Also be aware that the can and any remaining liquid in it will be warm. Do not touch the crumpled can until you are sure it is cool.