This week's experiment is a simple one. It is one of those things that you have experienced over and over, but might not have thought much about. To try it, you will need:

- a freezer
- some ice cream (Optional for some people. Required for me.)

First, open the freezer, remove the ice cream, and close the door. Now for the difficult part. Immediately, open the door and put the ice cream back.

You will probably notice that it is much harder to open the freezer door the second time. Why? It is not just because you want to keep the ice cream. It is definitely more difficult to pull the door open.

The air inside the freezer is cold, which makes it more dense than room temperature air. When you open the freezer that cold, dense air flows out, and is replaced by lighter, warmer air. When you close the freezer door, the air inside gets colder. As its temperature falls, it contracts, which creates a lower air pressure inside the freezer. When you try to open the door the second time, the higher air pressure outside is not balanced by the pressure inside. Since there is more pressure pushing in, if it much harder to open the door.

If the experiment does not work well for you, try removing some of the frozen foods from your freezer. The more air space that you have, the better the experiment will work. If it still does not work well, examine the seal on the freezer door. If the seal is broken or damaged, it would let air in to equalize the pressure. That also means that it is letting the cold air flow out of your freezer, which is not good.

Now, the second time that you open the freezer door, it is not really necessary to put the ice cream back. It is perfectly OK to keep it out long enough to scoop some into a bowl. That will let you test to see whether the pressure has equalized by the time you finish eating, and go back for seconds.

Have a wonder-filled week.