What you need:
A plastic bag
A rubber band
A glass jar which can accommodate your hand
What to do:
1. Stuff your hand into the plastic bag and turn it inside out. Is it easy?
2. Now push the same plastic into the jar. Spread it out so that it lines the jar.
3. Fold the top of the bag over the mouth of the jar. Secure it real tight using the rubber band.
4. Now, put your hand into the jar and try to turn the plastic bag inside out again.
What happens:
When the plastic is unattached to the jar, it is easy to pull it inside out. But once the bag is secure, it becomes really hard to separate it from the jar (provided the seal of the rubber band stays in place).
Why?
Air exerts some pressure or push on everything. When you seal the plastic and the jar using the rubber band, there is a small amount of air trapped between them. But the empty jar is filled with more air than that. Thus, the push of the air trapped between the plastic and the jar is less when compared to the push of the air inside the jar. The air in the jar pushes the bag down, trying to hold it in place when you try to remove it.
Picture Credit : Google
