Do and observe!

In order to perform this experiment, you will need a glass and a piece of wax baking paper (the test will also yield good results if you use a playing card instead of the wax paper). This is an experiment with water, which is why it should be conducted over a bathtub or a sink!

Hold the glass in your hand and fill it with water to the top, carefully laying a piece of wax paper over it. Then place the palm of your other hand over the paper and quickly turn the glass upside down and remove your palm.

What happened?

The water from the glass will not fall out, even though the glass is turned upside down. It seems as though the paper is strong enough to hold the water in the glass. Is it really the paper holding the water in the glass?

We live on Earth and breathe air. However, there is no air in space – only a vacuum. Air surrounds the Earth like a sort of a wrap. We live at the bottom of this air. Air has its own weight and exerts pressure on us from all sides. The pressure applied is the same as the force of 10 metres of water above us.



Therefore, air also exerts pressure on the wax paper, while the water in the glass exerts pressure on the paper on the other side. However, there is only about a decimetre of water in the glass, while the air on the other side applies a pressure equalling the force of 10 metres of water.
Because of this, the water stays in the glass.

More...

Why does the water leave the glass if the glass is not covered with paper and is merely turned?
At that point, the air, which is thinner than the water, can penetrate the glass and the water flows out. This is actually good news! Imagine pouring juice into a glass and not being able to drink it, because the juice does not want to flow out.