Materials:

Experiment:

Place the screen so that it covers the opening of the jar entirely and screw the lid on over the top of it. Pour water into the jar until it is filled. Place the card over the opening and tip the jar upside down. Remove the card and notice that the water stays in the jar. Even though it is upside down. If you tilt the jar a little bit, water will pour out of the jar until it is tipped vertically upside down again.

What’s happening?

In the March 2017 issue the demonstration showed how the card can hold water in an upside down cup and that was explained using air pressure. In the previous February issue, surface tension was used to explain how the addition of paper clips to a filled cup of water seemed to defy logic.

This is another application of the same principles. Again, water stays in the jar with the card being held on by the air pressure pushing up on the card and only the mass of the water pushing down on the card. This time when you remove the card, the screen has small enough openings that the surface tension of the water is able to prevent the water from flowing through the screen openings – think of the polar water molecules holding hands and stretching across the distance of one side of the screen to the other.

References:

https://www.flinnsci.ca/api/library/Download/95bd5ebf4af246279195f4d633f7802b

To view all past “ChemShorts for Kids”, go to: http://chicagoacs.org/ChemShorts

Paul Brandt