060 – Air pressure demonstration

Trapped water  

Introduction to:

Pressure, air pressure, hydrostatic pressure  

Materials: 

• Drinking glass 
• Sheet of paper/paper towel/piece of toilet roll 
• water 

Setup and execution:  

• Fill a drinking glass to the brim with water.  
• Place a sheet of paper or a paper towel on top.  
• Make sure that no air is trapped. 
• Carefully turn the glass upside down.  

 Observation:  

•  The water stays in the glass. 

Explanation:  

The air pressure presses on the paper from below, and the hydrostatic pressure of the water from above. However, this is much smaller, since only a 10 meter high water column generates a pressure of one bar, which would be able to compete with standard air pressure.