manual

24
Air is made up of lots of gaseous particles that exert
pressure in all directions.
The index card creates a large surface area where air can push up. Now the
atmospheric pressure pushing up on the card is greater than the force of
the water pushing down.
The gas particles exert pressure in all directions, even from the bottom,
keeping the card pressed onto the edges of the glass.
There is more pressure
pushing up than down.
A barometer is an instrument we use
to measure air pressure.