Although air is invisible, it still takes up space and is made of molecules. There is more space between the air molecules in a room than the air molecules in a balloon, for example. Under high pressure, air molecules are more densely packed. Under low pressure, air molecules are less densely packed. When you blow into the bottle in this activity, air is compressed and air pressure inside the bottle increases.
Air moves from areas of high pressure to areas of lower pressure as the air molecules attempt to spread out. For example, if you let go of a balloon that you have blown up but not tied, the air rapidly exits. The air is moving out of the balloon to an area of lower pressure. The greater the difference in pressure, the faster the air will move. The air blown into a bottle is a lot like air blown into a balloon. If it’s not trapped, it will rush out of the bottle toward lower pressure. Consequently, the paper is pushed out of the bottle instead of into it.
In the atmosphere, air moves toward low pressure and its motion is also influenced by the spin of the Earth. This is called the Coriolis Effect and causes air to move counterclockwise around low pressure in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Air pressure records:
- United States
- Highest: 31.85 inHg (1078.8 mb) in Northway, Alaska, on January 31, 1989
- Lowest: 25.10 inHg (850 mb) in Manchester, South Dakota, on June 24, 2003 during an F4 tornado
- Highest: 32.06 inHg (1084.8 mb) in Tonsontsengel, Mongolia, on December 19, 2001
- Lowest: 25.69 inHg (870 mb) in the Philippine Sea in the southwestern Pacific Ocean during Typhoon Tip on October 12, 1979