Life under pressure: air pressure.

We live under a blanket of air. Though we don't often think about it, that air has a tremendous weight. Every object on the surface of the earth has this force exerted upon it in the form of air pressure. 

Think about a stack of books. Which book has the most weight (force) exerted on it?  The one at the bottom.  Air pressure works the same way.  The higher someone is, the less air above them weighing down. At sea level, average air pressure is approximately 15 pounds per square inch! 

Air Pressure Activity

Materials: Gather an empty, clean plastic milk jug with cap, funnel, hot water, a bowl with ice water.

Activity: 

• With the help of an adult, heat some water to boiling.
• Take the cap off the milk jug, and use a funnel to pour the hot water into the jug.
• Once you have about 2 inches of water in the jug, shake the jug gently for one minute, making sure not to spill any water.
• At the end of the minute, place the cap back on the jug tightly. 
• Place the jug in a bowl containing an inch of ice water. 
• Watch what happens.

Explanation: When hot water is added to the jug, it heats the air, which escapes through the opening. Once the cap is replaced and the air inside the jug cools, air pressure inside the jug becomes less than outside the jug, so it collapses.

• Lungs work by using muscles to expand our chest, lowering air pressure in our lungs and allowing outside air in. 
• When jet airplanes fly at high altitudes, the air pressure is much lower (the higher you are, the less air weighing down on you).  Air pressure inside the plane must be kept much higher than outside the plane, so that we can breathe.

Dig Deeper: Watch this video: ">What Makes the Wind?