# What is air pressure? Part 1

WHAT IS AIR PRESSURE?
Contributed By: Buzzy B.
Date of Publication: 9/30/11
Air pressure is the weight of the air from sea level, all the way up to the tip of the atmosphere. You are feeling air pressure all the time. You aren’t just feeling air pressure from above, you are feeling air pressure from all around you. People are used to air pressure. We are so used to it in fact, that we don’t even recognize that there is air pressure. Air pressure is much higher near the sea level because there is so much more air above you. Air pressure isn’t as high on a place like a mountain that has a high altitude. You are under very high air pressure, about 14 pounds per square inch, meaning every square inch of surface area is being pushed in all directions by about 14 pounds of pressure. The only thing that is saving you from being squashed is the fact that you have air inside of you that is pushing out, so the forces equal themselves out.
Air pressure can be used to tell what weather is coming. Usually when the air pressure is rising, it means that the area will have nice weather, and there won’t be any rain. When the air pressure is lower, it usually means that there will be rain. The air pressure is commonly determined by meteorologists to help tell what the weather will be like.

Figure 1: This explains the difference between high air pressure and low air pressure.

Hot Air Balloons
Hot air balloons float because the hot air is less dense than the cool air, which means that the hot air is lighter than the cool air. That hot air rises to the top, and pushes up on the balloon making it rise. One problem with the hot air balloon is that one cubic foot of hot air only lifts 7 grams, so it takes 65,000 square feet of hot air to lift 1,000 pounds, that’s why the balloons Have to be so huge. Another problem with hot air balloons is that they can’t really steer. So hot air balloons aren’t really a good source of transportation, unless you just want to see the scenery.

Barometers
Barometers are also closely related to air pressure. They are usually used to measure air pressure in certain locations. They can measure the air pressure by using different substances. Some examples are water, air, or even mercury. They can be quite helpful with tracking storm systems, and are commonly used among meteorologists. Barometers measure the air pressure in millibars. The more millibars the dryer the air is.

Figure 2: A barometer is used to measure the air pressure.

GLOSSARY
Air Pressure- The force per unit area that the air exerts on any surface.
Barometer- An instrument used for measuring the atmospheric pressure.
Hot Air Balloon- Balloon for travel through the air in a basket suspended below a large bag of heated air.
Millibar- A unit of atmospheric pressure equal to one thousandth of a bar.
Atmosphere- The gaseous envelope surrounding the earth; the air.

CITATIONS
• "atmospheric pressure." Encyclopædia Britannica. Encyclopædia Britannica Online School Edition.
Encyclopædia Britannica, Inc., 2011. Web. 19 Sept. 2011.
<http://school.eb.com/eb/article-9010121>.
9/13/11. Web. 9/20/11.