Can you feel the pressure? It’s around you…all the time…everywhere you go. What is it? Atmospheric pressure — often referred to simply as air pressure — is the constant force exerted on you by the weight of little particles of air.

These tiny air particles, called air molecules, can’t be seen, but they are all around you. They have weight, which means they constantly “push” down on you. If you look straight up in the air, you can imagine a tall column of air above your head reaching all the way to the edge of the Earth’s atmosphere.

The weight of that column of air is the amount of air pressure exerted on you. If you move to a higher elevation (climb a mountain, for example), the air pressure will be lower. Why? The length of that column of air above you has decreased by the amount of your increase in elevation.

As you move to a higher elevation, you may notice that your ears have to “pop.” This balances the pressure between the inside and outside of your ear. Since there are fewer air molecules the higher you go, you will also probably need to breathe faster to breathe in more molecules to make up for the deficit.

Air molecules also take up space. Because there tends to be a lot of empty space between air molecules, air can either fill a big area or it can be compressed to fit into a smaller area. When it’s compressed, air is said to be under high pressure.

Earth’s atmosphere presses down on you with a force of almost 15 pounds per square inch. You may be wondering why it doesn’t feel that heavy or why you’re not crushed under the weight. Remember that thing you do called breathing?

The air inside your body balances out the pressure from air in the atmosphere, which prevents you from being squished by the pressure of the atmosphere. You don’t sense air pressure as a constant force, because the air inside you balances outside pressure and you’re used to that feeling.

If you watch the weather report frequently, you’re sure to hear the weatherman talk about barometric pressure. Weather forecasters use a special tool called a barometer to measure air pressure.

Barometers measure atmospheric pressure using mercury, water or air. You’ll usually hear forecasters give measurements in either inches of mercury or in millibars (mb). Forecasters use changes in air pressure measured with barometers to predict short-term changes in the weather.

Changes in air pressure signal the movement of high- or low-pressure areas of air, called fronts. Air molecules in high pressure areas tend to flow toward low pressure areas. We call this flow of air molecules wind. The larger the difference in pressure between areas, the stronger the winds will be.

As weather forecasters monitor air pressure, falling barometer measurements can signal that bad weather is on the way. In general, if a low pressure system is on its way, be prepared for warmer weather with storms and rain. If a high pressure system is coming, you can expect clear skies and cooler temperatures.

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    • Wow, :D! That’s a lot of weather instruments…thanks for sharing them! Looks like we might have some more weather Wonders in our future! :-)

    • Hey there, Wonder Friend! Thanks for sharing your comment– be sure to check out our Wonder video and article to help you answer your question! We are glad you enjoy visiting Wonderopolis and we cannot wait to see you again! :)

    • Thanks for responding, Wonder Friend F! We Wonder what you learned from our weather Wonder! Did you find the answer to your awesome question? :)

  1. Yes I did and may I add you have such a good website that I am recommending to my friends!
    Also, If you could have a video on sugar cane that would help a whole lot! <:)

    Recommending always,
    Wounder Friend F

    • Great question, Wonder Friend! We are glad you’ve been thinking about the cool science of a barometer! Barometers are measured by inches in mercury, and the units are measuring barometric pressure! :)

      • I had to watch the video to find out when I asked plus I probably am older than you so it was better I joke of course

        • Hey there, Wounder Friend F! We are glad you learned something new from our Wonder video today! HOORAY for you! :)

  2. Well I saw it. It was so coo I could not stop smiling!!!!!! ( I LOOKED LIKE THHIS ————> :D )

    • Well that sure is spectacular, isn’t it, Wounder Friend F?! We love to smile, too, it makes us very happy. We smile when we laugh, when we are excited, and even when we’re surprised! Isn’t it cool to think about all the different ways we express our emotions, Wonder Friend? :)

    • Welcome back to Wonderopolis, Wounder Friend F! :) Have you heard the saying “actions speak louder than words?” Sometimes we do means more than what we say. We can say kind things, and we can show kindness through a hug. Perhaps you can talk to your family or teacher about body language. How can you show kindness through words and actions? :)

    • We are SO happy that you liked this Wonder! Come back and hang out with us anytime, Wonder Friend F! Talk to you again soon! :)

    • Hey there, Wounder Friend F! We love your comment, and we look forward to WWYL (WONDERing with you Later)! :)

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Have you ever wondered…

  • What does a barometer measure?
  • How much pressure does the atmosphere exert on you at all times?
  • How do changes in air pressure signal changes in the weather?

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Try It Out

How’s the weather? Gather together a few friends or family members to check out one or more of the following fun activities:

  • How accurate is the weatherman where you live? Keep track and find out! Over the course of the next week, watch the weather report at the same time each day. Take notes in a journal. Make sure to record predictions for temperature and precipitation. Then make careful observations about the weather on your own. Did the weatherman get it right? How often? Would you like to be a weather forecaster one day? Why or why not?
  • Are you ready to predict the weather? You can be a weather forecaster in the making when you Build Your Own Barometer with just a few simple supplies. Be sure to ask an adult for help. Once you have built your barometer, put it to the test. Can you track changes in atmospheric pressure? Do they predict changes in the weather? Do you think your barometer is accurate? Why or why not?
  • Air pressure can be a hard scientific concept to grasp. After all, air is invisible, which means it’s not the easiest thing to observe! Can you see air? If it’s really windy outside, you might see the effects of wind, but can you see the wind itself? Not really! Air pressure is the same way. Science tells us that it’s always pushing down on us, but it’s hard to observe. To see air pressure in action for yourself, you can show your friends and family the amazing power of air pressure with this super-cool Unspillable Water Experiment!

Still Wondering

Visit Science NetLinks’ Properties of Air lesson to learn more about how air takes up space and puts pressure on everything around it.

 

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