Today’s Wonder of the Day was inspired by emma. emma Wonders, “What does a barometer measure?” Thanks for WONDERing with us, emma!

Can you feel the pressure? It’s there. All the time. Everywhere you go. What is it? Atmospheric pressure — often referred to simply as air pressure — is the constant force on your body by the mass of air particles.

You can’t see these tiny air molecules, 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 climb a mountain, for example, the air pressure will be lower. Why? The length of that air column above you has decreased with your increase in altitude.

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 may also need to breathe faster to take in more oxygen molecules to make up for the deficit.

Air molecules also take up space. Because there is a lot of 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 under high pressure.

Earth’s atmosphere presses down on you with a force of almost 15 pounds per square inch. You may WONDER 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 often, you may hear weather people talk about barometric pressure. Forecasters use a special tool called a barometer. It measures 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). Changes in air pressure, as measured with barometers, predicts 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 people monitor air pressure, falling barometer readings can signal that bad weather is on the way. In general, if a low pressure system is coming, be prepared for warmer weather with storms and rain. If a high pressure system is near, you can expect clear skies and cooler temperatures. 

Do you like to watch the weather? How can knowing what the weather might be like help you in planning your day?

Standards: CCRA.R.1, CCRA.R.10, CCRA.L.3, CCRA.L.4, CCRA.L.5, CCRA.L.6, SMP.5, SMP.6, NGSS.ESS1-2, NGSS.ESS3-1, NGSS.PS2-1

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If you like candy or soda, tomorrow’s Wonder of the Day will be a nice change of pace!