Air Pressure
- What is Air Pressure?
- Differences in Air Pressure
- Measuring Air Pressure

When you take off or land in an aircraft, your ears may hurt or feel uncomfortable. This is because your eardrums can feel changes in air pressure as the aircraft moves quickly up and down. But what is air pressure?

What is air pressure?

It is caused by the weight of all the air in the atmosphere pressing down on Earth. It is also known as atmospheric pressure. Air pressure changes with the height and also when air warms up or cools down (temperature). Changes in air pressure cause changes in weather.

Feel the effect of air pressure.

Differences in air pressure

When air rises, it leaves behind an area of lower pressure, because the upward- moving air is not pressing down so hard on the surface. Areas of high pressure are formed where air is sinking back down, and so pushing down harder. >> A diagram shows differences in air pressure.

There are many areas of high and low pressure above the Earth's surface due to uneven surface heating. Air moves from areas of high pressure to low pressure, forming winds. As a result, the greater the difference between the high pressure and low pressure areas is, the higher the wind speed is.

Highs and lows?

Pressure is different all over the world. Lows are areas of low pressure with the lowest pressure at the center. Highs are areas of high pressure with the highest pressure at the center. The way these move from day to day causes the changes in the weather. Lows usually bring wet, cloudy weather. Highs bring sunnier,dry weather.

Measuring Air Pressure

Measuring Air Pressure

Measuring air pressure Air pressure is measured in millibars (mb) on a barometer. The simplest kind of barometer is a mercury barometer and pressure is measured in mm (in) of mercury. An aneroid barometer can measure air pressure more conveniently. A barograph is a special kind of barometer. It records continuous changes in air pressure.

>> This a diagram which shows how a mercury barometer works.

How to make a barometer ?

>> A Barograph
>> An Aneroid Barometer

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