Atmospheric pressure

The air has weight. It pushes on everything. This push is called air pressure.

Air pressure is strong at the beach. This is because there is much air above you.

Air pressure is weak on a tall mountain. There is less air above you there.

High pressure and low pressure change the weather. Big storms can have very low pressure.

Air pressure even changes how water boils. It is a busy part of our world.

Air has weight. This weight pushes on everything it touches. We call this air pressure.

Earth's gravity pulls on the air above us. This pull makes the air press down. At sea level, the pressure is high. This is because there is a lot of air above you.

As you go higher, the pressure drops. There is less air above you on a mountain.

Pressure changes can cause big weather events. A tropical cyclone is a large storm. These storms have very low pressure in their center.

Air pressure also changes how things boil. Pure water boils at 100°C at sea level. If the pressure is lower, water boils at a lower temperature. This is why cooking on high mountains is different. Scientists use a tool called a barometer to measure pressure. Pilots use a tool called an altimeter to help fly planes.

Atmospheric pressure is the weight of the air pressing down on everything. It is also called air pressure or barometric pressure.

This pressure is caused by Earth's gravity pulling on gases. Gravity holds the atmosphere close to our planet. The amount of pressure depends on how much gas is above you. At sea level, the pressure is quite high. Scientists use a unit called an atmosphere, or atm, to describe this. One atm is about 1,013.25 millibars.

How does this pressure work? Think of it as a tall column of air sitting on your head. At sea level, that column is very heavy. As you climb a mountain, the column becomes shorter. This means there is less air mass above you. Because there is less weight, the pressure goes down. Temperature and humidity also change the pressure. Pressure is higher when it is cold and lower when it is humid. This step-by-step change helps us understand our weather.

People have used pressure to learn about our world for a long time. In 1774, Nevil Maskelyne worked on a mountain in Scotland. He wanted to test a theory about gravity. He used pressure to measure how high the mountain was.

Another man named William Roy helped him. Roy used a tool called a barometer to check the heights. Their measurements were very close, within one meter. This helped people make better maps of the land.

There are many amazing records for air pressure. The highest pressure ever recorded was in Siberia. This area is known for the Siberian High. The lowest pressure happens in the middle of big storms. These include tornadoes and tropical cyclones.

A record low was set during Typhoon Tip in 1979. In the western Pacific Ocean, a plane measured this very low pressure. On the other hand, the Dead Sea is very low in the land. Because it is below sea level, the pressure there is very high.

Pressure affects many things you see every day. It even changes how water boils. At sea level, pure water boils at 100°C.

If you are high on a mountain, the pressure is lower. This means water boils at a lower temperature. Pilots must also watch pressure to fly safely. They use an altimeter to adjust for the air. This tool helps them know how high they are in the sky.

Atmospheric pressure is the force exerted by the weight of the air in Earth's atmosphere. It is also known as air pressure or barometric pressure. This pressure is a vital part of our planet's weather and climate systems.

Scientists often use a standard unit called an atmosphere, or atm. One standard atmosphere is defined as 1,013.25 millibars. This is also equal to 760 torr or about 14.696 pounds per square inch (psi). This value represents the average pressure found at mean sea level.

The mechanism behind this pressure is the gravitational attraction of the planet. Gravity pulls on the various atmospheric gases, holding them close to the Earth. The total pressure is a function of the planet's mass and its radius. It also depends on the amount and composition of the gases. The vertical distribution of these gases determines how much weight sits above a specific point. This pressure is often described as hydrostatic pressure. This means it is caused by the weight of the air column above a measurement point.

Atmospheric pressure changes significantly based on altitude. As you move higher away from the Earth's surface, the pressure decreases. This happens because there is less overlying atmospheric mass above you. At low altitudes, the pressure drops by about 12 pascals for every 100 meters. The pressure varies smoothly from the surface to the top of the mesosphere.

Temperature and humidity also play a role in these changes. Pressure is proportional to temperature and is inversely related to humidity. This means that as humidity increases, the pressure tends to decrease.

There are different ways to measure and report pressure depending on the location. Mean sea-level pressure (MSLP) is the pressure at mean sea level. Meteorologists use this value in weather reports on television and the internet. In aviation, pilots use an altimeter setting to adjust for pressure. This helps them determine their height accurately. In the United States and Canada, this is often reported in inches of mercury. Other regions use hectopascals (hPa) or millibars. One hectopascal is exactly equal to one millibar.

History shows us how pressure measurements helped science grow. In 1774, Nevil Maskelyne used pressure to test Newton's theory of gravitation. He conducted the Schiehallion experiment on a mountain in Scotland. He needed to measure the mountain's elevation accurately for his work. William Roy also used barometric pressure to confirm these height measurements. Their results were incredibly close, with an agreement within one meter. This successful use of pressure tools became vital for survey work and map making.

Extreme pressure records show the power of Earth's weather. The highest sea-level pressure occurs in Siberia during the Siberian High. This can reach levels above 1,080 hPa. The lowest measurable pressures are found in the centers of tornadoes and tropical cyclones. A record low was set in 1979 during Typhoon Tip in the western Pacific. An aircraft measured this extremely low pressure from the air.

Conversely, the Dead Sea is a very low point on land. Because it is 430 meters below sea level, it has a high typical pressure of 1,065 hPa.

Atmospheric pressure even affects the physical properties of liquids. For example, it changes the boiling point of water. Pure water boils at 100°C at standard atmospheric pressure.

However, the boiling point is the temperature where vapor pressure equals atmospheric pressure. At lower pressures, such as on a high mountain, water boils at a lower temperature. This is why cooks must adjust recipes at high altitudes. In science, a vacuum pump can lower the pressure to evaporate liquids at lower temperatures. This connects the study of air pressure to the study of thermodynamics and chemistry.