Use your Air Pressure Guide Notes with these slides. Barometric Pressure. B ar ometric Pressure. i. What is barometric pressure?. The air is made up of molecules. . Air molecules are all around us. kg. Like all matter, air molecules have mass.
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Use your Air Pressure Guide Notes with these slides.
What is barometric pressure?
The air is made up of molecules.
Air molecules are all around us
Like all matter, air molecules have mass.
Gravity pulls the air molecules toward the earth, giving them weight. The weight of the air molecules all around us is called the air pressure.
Weather changes as air pressure changes.
Three factors change air pressure in the atmosphere. Stay alert to learn what they are.
Now answer #3 and #4. Why does Earth have a blanket of air on the outside? Why doesn’t the moon have an atmosphere?
(Psst! The arrows are a hint.)
Air pressure (fluid pressure) is from all directions, not just downward.
Pressure = force per unit area
Air pressure at sea level is ~ 14.7 lbs/ in2
Barometric pressure goes down.
As elevation goes up
What makes air pressure change?
This is an inverse relationship.
We can graph it!
High altitudes = lower pressure
Low altitudes = higher pressure.... See?
#11, 12, 13 Check:
#15: Since pressure changes with altitude…
…how does changing altitude affect a barometer?
Air inside a ball pushes against the sides.
The more air we put in a ball, the more the molecules push.
So the pressure increases as we add air.
What makes air pressure change?
But what about this?
Does pressure lower when the ball gets hotter?
= increasing air pressure.
A falling barometer = decreasing air pressure.
This usually means wet weather.
(Does the barometer really fall?)
I have an umbrella and you don’t.
to measure air pressure.
How can I represent the downward force of air?
In 1643, Evangelista Torricelli invented the barometer
Torricelli’s barometer used a glass column suspended in a bowl of mercury. The pressure of the air molecules pushed the mercury up into the glass tube.
The weight of the mercury in the tube was equal to the weight of the air pressing down on the mercury in the dish.
As atmospheric pressure increases…
The mercury in the tube rises.
That’s why it is called a mercury barometer. (#22)
The Mercury Barometer
Is there a better way to measure air pressure?
The Aneroid Barometer!!
Get yours today!!
An aneroid barometer uses a cell which has had most of the air removed (hence the name).
As the air pressure around the cell increases, it presses on the cell, which causes the needle to move.
Television weather forecasters usually give barometric pressure in inches of mercury. However, meteorologists measure atmospheric pressure in millibars or bars.
#25 Two types of barometric pressure measurements:
Station pressure is the actual pressure at the recording location. It is affected by the local altitude.
Sea level pressure is referenced to sea level, so it has the same altitude anywhere in the world.
Most aneroid barometers have a needle which can be set to remember the previous reading.
#26 Why would this be important?