1. Air Pressure

2. Air is a mixture of atoms of different gasses. Because it is made of atoms, it has mass and it takes up space. Because it has mass and takes up space, it is considered matter. Matter of any kind has properties. Two important properties of air as matter that are related to each other and have a direct impact on weather are density and pressure. Air is Matter

3. Density is a property of matter that measures how much matter there is in a specific amount of space. The density of air measures the quantity of gas molecules that are together in one area of volume. Density is calculated as mass volume. Air density More Dense Less Dense

4. The earth’s gravity pulls air particles towards it. Because of this, there are more molecules of air gasses closer to the surface. Air density Therefore, the lower the elevation (or the closer to the surface at sea level), the greater the density; while the greater the elevation, the lesser the density.

5. Air is said to be “thinner” in mountain elevations because it is less dense. Air density Even though the air is less dense, the ratio of the gasses remains (78% N 2, 21% O 2, and 1% other gasses) - no matter how high the altitude is. N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2 N2N2N2N2 O2O2O2O2

6. Since air is matter, it has weight that pushes on everything it touches - just like how your weight is pushing on the seat right now. The force of air pushing on an area or a surface is called air pressure. To experience pressure, think about wearing a backpack on your shoulders with all your books in it. The matter in the backpack is pulled by gravity giving it weight, which causes pressure to be exerted on your shoulders. Air Pressure

7. The density of the air directly contributes to how much air pressure there is. Air pressure More dense air has more matter and therefore has greater air pressure.

8. More dense air has more pressure Less dense air has less pressure Air pressure

9. Air in lower altitudes has greater pressure for two reasons: Air pressure 1.The air is more dense. 2.There is more weight to the air because there is all of the matter of air above it.

10. Imagine the stack of objects to the right. How does the matter of each object compare? Now imagine placing your hand in between the various objects. How does the pressure your hand feels change? Air pressure

11. The air pressure pushing down on your desk is as much as the weight of a large school bus. Air pressure However, the air pressure being exerted on your desk is coming from all directions which keeps the desk from breaking. The amount of pressure pushing down on it is the same as the amount pushing up from underneath.

12. Reading and measuring air pressure levels serves as an indicator to certain weather conditions. High pressure air is associated with comfortable and dry weather conditions; while low pressure air is associated with poor and wet weather conditions. Air pressure is measured with a barometer. Barometers

13. Since low air pressure is less dense air, there is more space in between the particles. This space becomes filled with water vapor. Low pressure is therefore associated with bad weather – too much water vapor in the air will eventually cause it to rain or be stormy. In weather forecasting, if the measurements of a barometer indicate that pressure is dropping, it is safe to assume that bad weather is approaching. Barometers

14. High Pressure High Density Less room for water vapor BETTER WEATHER Barometers Low Pressure Low Density More room for water vapor WORSE WEATHER

15. Barometers read the air pressure by adjusting to how hard the air pressure around it is pushing. High pressure air pushes harder on the barometer, causing the measurement to be a higher number. Compare it to the game. The more pressure exerted by the hammer, the higher the number it registers. Air pressure pushes a barometer in the same way. Barometers

16. Barometer measurements are either given in inches or millibars, depending on the type of barometer that is being used. Normal air pressure is approximately either 1,016 millibars or 30 inches (aneroid barometer) (mercury barometer) Barometers