Air Pressure

Air (barometric) Pressure The weight of air pressing down on Earth. Air Pressure can change from place to place, and this causes air to move, flowing from areas of high pressure toward areas of low pressure. It’s the same as barometric pressure.

Density The measure of how tightly packed the matter in an object is (hot air and low pressure= less dense; cool air and high pressure= more dense)

High Pressure System A whirling mass of cool, dry air. Because cool air is heavy and denser than warm air, it sinks. High pressure brings fair weather, sunny skies, light winds, and stable weather. High pressure systems rotate clockwise.

High Pressure System The air moving away from the High pressure system leaves a "hole" to be filled, so air from above sinks into that "hole". As the air sinks, water that was in the condensed form (like clouds) tends to evaporate into water vapor. This means the water is not in the condensed form needed to make clouds and precipitation. That's why many people see a H on a weather chart and know good weather and clear skies are coming!

Low Pressure Systems A whirling mass or warm, moist air. Because warm air is lighter and less dense than cool air, it rises, and then cooler air flows in underneath. Low pressure systems bring storms, strong winds, and changing, unstable weather, low pressure systems rotate counter-clockwise.

Low Pressure System Air moves into a Low pressure system. It pushes any air that was there up. As the air rises, water vapor condenses into clouds that can bring precipitation. That's why many people see a L on weather chart and know there is a good chance of "bad" weather - cloudy skies and possibilities of rain or snow.

Oh! The Pressure! We live at the bottom of and “ocean of air” called the atmosphere. This ocean is about 350 miles deep. Most of the weather you experience takes place in the bottom 3 miles of this ocean.

Did You Know… Air pressure changes a lot as you go up in elevation. But, air pressure can change right here on the ground. Usually changes in air pressure happen too slowly for most people to feel. You probably have noticed something that a change in air pressure causes- WIND!

Our Experiment! We are going to observe what happens to the air in a bottle when we submerse it in a tub of cold water and a tub of hot water. Put the balloon over the mouth of a bottle. Put the bottom of the bottle into the warm water first. What happens? Put the bottom of the bottle into the cold water. What happens?

Create! Create a five-cornered star on the next available sheet in your science notebook. Don’t waste paper! Use fronts and backs! Like this: Conclusion/ Why did it happen? Problem/Focus Questions Results/What happened? Hypothesis Materials/ Procedures 11/12/2018

Step #1 Problem/ Focus Questions What happens to molecules in air when air is heated? What happens to molecules in air when air is cooled? What does this have to do with weather? 11/12/2018

Step #2 Materials/Procedure Add the materials/procedures to your star second! Here’s what you’re going to do: Place the balloon gently over the lip of the bottle. Place the bottle into a pan of hot water and observe what happens. Place the bottle into a pan of cold water and observe. 11/12/2018

Step #3 Hypothesis What do you think will happen when you place the bottle in the hot water? What do you think will happen when you place the bottle in the cold water? 11/12/2018

Step #4 Results/What happened? In the “Results” section of your star, tell what you saw! Create a diagram that shows what you saw, too! 11/12/2018

Step #5 Conclusion/Why did it happen? Was your hypothesis correct? Answer the focus questions! 11/12/2018

Video – Explanation www.discoveryeducation.com Watch the video at the link below for more information about what happens when air is heated. You can change your conclusion based on this new information, if you like. http://player.discoveryeducation.com/index.cfm?guidAssetId=9760A447-0E1F-4E72-9C36-0C2897A108A8&blnFromSearch=1&productcode=DSCE 11/12/2018

Think about this… What happened? Why did the balloon Inflate when dipped in the warm water? Why did the balloon Deflate when dipped in the cold water? What does this tell us about air pressure and how it works?