EQ: What is air? Classroom Unsquared

Air is a mixture of gases held around the Earth by the pull of gravity. The gases are about 78% Nitrogen 21% Oxygen 1% other gases like Carbon Dioxide Water Vapor - amount changes

Let’s do a few experiments to observe a property of air. A toilet plunger will stick to a whiteboard when it is pressed on. Why? ep/i3b92d18aa7a6/67f8a959897e.jpg Fill a jar with water over a sink, place a notecard over the entire opening, flip it upside down, and carefully release the card. The card holds the water in! What? WEAR SAFETY GLASSES PLEASE !

Put some water in a jar. Fill a test tube with water. Quickly flip the test tube upside down into the water. Whoa! Why doesn’t all of the water drain out? Put about ½ inch of water in empty soft drink can. Heat on hot plate until water boils for a minute. Grip can with tongs and flip it quickly upside down into ice water. Why does the can crush? HOT PLATE AND CAN ARE HOT! Wear goggles!

So what do all of these experiments have in common? Air seems to be able to push on things. Where was air pushing to make those events? The gases in the air are very small particles, visible only to the most powerful microscope. The particles are called atoms or connected atoms called molecules, like in this diagram. They are free to move around in their container, and they do at high speeds. They collide with the sides of the container by the millions and put a force on each inch. This is called air pressure.

Air pressure pushed down on the outside of the plunger, … Pushed up on the outside of the notecard, … Pushed in on the soda can when the steam cooled into liquid water, … And pushed down on the water surface holding the tube water up!

Let’s think about the test tube experiment. If the outside room air pressure goes up, the water line in the tube will go up. If the room air pressure goes down, then the water level will go down! Why? About 30 in. Mercury We can use the tube and dish to measure air pressure! It is called a barometer. Meteorologists use mercury instead of water because it’s heavier so the height is lower, about 30 inches normally. Watch it work…

The layer of air around our Earth is called the Atmosphere. If the Earth was the size of a basketball, it would be a layer 1/16 th of an inch thick! The Atmosphere acts like a “swimming pool” of air 75% of the gases are in the Troposphere (bottom layer) All weather occurs in the troposphere On the graph, air pressure is measured in millibars (mb). 1000mb is about 30 inches, normal air pressure at sea level.