1. Air Pressure

2. Even thought air is invisible, it is made of molecules: 78% Nitrogen 21% Oxygen 1% Carbon Dioxide, Water vapor, Argon, and other gases. http://ed.ted.com/lessons/how- heavy-is-air-dan-quinn#watch

3. Four facts about air:  Why? 1. Air takes up space! Tape a balled up paper towel on the bottom of a cup. Next, submerge the cup upside down in a bowl of water. What happens to the paper towel? The paper towel stays dry! The air trapped in the cup takes up space – it won’t allow the water to rise into the cup!

4. Four facts about air:  Why? 1. Air has weight! Balance a meterstick with a balloon on either end. Remove one balloon and blow it up, then tie it closed. Put it back on the same spoton the meterstick. Is the meterstick still balanced? No!! Adding air to the balloon addes weight, so the meterstick is no longer balanced!

5. Four facts about air: 1. Air exerts pressure! Imagine a pile of books stacked one on top of the other. The pressure on the bottom is much greater than on the top. Would you expect air pressure to be higher at sea level (the bottom), or on a mountain (the top)? On the bottom! Pressure at sea level is about 15 lbs/in²

6. The pressure in the atmosphere is called Barometric Pressure. We measure it using a barometer.

7. Four facts about air:  Why? 1. Hot air takes up more space than cold air! Stretch a balloon over the top of a 2L bottle. Place the bottle in a bowl of very hot water. What happens to the balloon? It will inflate! The air in the bottle warms up and expands, pushing into the balloon!

8. Bernoulli’s Principle:  Why? As the speed of a moving fluid (like air) increases, the pressure decreases. This means that the faster the wind is blowing, the lower the air pressure is. What happens when I blow between the cans? They roll together! When the air between the cans is moving, the pressure is lower, and the pressure on the other side presses them together.