# Pushing Down

Have you ever tried to touch the bottom of the swimming pool in the deepest spot? You might have noticed that the deeper you went your ears felt funny or even hurt. Also, it was difficult to hold your breath for long under the water.

Now imagine that you dive to the bottom of the ocean. The pressure of the ocean water above you is so heavy that you cannot survive. The air above us isn't as heavy as water, but it does put pressure on our bodies. (Sometimes your ears "pop" because of the change in air pressure when we travel in a car or plane.)

Since air is a substance, something that takes up space, we can observe the effect it has on us and the things around us.

How can air be a substance? You really can’t see it. Here is an experiment to prove it! You will need these materials: one string 24 inches long , meterstick(or yardstick), two strings 6-inches long , 2 flat balloons

 Tie a 24-inch piece of string around the middle of a meterstick or yardstick. This is a handle. Tie a 6-inch piece of string on each flat balloon. (Don't blow the balloons up.) Tape a flat balloon to each end of the stick. Move the handle-string until the stick balances. Write down where your handle-string is located (the number on the stick). Remove one balloon and blow it up. Tape it back onto the stick. Move the handle-string until the stick balances. Write down where the handle-string is now tied. What happened? Explain how this activity demonstrates that air is a substance.

Extension: Create a different experiment that demonstrates air is a substance?

Air moves differently as its temperature changes. Warm air rises, and cool air sinks. This creates wind.

The chart below was developed by Sir Francis Beaufort of England in 1805. It illustrated various wind speeds. It was modified from the NOAA Beaufort Wind Scale.

 Observation Estimated Wind Speed Smoke drifts with air 1-3 mph Wind can be felt; leaves rustle 4-7 mph Leaves and small twigs move; flags move 8-12 mph Small branches sway; dust and paper blow 13-18 mph Small trees sway 19-24 mph Large branches sway 25-31 mph Whole trees sway; walking is difficult 32-38 mph

Your challenge is to use the Beaufort Wind Scale to determine the wind speed on four different days or at four separate times of one day. Record your data in a chart similar to the one below.

 Date Time Observation Estimated Wind Speed

Download the plug-ins: , and . (The QuickTime plug-in is needed to play sounds and movies correctly.)

Want to share photos of you or your friends doing this activity? Send it in an e-mail with the following information:

1. The title of the activity