Feeling The Pressure

SCIENCE CONCEPT:

Since air has weight, it is held to the earth by the force of gravity, just as you are. Since gravity is strongest near the earth's surface, it holds most of the air, or atmosphere close to the earth's surface. This pushing force of the air is called air pressure, and the closer to the earth you are, the stronger the air pressure.

STUDENT OBJECTIVE:

The student will explore air pressure using a drinking straw experiment and how gravity exerts its greatest strength near the earth's surface.

OVERVIEW:

In this activity, students will discover how gravity exerts its greatest strength at the earth's surface over air pressure. In the drinking straw experiment, the student will put a straw in a glass of water and then suck some water up into the straw. Then the student will quickly cover the top of the straw with their finger and lift the straw out of the glass. Does anything happen? No? Then have the student lift their finger off the top of the straw. Now the air can get into the top of the straw and the water can flow out because of gravity.

PREPARATION TIME:

5 minutes.

LESSON TIME:

15 - 20 minutes.

TEACHER PREP:

Gather materials that are needed for the experiment. You will need a drinking straw, a glass, and water.

WORDS TO KNOW:

air pressure

weight

gravity

atmosphere

force

TEACHER TEXT:

Talk to anyone interested in science and chances are they will remember how the drinking straw experiment demonstrates how air pressure works right in your kitchen. Because gravity is greatest closest to the earth's surface, the straw experiment works best on the earth's surface. The higher you go in altitude, the less air pressure there is. When the astronauts are on the space shuttle there is no gravity so the astronauts cannot suck water up a regular straw. Astronauts have special straws with a clamp on it because there is no gravity to hold the water in the straw by air pressure.

Air pressure can be felt in so many ways. Stand outside on a really windy day and you will feel the air pressure trying to knock you over. When you ride your bike down a hill you can feel the air pressure in your face or when you ride in a car and open the window you can feel the wind in your hair. Air pressure is all around you. Blow up a balloon and secure the end in a knot. Release it and watch it being tossed around by air currents and air pressure. Intense air pressure is present when there is a hurricane or tornado. Because air has weight we are "weighted" by the amount of gravity pushing against our mass.

In outerspace, because there is no gravity, we become weightless. Astronauts experience different things because of this weightlessness - floating in air, being able to bounce along like a kangaroo when 'walking', needing special instruments to eat, 'take showers' and go to the bathroom. That is why the straw in outerspace is designed differently than the straw you will find in your own kitchen.

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Last modified: Sat Dec 13 15:35:22 PST 1997