Hands-on Activity: Air Pressure
Educational Standards :
Learning Objectives (Return to Contents)
After this activity, students should be able to:
Materials List (Return to Contents)
Each student needs:
Introduction/Motivation (Return to Contents)
Ask the students if they notice the pressure on their ears when they dive to the bottom of a swimming pool. The pressure in a pool increases with depth just as air pressure increases as you go deeper into the sea of air (atmosphere). The bottom of the sea of air is represented by sea level while higher elevations represent shallower parts of the atmosphere. As you move to shallower parts of the atmosphere, such as the top of Mount Everest, the pressure decreases.
Pressure is measured in different units. Scientists and engineers typically use the metric unit Pascal (Pa). A Pascal is defined as the pressure exerted by 1 Newton weight (1 kg under the Earth's force of gravity) resting on an area of 1 square meter. Below is a list of some of the common units used to measure pressure and their equivalents. Please note that many additional units exist for pressure.
At sea level, the atmospheric air pressure can be represented as any of the following: (Write the units on the board.)
Procedure (Return to Contents)
Pressure (P) is defined as the amount of force (F) applied per unit area (A) or as the ratio of force to area:
P= F/A (equation 1)
The pressure an object exerts can be calculated if its weight (the force of gravity on an object) and the contact surface area are known. For a given force (or weight), the pressure it applies increases as the contact area decreases. (To better understand this, hold a large book flat on your outstretched hand and notice how much pressure the book puts on it. Next, try to balance the book on the tip of your index finger. How much pressure does it seem to exert now?) It is also important to note that air pressure decreases with increasing altitude. It is helpful to think of the atmosphere as a swimming pool, with the water representing the air.
Before the Activity
With the Students
What happens every time the sides of the square are increased by 1 inch? (Answer: This is harder since the relationship is not linear. Every time you increase the length of the sides by one inch the force increases by more than 12 lbs. In fact, as the length of each side gets longer the increase in the force gets larger as well. When the length of the sides are 1 inch, the force is 12 lbs. If we increase the sides to 2 inches, the force becomes 48 lbs. This is an increase of 36 lbs. If we add another inch and make each side 3 inches, the force becomes 108 lbs, which is an increase of 60 lbs. If we plot the length of each side vs. the force, we see that the relationship is not linear. The line curves up, which is known as an exponential relationship.)
Attachments (Return to Contents)
Assessment (Return to Contents)
Discussion Question: Solicit, integrate and summarize student responses.
Activity Embedded Assessment
Worksheet: Have students record measurements and follow along with the activity on their worksheets. After students have finished their worksheets, have them compare answers with their peers.
Graphing: Have students use the information from their worksheets to create line graphs of the relationship between area and force. Plot area (in2) on the x-axis and force (ponds) on the y axis. Ask students or teams to explain what is happening in their graphs in their own words.
Activity Extensions (Return to Contents)
Have students complete an Air Pressure Worksheet for planets where the air pressure is different than on Earth. Examples are Jupiter (735,000,000 psi), Venus (1,325 psi), Mars (0.25 psi), Pluto (0.000147 psi). Have students discuss what kinds of challenges these pressures might impose on manned and unmanned missions to these planets.
Activity Scaling (Return to Contents)
For older students:
References (Return to Contents)
ContributorsTom Rutkowski, Alex Conner, Geoffrey Hill, Malinda Schaefer Zarske, Janet Yowell
Copyright© 2004 by Regents of the University of Colorado.
Supporting Program (Return to Contents)Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
Acknowledgements (Return to Contents)
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.