Air Pressure Curriculum

Section 2—Lesson 4: Considering How Well Models Depict Air Pressure as Omnidirectional

Background Information

Air Pressure as Omnidirectional Rather Than Unidirectional

In order to understand air pressure as scientists do, students need to think about air pressure as something that exists all around them and behaves in an omnidirectional manner. However, the language and models that we use can inadvertently reinforce a unidirectional model. People often use the terms "force" and "pressure" interchangeably, even though they represent two different things. Air pressure is a scalar quantity. In physics, this means that it can be specified by its magnitude or size without paying any attention to direction. On the other hand, force is a directional quantity. In order to describe it completely, you need to specify both its magnitude and its direction.

Explain that part of the problem that students have in visualizing air pressure, which leads them to see it as forceful (having a direction), has to do with thinking about the individual molecules that make up the air versus the effect of all the molecules together. While each individual molecule DOES have a force and therefore a direction, air pressure is all of them together bouncing around, which results in omnidirectional pushing, not a push in a certain direction.

Models That Reinforce Erroneous, Force-like Conceptions

Students (and many textbooks) often use arrows to represent air pressure in models that they draw. If students depict a book on a table, their models typically show arrows pointing downward towards the book. They think of air pressure "pushing down" on the book, like a force, rather than envisioning the individual molecules colliding and bouncing off the book in all directions equally—a collective behavior which results in air pressure. If students depict a balloon in the air, their models typically show arrows pointing towards the balloon in all directions. Although more accurate than a unidirectional model, this model still shows that students think of air pressure actively pushing in on objects, like a force, rather than air pressure as existing in a passive sense.

In this lesson, students compare models depicting air pressure, and determine which model best conveys the omnidirectional and passive nature of air pressure.