Air Pressure Curriculum

Section 1—Lesson 2: When Non-obvious Causes Become Obvious

Background Information

Inferring the Existence of Non-obvious Variables Through Obvious Changes in Effects

Sometimes we observe obvious effects that correspond with changes in other variables (even if those variables are typically non-obvious). This can lead us to question whether there are other, as yet undetected, variables that play a role in the outcome. For instance, regular fluctuations in the liquid inside the barometer tube suggest that some variable is responsible. If we find that changes in air pressure correlate with certain outcomes in a predictable way, such as the movement of a liquid in a tube, air pressure may be involved in the movement of the liquid. (It does NOT mean that there is definitely a causal connection; rather that there is a correlation to be investigated further.)

To introduce the variable of air pressure and to make air pressure around us obvious, in this lesson, students consider the barometers (although they are not named as such) that they created in the last lesson. A barometer is an instrument used by meteorologists to measure changes in atmospheric pressure. These changes are most obvious during times of inclement weather, when weather fronts move into or out of an area. This activity works best if there is a period of fluctuating weather during the time span when students are observing their barometers.

Note to Teacher: This lesson formally introduces the concept of air pressure. It assumes that students already understand that pressure is the force per unit of surface area, where the force is applied perpendicularly to the surface area (Pressure = Force/Area). If they do not, you may want to teach it first. (Activities such as the "bed of nails" where someone, usually the teacher, lies down on a bed of nails, can effectively illustrate the relationship between force, area, and pressure. Students are asked to apply this understanding to air pressure, which is the collective result of the molecules that make up the air applying forces against any surface with which they have contact.)