The Problem With Air Pressure

Air pressure is one of those topics that students nominally know something about from everyday life and have almost always misconceived. The documented misconceptions are a long list: air is “empty” (nothing in it), air is weightless, air only exerts pressure when it moves (like wind), a vacuum “sucks” rather than being a region where surrounding air pushes in, and pressure increases with height rather than decreasing.

Some of these misconceptions are stubborn precisely because everyday experience seems to support them. Air does not feel like it has weight. A vacuum cleaner does feel like it is pulling. The atmosphere, experienced from inside it, does not announce itself as a pressure source.

The standard approach to this material — explaining atmospheric pressure, defining $p = F/A$, working through barometric altitude formulae — addresses the conceptual gaps at the declarative level. Students can recite that air exerts pressure in all directions. Whether they have actually updated their mental model is a different question.

“Mission to Mars” is a design-based attempt at conceptual change through physical encounter with the consequences of pressure differences.

The Context: Why Mars?

The motivation for choosing the Mars context was empirical, not poetic. The ROSE study — a large international survey of student interests in science — consistently finds that space, astronomy, and human exploration rank among the most motivating contexts for physics learning, for both boys and girls. Physics education research in Germany has known for decades that generic “physics” lessons underperform motivationally compared with context-embedded physics, and astronomy is one of the contexts with the clearest evidence base.

“Mission to Mars” asks students: a crewed mission to Mars would travel through the vacuum of space, with the crew living in a pressurised compartment. The compartment has to maintain atmospheric pressure while surrounded by near-vacuum. What happens if it fails? And how would you design a spacecraft structure to prevent that failure?

The question is concrete. The physics behind it — the difference between the pressure inside the compartment and the near-zero pressure outside, and the forces this pressure difference exerts on any structure — is the content of the lesson.

The Experiment

The full version of the experiment, as we ran it at the astro-lab at the University of Cologne, uses a vacuum pump, a bell jar, and a smartphone running phyphox. The smartphone’s built-in barometric pressure sensor records real-time atmospheric pressure inside the bell jar as the pump evacuates it.

Before building anything, students verify that the smartphone is a functional pressure gauge: they measure the current atmospheric pressure in the room and compare it with a provided reference value. This step matters pedagogically — it establishes that the phone is a real scientific instrument, not just a device for receiving worksheets.

Then comes the design-build-test cycle:

Design: Students are given PVC plumbing pipe sections, empty food containers, resealable bags, rubber bands, clamps, and other household materials. Their task is to build a prototype “spaceship” — a container that will maintain near-atmospheric pressure inside while the bell jar around it is evacuated to low pressure. The phone (or external sensor) goes inside the prototype to measure whether the prototype is holding.

Predict: Before testing, students are asked to state why they think their prototype will or won’t work. This surfaces their preconceptions in a low-stakes way and sets up the next stage.

Test: The prototype goes into the bell jar. The pump runs. The pressure sensor records. The light curve — sorry, the pressure curve — tells the story. Four outcomes are possible:

• Nearly flat line: the prototype is airtight, pressure inside stays near atmospheric. Mission success.
• “Bathtub” curve: a visible failure event — a cap pops off, the pressure inside drops sharply and then equalises. Students hear the pop. They did not expect the pop. This is the moment.
• Gradual decay: the prototype leaks slowly, the pressure inside drops steadily. Invisible failure.
• Noisy signal: something wrong with the setup.

The PVC pipe trap: the PVC pipe is deliberately included because it is the most impressive-looking material and is reliably incorrect. The friction between pipe and lid is insufficient at the pressure differences reached in the bell jar. The lid pops off. Students rebuild.

The Misconceptions, Addressed

The design-test-rebuild cycle forces students to confront the misconceptions listed above in a direct physical way:

Air is empty/weightless: handled in pre-activities with standard demonstrations (the dunked napkin, the deflated-vs-inflated balloon).

Air only exerts pressure when moving: the bell jar demonstration makes this concrete — the sensor shows pressure even in a static, undisturbed volume. When the pump evacuates the jar, the “stillness” of the remaining air doesn’t change its pressure.

A vacuum sucks: this is the crucial one, and the PVC lid pop addresses it more effectively than any explanation. The lid does not get sucked outward. The air inside the prototype at near-atmospheric pressure pushes the lid open against the external near-vacuum. When the lid fails and students hear the rush of air flowing back in after the valve is opened, the direction of the pressure force becomes viscerally clear: it was always the higher-pressure region pushing into the lower-pressure region.

The inquiry is scaffolded through worksheets and index cards, and there is a teaching assistant present in the lab version to catch dangerous situations (the smartphone can be damaged if exposed to too low a pressure — the instructions include a warning about testing pump suction strength before risking the device).

DIY Variants for School and Home

The full lab setup is expensive and not portable. One design principle we wanted to maintain was accessibility: the experiment should work at three budget levels.

Low budget (< $5): empty food containers connected to a household vacuum cleaner through a small hole. Works, no real-time measurement visible to students.

Mid budget ($5–$50): translucent storage containers in nested sizes (large = “space”, small = “spaceship”), a small sealing ring to connect the vacuum source. Students can watch the phone display through the container during evacuation. The vacuum achieved is lower than the lab version, but the qualitative experience — the prototype holding or failing — is the same.

Expensive ($500+): the full lab version with bell jar and diaphragm pump. Best analogy, best data, highest barrier.

The DIY take-home message, as the paper puts it: be creative, fail forward. Anything that creates some vacuum and fits a prototype counts.

The experiment adapts readily to e-learning contexts: each group builds a prototype, tests it (or has a family member film it), and presents the outcome — including why the first prototype failed and how the second was improved — in a shared video conference.

A Note on Where This Fits

“Mission to Mars” grew out of the astro-lab at the University of Cologne, the same student laboratory context as the exoplanet transit experiments. The common thread is not the specific physics topic (air pressure here, photometry there) but the experimental approach: smartphones as real measurement instruments, everyday materials as apparatus, an astronomical context that sustains engagement, and a design-build-test cycle that forces students to encounter the physics physically rather than only propositionally.

The air pressure content connects naturally to the exoplanet unit at a curriculum level: habitability of exoplanets depends partly on atmospheric pressure. In the Fremde Welten article, atmospheric pressure is listed as one of the factors that determine whether a detected exoplanet could support life — an explicit cross-link between the two units.

The astro-lab@home post describes how the broader astro-lab programme — including this experiment — was adapted for home use during the pandemic. The air pressure experiment is among the more challenging to replicate at home, but the low-budget vacuum cleaner variant makes a version of it possible.

The design-build-test structure of this experiment also ended up at the centre of a methodological argument during my thesis work. The short version: everyone told me to use grounded theory instead of design thinking as the research framework, and they were right to do so. That story is in a separate post.

References

Spicker, S. J., Küpper, A., & Bresges, A. (2022). Mission to Mars: Concept and implementation of a design-based (hands-on) smartphone experiment helping students understand the effects caused by differences in air pressure. The Physics Teacher, 60(1), 47–50. https://doi.org/10.1119/10.0009109

Küpper, A., & Schulz, A. (2017). Schülerinnen und Schüler auf der Suche nach der Erde 2.0 im Schülerlabor der Universität zu Köln. Astronomie+Raumfahrt im Unterricht, 54(157), 40–45.

Staacks, S., Hütz, S., Heinke, H., & Stampfer, C. (2018). Advanced tools for smartphone-based experiments: phyphox. Physics Education, 53(4), 045009. https://doi.org/10.1088/1361-6552/aac05e

Sjoberg, S., & Schreiner, C. (2010). The ROSE project: An overview and key findings. University of Oslo.

Changelog

• 2025-10-03: Updated the self-citation to the correct year (2022), volume/issue (60(1)), pages (47–50), and DOI (10.1119/10.0009109).