Experiment: Driving vs. Parked
What it demonstrates: The convection physics of Chapter 2.7 — the boundary layer, the still-air blanket, and the moving-air relief valve — measured on a single vehicle in a single afternoon. This is also the experiment Chapter 2.7's honesty caveat deferred to: the mechanism is settled physics, the magnitudes are best established by direct measurement, and this is the direct measurement.
Requirements: A vehicle with film. An infrared thermometer. A sunny day, a stretch of highway, and a sunny place to park.
Protocol:
- Drive at highway speed for 20–30 minutes — ventilation off, windows closed, sun on the filmed glass.
- At the stop, immediately measure the inner surface of the filmed glass at a marked point. This is the in-motion reading, taken while convection's effect is still present in the glass.
- Park in continued identical sun exposure. After 30 minutes still, measure the same marked point. This is the parked reading.
- Record both, plus all conditions.
Reading the results. The difference between the two readings is the convective effect made visible: the heat that moving air was continuously stripping from the glass, now accumulating under the still-air blanket. Per Chapter 2.7, the size of the difference also speaks to mechanism — an absorption-dominant film holds substantial captured energy for convection to remove, so its parked reading climbs well above its in-motion reading; a reflection-dominant film captures less, leaving less for airflow to carry away, so its two readings sit closer together.
A single afternoon, two readings of one pane, and the experimenter has measured both a chapter of heat-transfer physics and — echoing Chapter 5.4 — a second independent fingerprint of the film's mechanism. Repeated across seasons and speeds, the pattern belongs in the journal.
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