Domain: Engineering — Geotechnical Engineering
Target concept: A Comparative Study of Wind Transport of Sand and Dust in a Simple Fan-Driven Device

Video generation prompt: On a table, two adjacent trays containing coarse sand and fine dust are placed; a household fan is blowing continuously on them for several seconds.

Evaluation guide:
(i) Target concept: Loose fine dust becoming airborne under fan-driven airflow while coarser, heavier sand grains stay put: a mass/drag contrast between two loose, non-cohesive granular materials, not a general particle-size threshold law for wind entrainment.
Minimum mechanism: The sand and dust must both be dry, loose, and uncompacted (no crust, no moisture binding), so ordinary differences in grain mass and drag (not cohesion) govern which material moves; the fan's airflow must be strong enough to lift the much lighter dust particles once dislodged, while staying well below the far higher airflow needed to dislodge the heavier sand grains; the trays must be open-top and level so confinement does not hold either material down.
(ii)Storyline: Frame 1–2: Static wide shot showing table, two adjacent trays (left = coarse sand, right = fine dust), powered fan facing them. Frame 3–5: Fan activates. Blades begin rotating, airflow initiates (visible via dust surface ripple or hair/fabric movement if present). Frame 6–8: Fine dust detaches en masse, rises vertically then disperses; coarse sand surface remains intact with zero grain displacement. Frame 9–10: Sustained airborne dust plume visible above right tray; left tray unchanged; fan running continuously; fixed frontal viewpoint maintains side-by-side spatial relationship without occlusion.

Manual:
Experimental Procedure
1. Place a stable table in well-lit indoor setting.
2. Position two identical shallow rectangular trays side-by-side on the table.
3. Fill left tray with coarse sand (grains visibly large, gritty, non-flowing).
4. Fill right tray with fine dust (powdery, homogenous, easily airborne).
5. Place household fan 30–50 cm directly in front of trays, aimed centrally at both.
6. Turn fan on to medium setting and maintain continuous airflow for full duration.
Observation of Experimental Phenomena
- Coarse sand remains fully settled: no grain lifts, rolls, or saltates; only possible minor vibration.
- Fine dust lifts immediately: forms visible airborne plume rising above tray rim, dispersing horizontally.
- Clear contrast between trays: static sand vs. suspended dust, confirming differential entrainment.
Summary of Experimental Principles
Whether a grain lifts off in a moving airstream depends on the balance between the aerodynamic force the air exerts on it and the grain's own weight (plus any cohesion holding it to its neighbors). Here, both the sand and the dust are loose, dry, and uncompacted, with no crust or moisture binding the grains together, so cohesion plays essentially no role and the much lower mass of each dust particle is what lets the same airflow lift and carry it, while the far heavier sand grains stay put. This should not be read as a general rule that fine dust always requires less wind than sand to become airborne: in many natural settings, fine dust and silt are cohesive (held together by moisture, electrostatic attraction, or van der Waals forces) and in fact need a higher threshold wind speed than mid-sized sand grains do, which is why natural dust storms usually rely on coarser, saltating sand grains bombarding the surface to knock fine dust loose rather than on direct aerodynamic lift. The loose-powder setup used in this demonstration removes that cohesion, which is why the simple mass/drag contrast between sand and dust is what shows up on camera.

Prompt Grounding rubric:
level_1: No table is shown, or there are not two separate trays (e.g., only one tray, or a single tray holding both materials), or no fan is present, or the sand and the fan-blown dust are not both visible as distinct materials, or the fan never visibly turns for the whole clip (blades stay still, no cord/switch, no sign it is running).
level_2: Table, two trays, and a fan are all present, but the setup is wrong in some way: the sand tray and the dust tray are not next to each other (a gap wider than a tray separates them, or they sit on different surfaces), or the fan faces away from the trays rather than toward them, or the sand and dust are poured together into one tray instead of being kept in two separate trays.
level_3: The table is steady; the sand tray and the dust tray sit side by side on the same tabletop, each holding only its own material; the fan is switched on, aimed at the pair of trays, and its blades are visibly turning for at least part of the clip.
level_4: All 3-point conditions hold; additionally the fan keeps blowing toward the trays for the whole clip without stopping, reversing, or turning aside; the sand tray stays on its original side relative to the dust tray without the two swapping places or drifting apart across the table; and both trays plus the fan stay in view (none of them leaves the frame or is blocked from sight) for the entire clip.
level_5: All 4-point conditions hold; additionally the same single fan (one housing, one blade assembly) and the same two trays are used throughout with no substitution or duplication of any of them; the coarse, gritty look of the sand and the fine, powdery look of the dust both stay clearly recognizable in their own trays; and the clip keeps one continuous wide frontal shot that shows table, both trays, and fan together, with no cut to a different camera angle.

Scientific and Causal Correctness rubric:
level_1: What is shown contradicts basic wind-entrainment physics for this setup: e.g., the coarse sand tray is the one that shows grains lifting into the air while the fine dust tray stays undisturbed, or the sand and dust respond in exactly the same way (no difference in behavior at all) despite the fan clearly running, or dust is shown airborne before the fan is shown turning.
level_2: The fan is visibly running but neither tray shows any particle response, or any particle motion that does appear moves the wrong way (e.g., grains appear pulled toward the fan instead of pushed away from it), or the sand grains bounce/roll noticeably while the dust stays inert, or the dust clumps into rolling pellets rather than any of it becoming airborne.
level_3: The fan blows steadily toward both trays; the sand grains show at most a slight in-place vibration, with no grain leaving the sand pile; some dust visibly lifts off its pile, but the lofting is on-and-off rather than sustained: it starts and stops repeatedly, or the dust only hops along the tray floor without any of it clearly rising above the tray's rim.
level_4: All 3-point conditions hold; additionally no sand grain is ever seen leaving the sand pile; dust particles rise and travel above the tray's rim in a visibly continuous stream for a sustained stretch of the clip; and the order of events is correct throughout: dust only becomes airborne after the fan is shown running, never before.
level_5: All 4-point conditions hold; additionally the sand pile shows no grain motion of any kind (no vibrating, rolling, or hopping) for the entire clip; the dust forms a visibly continuous rising cloud that stays aloft above the tray rather than repeatedly falling back into clumps; and no dust is shown drifting over and settling onto the sand tray.

Spatiotemporal Consistency rubric:
level_1: A severe break in scene continuity occurs: e.g., one of the two trays, or the fan, is missing from its spot and shows up elsewhere (or not at all) between shots with no hand or process shown moving it; the overall light in the scene swings from bright to dark (or day-like to night-like) within a single cut, with no lamp, cloud, or switch shown causing it; the sand or dust turns into a visibly different material (sand becoming gravel, dust becoming flour, or either turning liquid) with no process shown causing it; or the view cuts to a clearly different camera angle with no camera motion shown to explain the change.
level_2: A noticeable but less severe break occurs: e.g., a tray is briefly hidden behind something and comes back in a different spot on the table than where it started; the fan blades stop turning and then resume at a different rotational position with no in-between motion shown; the fan casts a shadow on the tabletop that swings to point a different way even though neither the fan itself nor the room lighting appears to move; or the visible grain size or color of the sand or dust changes abruptly partway through the clip.
level_3: A minor, only just noticeable slip occurs: e.g., a tray or the fan shows a small position wobble that does not change its overall place on the table; overall brightness flickers briefly without ever hiding or revealing any grains; the fan blades' spin looks slightly uneven for a moment while clearly still spinning; but no tray or the fan disappears, swaps place, or is replaced by anything else.
level_4: All 3-point conditions hold; additionally neither tray nor the fan shows any wobble, drift, or flicker at all; the fan blades spin at a steady, even rate for the whole clip; the tray rims and fan housing keep sharp, stable outlines rather than blurring or warping; and as the dust cloud grows and thickens above its tray, the direction and darkness of the shadows the fan and trays cast on the table do not change. The developing dust cloud does not itself appear to shift the lighting on the sand side.
level_5: All 4-point conditions hold; additionally the blur on the spinning fan blades and on the rising dust particles matches how fast they are actually moving (neither is shown frozen sharp while clearly in fast motion, nor smeared into a streak while moving slowly); the dust tray never appears to sit closer to or farther from the camera than the sand tray in a way that shifts as the clip plays; and the matte tray and tabletop surfaces show no shiny reflections that would only appear on polished or wet material.