Domain: Natural Science — Physics
Target concept: Pressure and Bernoulli's Principle

Video generation prompt: Hold two pieces of paper in your hands, allowing them to hang freely, and blow air downward between the two sheets of paper.

Evaluation guide:
(i) Target concept: Pressure differential due to fluid velocity gradient causing net inward force on adjacent flexible surfaces.
Minimum mechanism: Two compliant, lightweight, vertically suspended planar objects; unobstructed airflow path confined between them; sufficient flow velocity to induce measurable pressure drop relative to ambient; no external constraints preventing inward motion.
(ii)Storyline: [Phase 1: Baseline] Papers hang freely, parallel, visibly separated; full-length view, static hands, ambient lighting. [Phase 2: Trigger] Mouth approaches top of gap, lips purse, exhalation begins; airflow distortion appears *only* in inter-paper region. [Phase 3: Effect] Both papers simultaneously deform inward along vertical axis, narrowing gap until contact/near-contact; motion must be symmetric, continuous, and confined to lateral displacement. [Phase 4: Sustain] Converged state persists *only* while airflow continues: no drift, rebound, or asymmetry. [Perspective constraint]: Fixed frontal camera angle showing full paper height, hands, mouth, and inter-paper region; no occlusion of critical zones during any phase.

Manual:
Experimental Procedure
1. Hold two identical rectangular sheets of plain paper vertically, side-by-side, pinched lightly at the top edges with both hands.
2. Let both papers hang freely downward, maintaining a small visible gap between them.
3. Lean slightly forward and blow steadily downward into the gap between the papers.
Observation of Experimental Phenomena
Both papers move inward and come into contact (or nearly contact) with each other during blowing.
Summary of Experimental Principles
When air flows rapidly between two objects, pressure decreases in that region (Bernoulli’s Principle); surrounding higher-pressure air pushes the objects together.

Prompt Grounding rubric:
level_1: No two sheets of paper visible; no human hands holding papers; no downward airflow action (e.g., no mouth, no blowing motion, no air stream visual cue); scene does not depict free-hanging paper configuration.
level_2: Two sheets of paper are present and held by hands, but papers are not freely hanging (e.g., rigidly stretched, taped, or pressed together); or airflow action is present but not directed downward between the papers (e.g., blowing sideways, upward, or at one paper only).
level_3: Two sheets of paper are held side-by-side in human hands, both hanging freely with visible vertical orientation and separation at top; downward airflow action is clearly performed between them (mouth positioned above gap, lips pursed, visible exhalation motion or air disturbance), and papers remain in same spatial arrangement throughout the action.
level_4: All elements of 3-score are satisfied, AND papers are identically sized, rectangular, and visibly unmodified (no cuts, folds, tape, or attachments); hands hold papers only at top edges; airflow originates exclusively from mouth (not fan, tube, or off-screen source); viewpoint remains fixed and frontal, showing full length of both papers.
level_5: All elements of 4-score are satisfied, AND papers begin fully separated (visible gap between them before airflow), maintain consistent top-edge alignment during entire sequence, and airflow action is continuous and synchronized with observable exhalation (no pause, restart, or mismatch between breath motion and air effect onset).

Scientific and Causal Correctness rubric:
level_1: The two hanging papers do not move toward each other at any point during blowing: they stay still, sway apart, or drift together only randomly, with no relation to when the person blows (for instance, they touch before the person starts exhaling, or while the person is only inhaling).
level_2: The papers respond to the blowing, but the response contradicts the effect being tested: for example, the two sheets bow outward and further apart while air is blown between them, or only one sheet swings inward while the other stays vertical, or the sheets swing together only well after the exhalation has already stopped rather than while air is still flowing.
level_3: Both papers visibly bow inward toward the centerline of the gap while air is being blown between them, coming into contact or near-contact before the blowing ends; this inward motion clearly starts only after exhalation begins (not beforehand); both sheets stay flat and uncreased rather than folding or crumpling.
level_4: Everything described at the 3-point level holds, and in addition both sheets bow inward at a visibly comparable pace (neither sheet lags far behind or travels much further than the other), the sheets stay together or nearly touching for at least two-thirds of the time air is flowing, and neither sheet springs back apart or twists sideways while the air is still moving.
level_5: Everything described at the 4-point level holds, and in addition the sheets begin curving inward as soon as the blowing starts, with no stretch of time where air is clearly flowing but the papers have not yet begun to move; the gap closes to full contact or to a gap too narrow to see any daylight between the sheets; and the sheets keep the same vertical, untwisted orientation from before the blowing through the moment they meet.

Spatiotemporal Consistency rubric:
level_1: A hand or the mouth abruptly appears in the frame with no approaching motion, as though placed there between one frame and the next; a paper's edge tears, fragments, or turns see-through with no physical cause; the wall or backdrop behind the person switches to a different setting partway through the clip; the whole scene freezes for a beat and then skips ahead; or the room's lighting suddenly flashes brighter or plunges darker with no visible cause between otherwise consistent frames.
level_2: A paper stretches, shrinks, or bends in a way real paper cannot; a hand's grip position on its sheet shifts noticeably between frames without any visible hand motion causing the shift; the visible air disturbance between the sheets is present in one frame and simply absent in the next instead of fading out gradually; the camera's framing drifts or resets partway through the clip.
level_3: The paper edges show a slight, jittery flicker frame-to-frame even though the sheets are otherwise converging as expected; the hands show a small, unnatural tremor unrelated to steady holding or blowing; the visible air disturbance between the sheets is patchier near the paper edges than in the middle of the gap, but it never disappears outright and neither sheet breaks its shape.
level_4: The paper sheets move as smooth, continuous surfaces throughout, with no warping, tearing, or edge flicker; the hands hold the top corners steadily, showing only the small natural movement of a real grip; the air-disturbance region between the sheets grows and shifts smoothly as the papers converge, staying confined to the gap; the camera's framing and the backdrop never shift or reset during the clip.
level_5: Everything described at the 4-point level holds, and further, the sheets' inward swing follows one smooth, unbroken path from their starting position to contact, with no stalling, reversing, or overshoot-and-correct; the hands stay in the same top-edge grip from before the blowing begins until after the sheets meet; and the visible air disturbance strengthens gradually and evenly across the whole gap as the blowing continues, rather than surging or flickering in patches.