Domain: Natural Science — Physics
Target concept: A circular tympanic membrane vibrating in an intrinsic mode shape

Video generation prompt: A circular eardrum sprinkled with fine sand is continuously driven by a mechanical vibrator at a fixed frequency during vibration.

Evaluation guide:
(i) Target concept: Standing wave formation on a 2D bounded elastic membrane under harmonic point excitation.
Minimum mechanism: Membrane must be isotropic, uniformly tensioned, and free of damping sufficient to sustain observable modes; vibrator must provide sustained, narrowband mechanical input at resonance; sand must be light enough to be displaced by surface acceleration but heavy enough to settle at nodes.
(ii)Storyline: [Phase 1] Static start: intact circular membrane fully covered with evenly distributed sand; vibrator idle and in contact. [Phase 2] Activation: vibrator engages → membrane begins oscillating → sand grains initiate small-amplitude jitter. [Phase 3] Redistribution: sand migrates away from high-acceleration zones (antinodes) toward low-acceleration zones (nodes) → clumps form, bare lines emerge. [Phase 4] Stabilization: clumps and nodal lines reach steady configuration matching intrinsic mode geometry; pattern persists unchanged under sustained drive. [Phase 5] Visibility constraint: fixed frontal orthographic view; no occlusion; full membrane, full sand coverage, full vibrator contact zone always in frame; no close-ups or cutaways.

Manual:
Experimental Procedure
1. Mount a thin, taut circular membrane (eardrum analog) horizontally.
2. Sprinkle fine, dry sand evenly over its entire surface.
3. Attach a mechanical vibrator firmly to the membrane rim or center.
4. Activate vibrator at fixed frequency and sustain continuously.
Observation of Experimental Phenomena
Sand migrates from vibrating regions and accumulates into stable clumps, leaving behind continuous bare regions (nodal lines) arranged in symmetric patterns (e.g., circles or straight lines) across the membrane.
Summary of Experimental Principles
A driven circular membrane vibrates in intrinsic mode shapes; nodal lines are loci of zero displacement where sand remains, while antinodes (max displacement) eject sand to adjacent nodes.

Prompt Grounding rubric:
level_1: No circular membrane, no mechanical vibrator, and no sand appear in any frame; there is no shot of a driving action of any kind.
level_2: Only one of the three (the membrane, the vibrator, or the sand) appears on its own; the vibrator is never shown touching the membrane, and no sand is shown resting on the membrane's surface.
level_3: The circular membrane, a vibrator touching its edge or center, and a layer of sand across its surface are all visible together, with the vibrator shown running against the membrane while the sand sits on top, all within one continuous framing.
level_4: Everything required for a 3 holds, and in addition the vibrator stays in contact with the membrane for the whole clip, the sand stays only on the membrane's surface (none scattered onto the vibrator or the surrounding mount), the membrane's circular edge stays intact with no tearing or curling, and no hands, tools, or labels intrude into the shot.
level_5: Everything required for a 4 holds, and in addition the sand settles into a pattern of clumps and bare patches that holds still (not drifting, sliding, or continuing to redistribute) for at least about 3 consecutive seconds by the end of the clip, with the grain boundaries and membrane edge sharp enough to see clearly (no motion blur obscuring them).

Scientific and Causal Correctness rubric:
level_1: The sand shows no response to the vibrator's action: it stays spread evenly or moves randomly regardless of whether the vibrator is running; the membrane shows no visible deformation; or the physics breaks down entirely (e.g., sand flies off the surface, the membrane appears to liquefy, the vibrator spins freely without ever coupling to the membrane).
level_2: The vibrator is running and the membrane is visibly deforming, but the sand doesn't organize into any pattern: it jitters uniformly, slides off as one mass, or doesn't move at all; or the sand does redistribute, but only while the vibrator is switched off, reversing the expected cause and effect.
level_3: While the vibrator is actively running, the sand redistributes into clearly separated regions (dense clumps in some areas, bare strips or arcs in others), and this bare-versus-clumped pattern traces out lines or curves across the membrane rather than a random scatter; the membrane's motion looks like back-and-forth vibration, not sliding or spinning.
level_4: Everything required for a 3 holds, and in addition the bare (nodal) lines form unbroken paths all the way across the membrane, the clumped sand sits still at its location rather than creeping or rolling, sand doesn't pile up at the vibrator's contact point unless that point happens to fall on a bare line, and the membrane's movement stays a flat in-plane flex with no buckling or flapping out of the drum's plane.
level_5: Everything required for a 4 holds, and in addition the bare-line pattern matches a genuine vibrating-membrane mode shape (for example a full circular ring near the rim with the center still clumped, or two or more straight bare lines crossing through the center at even angles); sand never crosses over a bare line once the pattern has settled, and all sand motion stops as soon as the vibrator is switched off (if that moment is shown).

Spatiotemporal Consistency rubric:
level_1: The membrane or the vibrator is absent from one frame and present again in a later one with no transition shown; the sand's layout jumps straight from one arrangement to a completely different one with no grains seen moving between them; or the scene cuts to a different camera angle or flashes to total darkness mid-sequence.
level_2: One clear continuity break occurs: the vibrator loses contact with the membrane and then snaps back onto it with no transition shown; the sand's pattern changes to a new configuration between two frames with no grains visibly in motion; or the membrane's surface flickers between two different shapes from one frame to the next.
level_3: The vibrator stays fixed against the same point on the membrane, the sand stays on the membrane's surface the whole time without floating above it or sinking beneath it, the membrane keeps its round, flat outline, and the sequence runs as one continuous shot with no cuts or sudden viewpoint changes.
level_4: Everything required for a 3 holds, and in addition the membrane's surface motion looks smooth and evenly repeating rather than jerky or snapping, the sand clumps keep their shape and stay in the same spot on the membrane as it oscillates, the vibrator never appears to pass through the membrane's surface, and every object appears to sit at the same depth relative to the camera throughout.
level_5: Everything required for a 4 holds, and in addition each point on the membrane appears to move straight up and down rather than sliding sideways, the sand clumps ride along with the local membrane motion instead of drifting independently across the surface, the membrane's circular outline keeps the same shape and proportions from frame to frame with no stretching or skewing, and any blur in the moving sand or membrane looks consistent with the vibration speed rather than appearing separately smeared.