Domain: Natural Science — Physics
Target concept: Colored objects sink through the tank, demonstrating the loss of color with increasing depth.

Video generation prompt: In a clear tank, visually identical red and blue objects are slowly lowered from the water surface to the bottom of the tank using thin ropes, side by side.

Evaluation guide:
(i) Target concept: Wavelength-selective attenuation of visible light in aqueous medium.
Minimum mechanism: Water must act as a dispersive absorptive medium where red light (600–700 nm) undergoes significantly higher extinction than blue light (450–495 nm) per unit path length; objects must be spectrally neutral emitters/reflectors (i.e., no phosphorescence, fluorescence, or active illumination); viewing must occur through water column, not air.
(ii)Storyline: Frame 1: Two identically shaped red and blue objects suspended side-by-side just above water surface, ropes taut, tank fully visible. → Causal transition: Descent begins → Frame mid-sequence: Red object appears washed-out or grayish while blue retains hue, both at same submersion depth. → Causal transition: Continued descent → Frame near bottom: Red object is achromatic (no hue discernible), blue object still shows clear blue identity. → Visibility constraint: Fixed frontal viewpoint; no occlusion; water clarity sufficient to resolve object outlines and hue at all depths; no external lighting interference (e.g., colored gels, strobes).

Manual:
Experimental Procedure
1. Fill a tall, clear rectangular tank with clean water.
2. Suspend one red object and one blue object—identical in size, shape, and material—on separate thin, transparent ropes.
3. Position them side-by-side just above the water surface.
4. Lower both simultaneously and steadily to the tank bottom.
Observation of Experimental Phenomena
Red object visibly loses color saturation earlier and more completely than blue object during descent; blue object remains discernibly blue at depths where red appears gray or achromatic.
Summary of Experimental Principles
Colored objects sink through the tank, demonstrating the loss of color with increasing depth due to wavelength-dependent absorption and scattering of light in water: longer wavelengths (red) attenuate faster than shorter ones (blue).

Prompt Grounding rubric:
level_1: No transparent tank appears; neither a red object nor a blue object is shown; nothing is lowered from the water's surface; no ropes are visible; the clip never shows the lowering action at all.
level_2: A tank with water is shown, but only one of the two objects (red or blue) appears; no rope is attached to either object, or the object simply sits static at the surface or the bottom rather than being lowered; the two objects are never shown descending together at the same time.
level_3: A clear tank filled with water is shown; a red object and a blue object are both present, each tied to its own thin rope; both objects start at the water's surface and are lowered toward the bottom; throughout the descent they stay next to each other within the same shot rather than one being out of frame.
level_4: Everything at level 3 holds, and in addition: both objects stay fully visible for the whole descent, never hidden behind the tank's edge or by anything else in the shot; both ropes stay taut and roughly vertical the entire time; no hand, tool, or other object ever enters the frame.
level_5: Everything at level 4 holds, and in addition: the red and blue objects match each other in size, shape, and surface texture (for example, both are smooth spheres of the same diameter); they stay level with each other and equally spaced from the tank's side walls throughout the descent; both ropes start at the same height above the water at the very beginning; and the viewpoint never swings, tilts, or warps in a way that would be inconsistent with a single fixed camera.

Scientific and Causal Correctness rubric:
level_1: Neither object loses any color saturation as they descend: both stay fully vivid from surface to bottom; or one or both objects change to a completely different hue (for example the red object turning green); or all color is lost instantly rather than progressively; or any color loss happens only before the objects enter the water or only after they've already reached the bottom, never during the descent itself.
level_2: Only one of the two objects (red or blue) shows any fading; or both objects fade by the same amount at every depth (no difference between them); or the red object's fading finishes by mid-tank rather than continuing toward the bottom; or the color briefly returns after starting to fade; or the two objects look different in finish or material in a way unrelated to the color-loss effect (for example one looking glossy and the other matte).
level_3: Both objects progressively lose color saturation as they descend; at any given depth the red object looks noticeably more washed out and gray than the blue object, which still reads clearly as blue; the amount of color lost tracks how deep each object is, not how long the clip has been running or how fast the objects are moving.
level_4: Everything at level 3 holds, and in addition: the red object reaches a fully gray, hue-less appearance before the blue object reaches a comparable loss of color; the blue object still clearly reads as blue at the depth where the red object has already gone gray; and the color loss never reverses or flickers back and forth as the objects continue down.
level_5: Everything at level 4 holds, and in addition: the red object is the one that visibly grays out first and most completely, consistent with red light being absorbed faster than blue light in water; the blue object never grays out before or as fast as the red one; the red object never appears to shift toward brown, purple, or any hue other than gray as it loses color; and the brightness and contrast of both objects change only in a way consistent with dimming through more water above them, without any added artificial brightening or edge sharpening as they descend.

Spatiotemporal Consistency rubric:
level_1: One or both objects suddenly jump from one position to another instead of moving continuously; a rope snaps, vanishes, or reappears out of nowhere; the water's surface abruptly changes level or shape from one frame to the next; the lighting suddenly switches from dim to bright or back; the tank itself changes shape or proportions; or an object's size or rotation changes in a way that doesn't match its motion.
level_2: The descent looks choppy, as if frames were skipped; a rope that was slack suddenly goes taut with no smooth stretching motion in between; ripples on the water surface appear or vanish for no reason; an object overlaps or passes through the tank wall or the other object; or one object keeps moving while the other stays frozen in place for a noticeably long stretch.
level_3: Both objects sink smoothly and continuously, without jumping, freezing, or moving backward; both ropes stay attached and taut the whole way down; the water surface stays essentially calm, with only minor natural ripples; the tank and the camera's framing stay fixed; neither object ever appears clipped by the tank edges or broken apart.
level_4: Everything at level 3 holds, and in addition: the two objects descend at a visibly similar pace, with neither one pulling more than roughly one object-length ahead of the other; both ropes stay vertical and roughly parallel to each other; any highlights or reflections on the objects shift smoothly and in step with their motion rather than jumping or lagging; and the ropes and tank markings stay clear and steady rather than shimmering or flickering as the objects move.
level_5: Everything at level 4 holds, and in addition: the apparent distance between the objects and the tank's back wall stays constant, with no sense of the camera drifting closer or farther away; the ropes appear to bend slightly where they cross the water's surface, consistent with light refracting at the boundary, and this bending stays consistent from frame to frame; any motion blur on the descending objects points in the same direction as their downward motion; and the edges of both objects and both ropes line up smoothly from one frame to the next with no doubling or misalignment.