Domain: Engineering — Geotechnical Engineering
Target concept: Take equal volumes of sandy soil and clay, place them separately on both ends of the balance, and verify that the side with the sandy soil sinks due to the noticeable weight difference.

Video generation prompt: We measured equal volumes of sand and clay using the same container, and placed them separately on the two pans of the balance. The balance was then released for comparison.

Evaluation guide:
(i) Target concept: Density-driven mass difference under equal volume constraint.
Minimum mechanism: Sandy soil must be visually higher-density (granular, compact, light-colored) than clay (cohesive, lower-density, darker/moister appearance); container must enforce volume equivalence; balance must translate mass difference into unidirectional pan motion.
(ii)Storyline: [Frame 0–2] Identical container filled with sandy soil → [Frame 3–4] Sand poured into left pan → [Frame 5–6] Same container refilled with clay → [Frame 7–8] Clay poured into right pan → [Frame 9] Balance shown level, hands withdraw → [Frame 10+] Release occurs → [Frame 11–end] Left pan descends smoothly and monotonically; right pan shows zero displacement. Fixed frontal viewpoint; all actions occur within single continuous shot; no cutaways, no inserts, no labels — visibility relies solely on object identity, spatial arrangement, and motion outcome.

Manual:
Experimental Procedure
1. Fill identical container with sandy soil; pour into left balance pan.
2. Fill same container with clay; pour into right balance pan.
3. Ensure balance is level; release gently.
Observation of Experimental Phenomena
The left pan (with sandy soil) descends continuously; the right pan (with clay) remains stationary.
Summary of Experimental Principles
Equal volumes of sandy soil and clay have different masses due to differing densities; sandy soil is denser and therefore heavier per unit volume.

Prompt Grounding rubric:
level_1: No balance is shown; neither sandy soil nor clay appears; no container is used to portion either material; neither pan ever receives a fill; there's no visual cue that two materials are being compared at all.
level_2: A balance appears but sits empty, or only one material (sand or clay, not both) is shown going into a pan, or the container is shown without ever being used to fill a pan, or sand/clay ends up somewhere other than the balance pans (e.g. left on a table); the clip never gets to the point of releasing a loaded balance.
level_3: A two-pan balance is shown; both sandy soil and clay are visibly present; the same container is used (or clearly implied to be the same) to transfer each material onto its own pan; the balance is shown being released with both pans loaded; the whole setup is framed from one fixed viewpoint with both pans visible together.
level_4: Everything in the 3-point description holds, and in addition the same container is recognizably identical in shape and size on both fills, both materials fill it to a visually matching level before being poured, the two materials are added one after the other rather than at the same time, and the balance is clearly level right before release and clearly tilted after.
level_5: Everything in the 4-point description holds, and in addition sand and clay are easy to tell apart at a glance (light, loose grains vs. darker, cohesive clay) and consistently placed on the same side each time they appear; the container is emptied out before being refilled with the second material, so there's no leftover material carried from one fill to the next; and once released, the pans stay still except for the single, continuous descent of one pan - no bouncing, stalling, or reversal.

Scientific and Causal Correctness rubric:
level_1: What's shown contradicts the physics - the clay pan sinks instead of sand, both pans stay level after release, the sand pan rises, or the materials are mislabeled outright (e.g. the loose light-colored granular material is called 'clay').
level_2: One material looks like the wrong thing (e.g. sand rendered as a fine gray powder that could pass for something else, or clay looking granular like sand), or the two portions are obviously unequal in size before being placed on the pans, or the balance is already tilted before release (suggesting it was loaded unevenly), or both pans move in a way that doesn't clearly show one side winning.
level_3: Sand and clay look visually distinct (loose light grains vs. darker cohesive clay); the two portions look like matching volumes going into the same container; the balance starts level; after release, one pan clearly goes down while the other stays put or only drifts up slightly, and the descending side is the sand - the clip supports 'equal volume, sand heavier, sand pan sinks.'
level_4: Everything in the 3-point description holds, and in addition the sand pan's descent is clear and doesn't pause, reverse, or bounce partway; the clay pan never dips downward at any point; and no hand or outside object touches either pan once release has happened.
level_5: Everything in the 4-point description holds, and in addition the sand pan's descent looks smooth and steady from the first moment it moves until it settles; the clay pan shows no visible up-or-down motion for the entire time after release; and there's no visual glitch - like a sudden shadow jump or the pan snapping to a new position - that would make a viewer doubt that the sand side is genuinely heavier.

Spatiotemporal Consistency rubric:
level_1: A severe break occurs - the balance itself disappears and reappears, the sand or clay jumps from one location to another with no transfer motion shown, the container changes size or shape between its two uses, a pan spins on its own, the whole scene's lighting suddenly switches to a different setup partway through, or the camera cuts to a new angle with no transition shown.
level_2: A clear but less extreme problem occurs - the balance arm looks like it bends unrealistically, a pan tilts without visibly pivoting, the container moves on its own without a hand touching it, sand or clay appears to float or splash upward against gravity, the motion stutters or freezes for more than a couple of frames, or a shadow appears detached from the object that should be casting it.
level_3: A small, easy-to-miss issue occurs - a brief blur during the pan's descent, a slight mismatch in where the container sits between filling and pouring, or a touch of ambient dimming/brightening that doesn't line up with any action - but nothing breaks apart, teleports, or bends, and the pans and container keep the same relative arrangement throughout.
level_4: Everything in the 3-point description holds, and in addition the whole sequence - filling, pouring, placing, releasing, descending - reads as one continuous motion; the container keeps the same orientation and size across both of its uses; the balance's pivot point doesn't drift; and no hand disappears behind a pan only to reappear inconsistently.
level_5: Everything in the 4-point description holds, and in addition the container is lifted straight up without swaying sideways; the sand pours as a steady stream rather than scattering through the air; the clay moves as one cohesive lump rather than crumbling apart; the descending pan swings smoothly about the balance's pivot with no sudden jerks; and the pan, arm, and container edges stay clean and stable throughout, without glitchy flicker or warped-looking geometry.