Domain: Natural Science — Physics
Target concept: Extension and Recovery of Rubber Bands Under Cyclic Stretching

Video generation prompt: A person pulls a rubber band with both hands, repeatedly stretching it by moving the hands apart and then releasing them back to the initial hand position.

Evaluation guide:
(i) Target concept: Reversible elastic deformation of polymeric material under cyclic tensile load.
Minimum mechanism: The rubber band must be composed of entangled polymer chains that straighten under tension and recoil spontaneously upon force removal; no bond breaking or slippage; thermal motion enables recovery; ambient temperature must be above glass transition temperature of rubber.
(ii)Storyline: Frame 0–start: Hands stationary, rubber band slack and coiled/unstretched, centered in view. → Stretch phase: Hands move apart steadily; rubber band elongates linearly, maintaining cylindrical symmetry and uniform thickness reduction. → Hold: Rubber band remains taut, no sag or vibration. → Release phase: Hands move inward steadily; rubber band shortens continuously, regaining original length and shape. → Recovery: Full return to pre-stretch dimensions before next cycle begins. Perspective: Fixed frontal, eye-level, centered composition; hands and rubber band always fully in frame; no camera motion or angle shift.

Manual:
Experimental Procedure
1. Person places thumbs and index fingers of both hands on opposite ends of a plain, unstretched rubber band.
2. Slowly moves hands apart to stretch the rubber band visibly.
3. Holds stretched position briefly.
4. Slowly brings hands back together until rubber band returns to original unstretched length.
5. Repeats steps 2–4 at least once more.
Observation of Experimental Phenomena
The rubber band elongates uniformly when hands move apart and shortens uniformly when hands move together; it fully recovers its original length after each release; no permanent deformation occurs across cycles.
Summary of Experimental Principles
Rubber bands exhibit elastic behavior under cyclic loading: they deform reversibly within their elastic limit, obeying Hooke’s law approximately, and recover completely upon unloading—demonstrating energy storage and release without plastic deformation.

Prompt Grounding rubric:
level_1: No hands appear in the scene, or no rubber band is present, or neither a stretching nor a releasing motion occurs; the scene shows unrelated objects, a static image, or something other than the described action.
level_2: A hand or rubber band appears, but not the full setup described: e.g., only one hand is visible, or the rubber band lies unheld on a surface, or the hands move apart/together without any rubber band connecting them.
level_3: Two hands are visible, each gripping one end of a single rubber band; the hands move apart and then move back toward each other at least once; the start and end framing of this cycle may be loosely defined.
level_4: Two hands hold opposite ends of exactly one rubber band throughout; the hands move apart continuously, then move back continuously to roughly their starting separation, completing at least one full stretch-then-release cycle with the hands never losing contact with the rubber band; no unrelated object blocks the view of the hands or band.
level_5: Two hands hold opposite ends of exactly one rubber band and never lose grip; the hands move apart smoothly, then return smoothly to the same starting separation, repeating this stretch-release cycle at least twice in a row without interruption; the rubber band is visibly taut at full stretch and visibly slack at full release each time; no extra hand, limb, or object enters the frame and the action is not cut or skipped.

Scientific and Causal Correctness rubric:
level_1: The rubber band's length does not change as the hands move, or it changes without any hand movement, or once stretched it stays elongated after the hands return to the starting separation (permanent deformation).
level_2: The rubber band's length changes, but not in the correct direction at least once (e.g., it visibly shortens while the hands are separating, or lengthens while the hands come together), or its length changes in sudden jumps rather than gradually, or it stays partly stretched after the first release instead of returning to its original length.
level_3: The rubber band visibly lengthens each time the hands move apart and visibly shortens each time the hands move together, with the length change clearly following the hand motion in direction; across at least one full cycle it returns to a length close to its starting length with no obvious leftover stretch.
level_4: The rubber band's lengthening during separation and shortening during reapproach are both gradual, not stepwise; after every release across all shown cycles the band returns fully to its original pre-stretch length, with no visible residual stretch carried into the next cycle, and every cycle behaves the same way.
level_5: The rubber band lengthens and shortens smoothly and evenly along its whole length, with no one section stretching faster than another; it returns to exactly its starting length and shape after every single release with zero visible leftover stretch between cycles; it never buckles, kinks, or bows sideways during stretching or relaxing.

Spatiotemporal Consistency rubric:
level_1: The rubber band or either hand jumps to a different position or orientation between consecutive frames; the rubber band vanishes mid-stretch and reappears elsewhere; the scene's overall brightness or the rubber band's cast shadow switches abruptly with no hand or camera movement to explain it; the background behind the hands shifts or rotates on its own.
level_2: Hand or rubber-band motion shows visible skipped frames or stutter-stepping; the rubber band blinks out of view for at least one frame during the stretch or release; one hand or one end of the rubber band is persistently hidden behind the other hand or an object with no in-scene reason; the camera view wobbles, tilts, or zooms without any stated reason.
level_3: Both hands and the full length of the rubber band stay visible for the whole clip; hand and rubber-band motion is continuous, with no teleporting jumps or dropped frames; the light source's direction and the rubber band's shadow keep the same brightness and orientation throughout; the surface or background behind the hands does not shift; brief, small hand tremor is acceptable.
level_4: Hands stay at a fixed horizontal spacing from the frame center and the rubber band stays centered between them, with no unexplained rotation or resizing of the scene; during each stretch phase the hands move steadily apart without reversing direction, and during each release phase they move steadily together without reversing; the rubber band's outline never tears, splits, or warps into an implausible shape.
level_5: Across the full clip the hands' separating and closing motion is visibly smooth with no stutter or skipped step; the rubber band's edge stays clean and continuous as it lengthens and shortens, with no flicker, shimmer, or momentary doubling of its outline; the shadow cast by the hands and rubber band shifts gradually and in a physically sensible way as the hands move; the background stays completely fixed and unchanging behind the action.