Domain: Engineering — Materials Science & Engineering
Target concept: The rubber strip exhibits recovery after stretching, in contrast to the brittle plastic strip that undergoes cracking.

Video generation prompt: The red rubber strip on the left and the transparent plastic strip on the right are clamped at one end, stretched to a similar length, and then released.

Evaluation guide:
(i) Target concept: Elastic recovery vs. brittle fracture under tensile loading.
Minimum mechanism: The rubber strip must possess enough entropic elasticity to store strain energy reversibly and recoil back to its original length once released. The plastic strip must have low fracture toughness, so that the tensile stress it experiences while being stretched (at or near its point of maximum elongation) exceeds its fracture strength and produces a crack during or at the peak of the stretching motion itself, rather than only after the strips are released.
(ii)Storyline: Frame 0–2: Static shot showing the two strips clamped side by side (red rubber on the left, transparent plastic on the right). Frame 3–6: Both strips are stretched synchronously; the rubber elongates smoothly and without damage, while the plastic strip develops a visible crack as it nears its maximum elongation. Frame 7–8: Both strips are released at the same visual moment. The rubber strip begins recoiling immediately toward its original length; the plastic strip, already cracked, shows no recoil at the break. Frame 9–10: Final stable state. The rubber strip has fully recovered its original shape and length; the plastic strip retains an open, visible crack that never closes. Viewpoint: fixed frontal shot with no parallax, consistent framing, full-strip visibility throughout.

Manual:
Experimental Procedure
1. Clamp the red rubber strip at its left end and the transparent plastic strip at its right end — both fixed side-by-side in the same plane.
2. Simultaneously stretch both strips until they reach a similar visible length.
3. Release both strips at the same time.
Observation of Experimental Phenomena
- The red rubber strip elongates smoothly throughout the stretch and, upon release, snaps back to its original length and shape.
- The transparent plastic strip, being brittle, develops a visible crack as it approaches its maximum elongation — the crack forms under the peak tensile stress of the stretch itself, at or before the point of release — and the strip does not recover; the crack remains open in the final state.
Summary of Experimental Principles
Rubber is an elastomer: its long, coiled polymer chains allow reversible deformation, so it stores strain energy and recoils back to its original shape once released. The plastic strip is brittle and lacks this ductility; once the tensile stress from stretching exceeds its fracture toughness, a crack nucleates and propagates immediately, so the fracture occurs at or near peak elongation rather than only after unloading.

Prompt Grounding rubric:
level_1: No clamped strips visible; or only one strip type present; or no stretching/release action shown; or strips not positioned left/right as specified; or red rubber strip absent or not red; or transparent plastic strip absent or not transparent.
level_2: Strips present and roughly positioned left/right, but at least one of: red rubber strip is not red (e.g., pink, orange, gray), or transparent plastic strip is opaque/colored, or clamping is missing on one or both ends, or stretching action is absent (no visible elongation), or release action is absent (no visible return or fracture).
level_3: Red rubber strip appears on left, transparent plastic strip appears on right, both are clamped at one end, and both undergo one stretching motion (visible elongation) followed by release (visible post-release state); all objects present in correct type, color, quantity, and spatial arrangement per prompt.
level_4: Everything described for the 3-point level holds, and in addition: stretching is applied synchronously to both strips (same start and end timing of elongation), release is triggered at the same visual moment for both strips, and the side-by-side spatial relationship between the two strips is maintained continuously without shift or occlusion throughout.
level_5: Everything described for the 4-point level holds, and in addition: the left (rubber) strip stays fully intact throughout and returns to its original length and shape after release, while the right (plastic) strip develops a clear, visible crack (an open discontinuity spanning across its width) at some point in the sequence and never regains an unbroken, continuous form, with no ambiguity about which strip is undamaged and which is cracked, nor about its color, position, or action timing.

Scientific and Causal Correctness rubric:
level_1: Phenomenon contradicts subject knowledge: e.g., the rubber strip cracks or fails to recover its shape; the plastic strip fully recovers its original length with no crack ever appearing; both strips behave identically; or neither strip shows any lasting change after the stretch-release action.
level_2: At least one strip violates the expected material behavior: e.g., the rubber strip shows permanent elongation or tearing after release instead of full recovery; or the plastic strip shows elastic recoil/full recovery with no crack at any point; or the plastic strip's crack is not linked to the tensile stretching at all (e.g., it appears while the strip is sitting slack, unclamped, or otherwise unrelated to the applied strain).
level_3: The rubber strip visibly recovers its original length and shape after release (no permanent stretch, no tearing); the plastic strip develops at least one visible crack (a break in its surface continuity) while under tension (during the stretching motion or at the moment of maximum elongation); both outcomes are tied to the applied stretch, satisfying the core causal chain: stretch → rubber recovers upon release / plastic cracks under peak tensile strain.
level_4: Everything described for the 3-point level holds, and in addition: the rubber strip's recovery is complete (its length and shape in the final frame are indistinguishable from its pre-stretch state), the plastic strip's crack is irreversible (it stays open and visible through to the final frame, with no self-healing or reflattening), and no false phenomena occur (e.g., the rubber strip developing any crack, or the plastic strip bending without ever fracturing).
level_5: Everything described for the 4-point level holds, and in addition: the contrast between the two strips is unambiguous: in the final held frame, the rubber strip is continuous, taut, and undamaged at its original length, while the plastic strip displays a clearly defined crack spanning a visible portion of its width and remaining open, leaving zero doubt about which strip failed and which recovered.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal violation: one or both strips vanish and reappear at a different position, length, or clamp location between frames; the stretching or crack-forming action happens with no visible transition (the strip snaps instantly from unstretched to fully stretched, or from uncracked to cracked, within a single frame with no intermediate motion); a strip's material breaks apart into disconnected floating fragments rather than showing a bounded crack; or the scene's lighting abruptly shifts (e.g., sudden brightening, darkening, or a flash) with no visible cause mid-sequence.
level_2: Multiple moderate violations: e.g., the clamp holding either strip visibly slips or changes position between frames; the strip's outline flickers or blurs excessively during stretching; the stretching motion is noticeably jerky or discontinuous rather than a smooth elongation; or the crack on the plastic strip appears at one location in one frame and at a different location or width in a later frame without any visible propagation connecting them.
level_3: Both strips stay clamped at their original left/right positions throughout the video, with no unexplained shift in either clamp or strip location; the stretch-then-release motion is continuous, with no jumps, freezes, or instantaneous transitions; once the plastic strip's crack appears, it stays fixed at the same location and width for the remainder of the video; neither strip disintegrates, folds through itself, or visibly loses or gains volume.
level_4: Everything described for the 3-point level holds, and in addition: the stretching motion shows gradual, continuous elongation of both strips; the rubber strip's post-release recoil is continuous and decelerating rather than jumping straight to its rest length; the plastic strip's crack, once formed, does not partially close or reopen; the crack must not appear to happen before any stretching motion has occurred.
level_5: Everything described for the 4-point level holds, and in addition: both strips' motion reads as natural throughout: the rubber strip's stretch and recoil show believable acceleration and deceleration with no sudden freezing or sliding-without-deforming; the clamp stays visibly fixed and in continuous contact with both strips at all times; neither strip shows visible shaking or wobble along its edges; the plastic strip's thickness and the rubber strip's cross-section stay stable and proportionate throughout, without either strip appearing to thin, thicken, or warp beyond what the stretching motion itself would cause.