Domain: Natural Science — Physics
Target concept: Weightlessness

Video generation prompt: An experimenter holds a spring scale inside an elevator, with a 500g mass suspended beneath the scale; the elevator accelerates rapidly downward, and the change in the scale's reading is observed;

Evaluation guide:
(i) Target concept: Apparent weight reduction due to downward inertial acceleration in a non-inertial frame.
Minimum mechanism: Elevator must accelerate downward (not merely move downward at constant velocity); scale must measure tension force in real time; mass must remain mechanically coupled to scale (no detachment or free fall); reading change must reflect reduced tension, not instrument error or drift.
(ii)Storyline: [Frame 1–2] Static baseline: elevator stationary, scale shows ~5N (or needle at calibrated position), mass hanging vertically. [Frame 3–5] Acceleration onset: visual descent cue appears (e.g., floor indicator changes, cable motion begins), scale reading immediately begins decreasing. [Frame 6–8] Accelerated descent: reading stabilizes at lower value, mass remains taut and aligned. [Frame 9–10] (Optional) Deceleration/stop: reading rises back toward baseline; but at minimum, decrease must occur *only* during active downward acceleration phase. Perspective: fixed medium-close shot centered on scale–mass system, full visibility of scale face and suspension point, no occlusion.

Manual:
Experimental Procedure
1. Experimenter stands inside elevator cabin, holding a spring scale by its top handle.
2. A 500g mass is hung from the scale's bottom hook.
3. Elevator accelerates rapidly downward.
Observation of Experimental Phenomena
The spring scale reading decreases during downward acceleration, while the mass remains suspended and taut.
Summary of Experimental Principles
Under downward acceleration, the apparent weight of the mass decreases because the net force on the mass is mg − ma = m(g − a), reducing tension in the spring — demonstrating weightlessness as a local reduction in the spring's tension force, per Newton's second law.

Prompt Grounding rubric:
level_1: No elevator cabin is shown, no spring scale appears, no 500 g mass is suspended beneath it, and no experimenter's hand holds the scale; there is also no visual cue of downward acceleration (no descending floor indicator, no downward-streaking background, no cable movement).
level_2: An elevator interior appears but the scale and the 500 g mass are not both present, or the scale is shown without a hand holding it, or the only sign of downward acceleration is a caption or spoken line rather than anything visible in the shot.
level_3: The elevator interior, the experimenter's hand gripping the scale, and the 500 g mass hanging from the scale's hook are all visible together, arranged in the correct order (hand above scale above mass), and the elevator's downward acceleration is shown through a visible cue such as a descending floor number, downward-streaking ceiling lights, or cable motion.
level_4: Everything in the score 3 description holds, and in addition the scale's face (dial or digital readout) stays fully visible and readable for the whole sequence, the mass stays continuously attached to the hook without swinging out of frame, the hand's grip on the scale handle stays steady without re-gripping or slipping, and nothing else in the shot blocks the view of the scale-mass assembly.
level_5: Everything in the score 4 description holds, and in addition the camera keeps the scale-mass system centered and unobstructed in frame from the first shot of the static baseline through the end of the sequence, with the hook, the scale housing, and the hanging mass all visible without cropping, zooming, or panning away at any point.

Scientific and Causal Correctness rubric:
level_1: The scale's reading rises or stays the same while the elevator visibly accelerates downward, or it drops while the elevator instead accelerates upward, or the 500 g mass separates from the hook (or appears to float) while the scale still shows a nonzero reading, or the scale sits at zero while the mass hangs motionless and taut. Any of these directly contradicts the tension reduction expected here from Newton's second law.
level_2: The reading does fall, but its timing is off: it starts dropping before the elevator shows any downward acceleration, or only after the elevator has already stopped; or the reading touches zero at some point even though the mass is still hanging taut on the hook; or the hook goes visibly slack (mass appears to be in free fall relative to the scale) while the display still shows a nonzero value.
level_3: The reading visibly decreases while the elevator's downward acceleration is on screen, the mass stays taut on the hook the entire time (no slack, no floating away from the hook), and no frame shows the mass hanging taut while the display is inconsistent with that (e.g., reading at zero or unchanged).
level_4: Everything in the score 3 description holds, and in addition the size of the drop looks physically reasonable for reduced tension: the reading ends up clearly below the static baseline (for example, moving from near 5 N down toward roughly half that) rather than staying near baseline or hitting zero, and the mass never appears to push upward into the scale housing.
level_5: Everything in the score 4 description holds, and in addition the reading begins falling right when the downward acceleration becomes visible (no noticeable lag or head start), holds steady at the lower value through the constant-acceleration portion without erratic jumps, and, if the elevator is shown decelerating or stopping, the reading climbs back toward the original baseline in step with that slowdown.

Spatiotemporal Consistency rubric:
level_1: The scale, the mass, or the experimenter's hand blinks out of one frame and shows up in a new spot in the next, with nothing shown moving it there; the elevator cabin's proportions change abruptly (e.g., the ceiling height jumps between shots) or its walls visibly tear or the scale bends in a way metal cannot; the lighting suddenly shifts character (e.g., from daylight to night) in a single frame with no visible cause; the mass jumps from one hanging position to another with no visible path between them; or the shadow the mass casts switches sides with nothing in the shot (light source, camera) moving to explain it.
level_2: The scale or the mass drops out of view for two or more consecutive frames before reappearing; the elevator cabin's walls visibly stretch, shear, or bend between frames; or the mass's shadow swings to the opposite side of the floor without any corresponding movement of the camera or a light fixture in the shot.
level_3: The hand, scale, and mass keep a steady, continuous spatial arrangement (hand above scale above mass) throughout; any motion blur present points downward, matching the elevator's descent rather than sideways or upward; and the shadow the hanging mass casts on the cabin floor shifts only in proportion to the mass's own downward travel, not on its own.
level_4: Everything in the score 3 description holds, and in addition the mass never slides sideways off the hook's centerline as the clip progresses, the mass and the scale housing never appear to pass through each other, and the camera's framing stays fixed with no unexplained zoom, pan, or rotation.
level_5: Everything in the score 4 description holds, and in addition any swinging of the mass damps out smoothly at the start and end of the acceleration rather than continuing throughout the descent, the scale's needle or digits change position smoothly rather than jumping between values, and no frame shows a doubled or trailing copy of the scale or mass.