Domain: Natural Science — Physics
Target concept: Conservation of Angular Momentum: A person sitting on a rotating chair brings their arms close and extends them.

Video generation prompt: A person sitting on a freely rotatable stool in the laboratory holds dumbbells and rotates, first bringing the arms close to the chest, then extending the arms outward without touching the ground.

Evaluation guide:
(i) Target concept: Conservation of angular momentum in a closed rotational system.
Minimum mechanism: Person + stool + dumbbells must form an isolated rotational system; no external torque (feet off ground, no contact with surroundings), rotation axis fixed and vertical, mass distribution changes solely via arm movement.
(ii)Storyline: Phase 1 (Start): Person seated, arms at shoulder height, stool rotating at baseline speed. Phase 2 (Close): Arms move symmetrically inward → rotational inertia decreases → rotation accelerates (visibly tighter/faster turns). Phase 3 (Extend): Arms move symmetrically outward → rotational inertia increases → rotation decelerates (visibly wider/slower turns). Perspective constraint: Fixed frontal or 3/4 view showing full upper body, stool base, and rotation path; no occlusion of arms, dumbbells, or stool axis; lighting enables clear tracking of rotational motion against background.

Manual:
Experimental Procedure
1. Person sits upright on freely rotatable stool, holding one dumbbell in each hand at shoulder height.
2. Person pulls both arms inward symmetrically until dumbbells touch chest.
3. Person extends both arms outward horizontally to full reach.
Observation of Experimental Phenomena
Stool rotates faster when arms are pulled inward; rotation visibly slows when arms are extended outward.
Summary of Experimental Principles
Conservation of Angular Momentum: With no external torque, reducing rotational inertia (by bringing mass closer to axis) increases angular velocity; increasing inertia (by extending mass outward) decreases angular velocity.

Prompt Grounding rubric:
level_1: No rotating stool is shown; no person is seated; no dumbbells appear; there is no arm movement sequence; the scene shows something unrelated (e.g., a static desk or an outdoor scene).
level_2: A seated person and a stool appear, but the stool is not free to rotate (e.g., it is an office chair with its wheels visibly locked, or sits on a surface that would prevent turning); the dumbbells are missing or replaced by unrelated objects (e.g., books or bottles); the arms stay still or move without any clear inward-then-outward pattern.
level_3: The person sits on a stool with a visible swivel base or unobstructed casters; two dumbbells are held, one in each hand; the arms move in two distinct, temporally separated phases: first drawn in toward the chest, then extended back out away from the torso; both phases are fully visible on screen.
level_4: All of 3-score, plus the stool keeps turning in the same direction throughout the entire sequence, through both arm phases, without stopping and restarting; the person's feet stay off the floor the whole time, with no foot ever touching the ground.
level_5: All of 4-score, plus the two dumbbells are identical in size, shape, and color; the left and right arms move together and mirror each other in timing and path; no extra objects, occlusions, or camera cuts interrupt the single continuous take from start to finish.

Scientific and Causal Correctness rubric:
level_1: There is no link between arm position and rotation speed: the stool's turning rate stays constant regardless of arm position, or changes randomly; when the arms move outward the stool does not slow down, and when the arms move inward it does not speed up. The behavior contradicts conservation of angular momentum.
level_2: The stool's rotation speed does change with arm position, but in the wrong direction (e.g., it slows when the arms come in and speeds up when they extend), or the speed only changes during one of the two phases while staying constant during the other.
level_3: The stool visibly turns faster once the arms are drawn in toward the chest, and visibly turns slower once the arms are extended back out; both speed changes are noticeable by eye, such as the stool completing visibly more or fewer full turns in the same stretch of video during each phase.
level_4: All of 3-score, plus the speed change within each phase runs in one steady direction: the rotation keeps smoothly speeding up throughout the whole arm-closing phase and keeps smoothly slowing down throughout the whole arm-extending phase, without reversing or stuttering partway through; the stool's spin stays centered on its own axis with no visible wobble or tilt while the speed is changing.
level_5: All of 4-score, plus the size of the speed change looks clearly proportional by eye: the fastest rotation (arms fully in) is noticeably faster than the slowest rotation (arms fully out), not just marginally different; the rotational motion is never hidden by motion blur, frame drops, or a background so plain that the turning can't be judged by eye.

Spatiotemporal Consistency rubric:
level_1: The person or stool jumps to a different position or pose between frames with no motion in between (e.g., arms shown fully extended in one frame and fully drawn in on the very next); the stool's base blinks out of frame and comes back without ever having genuinely moved off-screen; the lighting suddenly flashes or cuts to black with no cause; a body part appears to stretch or bend in an unnatural way.
level_2: The dumbbells briefly pass behind the torso and never come back into view; the stool's base drops out of frame for a moment as the camera angle appears to shift and then returns; the shadows appear to point a different way for part of the clip even though nothing else suggests the light moved; the rotation looks jerky, freezing or stuttering at least twice.
level_3: The stool's base stays visible and in contact with the floor the whole time; the person's seated posture stays steady, without sliding, rising, or sinking in the seat; the arms move smoothly with no jump in position; the shadow cast by the person and stool keeps pointing the same way and staying about the same darkness for the whole clip; the rotation looks smooth and centered on the stool's axis.
level_4: All of 3-score, plus the camera itself never pans, tilts, or zooms; the person's head and torso stay in about the same part of the frame throughout; the dumbbells stay on screen at every moment; the stool's spin axis stays vertical with no visible lean or wobble.
level_5: All of 4-score, plus no motion blur ever hides the outline of an arm or dumbbell; the turning motion never freezes into a stutter that makes it look like a strobe; no part of the stool, person, or dumbbells appears to stretch or warp; the arms and dumbbells in the foreground move in a way that stays visually consistent with the wall or floor behind them, with no mismatched sense of depth.