Domain: Natural Science — Physics
Target concept: Simple pendulum bob constrained by a rigid string

Video generation prompt: A metallic pendulum is fixed to a pivot on the ceiling by a rigid, thin string. It is pulled aside by a hand and released, then moves under the influence of gravity.

Evaluation guide:
(i) Target concept: Simple harmonic motion of an idealized simple pendulum under uniform gravitational field.
Minimum mechanism: Bob must be a rigid point-mass analog; string must be inextensible and massless (visually taut, straight, unchanging); pivot must be frictionless and immovable; gravity must act vertically downward (inferred from bob"s rest position and motion symmetry); no external forces (air resistance negligible, no magnetic/electrostatic effects).
(ii)Storyline: Frame 0–3: Static setup, bob hanging vertically at rest, string taut, pivot fixed to ceiling, hand approaching or contacting bob. Frame 4–5: Displacement phase, hand pulls bob laterally while maintaining contact; string tilts, bob rises slightly. Frame 6: Release instant, hand fully separates from bob; bob stationary at displaced position. Frame 7–10: Oscillation onset, bob accelerates downward and inward, traversing toward equilibrium, then continues past to opposite extreme where it momentarily stops (first turning point); motion remains planar, string stays straight, no energy injection.

Manual:
Experimental Procedure
1. A metallic spherical bob is suspended vertically from a fixed pivot on the ceiling by a rigid, thin string.
2. A hand grasps the bob and pulls it sideways to a displaced position.
3. The hand releases the bob — initiating motion.
Observation of Experimental Phenomena
The bob swings back and forth in a single vertical plane, reaching two turning points of equal height on either side before reversing direction; the string remains taut and straight at all times; because the pivot and string are treated as ideal (frictionless, massless), the swing's amplitude does not visibly decay over the observed motion.
Summary of Experimental Principles
A simple pendulum consists of a point mass (bob) constrained by an ideal rigid, massless string fixed at a pivot. Under gravity, displacement from equilibrium creates a restoring force proportional to displacement (small-angle approximation), resulting in periodic oscillatory motion.

Prompt Grounding rubric:
level_1: No metallic pendulum bob, no rigid thin string, and no ceiling pivot appear together; there is no hand contacting a bob and no release action; the scene shown is unrelated to a suspended pendulum setup (e.g., a liquid-filled vessel, a spinning wheel, or an object in unconstrained free-fall).
level_2: Some pendulum elements appear (the metallic bob, the thin string, the ceiling pivot, a hand, or a release gesture) but not all of them together, or their arrangement violates the prompt: e.g., the bob floats with no visible string, the string is missing, the hand never actually touches the bob, or the pivot sits on a table or floor instead of the ceiling.
level_3: The metallic bob, the rigid thin string, the ceiling pivot, a human hand touching the bob, and a release moment (the hand separating from the bob) are all present within one continuous shot; the bob hangs from the ceiling by the string, with the hand positioned beside it just before separation.
level_4: Everything required at level 3 holds, and additionally: the hand stays visible through the entire contact-to-release transition with no cut or occlusion; the string stays visibly connected from pivot to bob throughout; the bob is clearly still (no drift or pre-swing) in the instant before release; and the pivot is unmistakably mounted to the ceiling, not a wall bracket, a floor stand, or a free-floating point.
level_5: Everything required at level 4 holds, and additionally: the hand fully lets go, with no lingering contact or near-touch closer than roughly one bob-diameter; the string is visibly angled away from vertical at the moment of release (the bob is not hanging straight down when let go); and the bob, string, and pivot keep a consistent material appearance (metallic sheen, string thickness, pivot shape) from the first frame to the last, with no morphing or material swap.

Scientific and Causal Correctness rubric:
level_1: The bob's motion does not originate from gravity acting after release: it moves upward on its own, floats, spins by itself, speeds up for no reason, or follows a non-swinging path (a straight line, a spiral, random jitter) with no visible link between the hand's release and the start of motion.
level_2: The bob swings, but the physics breaks down somewhere: it passes straight through the pivot, the string visibly stretches, the bob changes shape, color, or opacity mid-swing, motion starts before the hand lets go, the swing keeps a constant speed with no slowdown, or the bob never actually comes to a stop at either extreme.
level_3: After release, the bob swings back and forth; the motion begins only once the hand has separated from it; the bob comes to a visible, momentary stop at each of the two extremes (left and right) before reversing; the string stays taut throughout, never slack or sagging; and no outside push, gust, or magnetic-looking force is visible influencing the swing.
level_4: Everything required at level 3 holds, and additionally: the whole swing stays within a single vertical plane, with no sideways wobble or twist out of that plane; the two turning-point heights sit level with each other relative to the pivot, matching the symmetric swing expected of an ideal, frictionless pivot and massless string; the bob passes directly beneath the pivot only at the bottom of each swing; and there is no sudden speed-up, bounce, or added energy visible at either turning point.
level_5: Everything required at level 4 holds, and additionally: from release to the first opposite extreme, the bob's speed tapers off smoothly with no stutter or overshoot before it stops; the string stays straight, with no visible bend or kink at any point in the swing; the bob's metallic surface keeps a consistent reflective look at every position relative to the room's light; and each direction reversal happens only at a clearly held, momentary stop, never blurred over in a way that hides the stillness.

Spatiotemporal Consistency rubric:
level_1: There is a major continuity break: the bob jumps between positions with no motion carrying it there; the string disconnects from the pivot or bob and reconnects; the pivot's location shifts to a different spot; the hand vanishes and reappears; the room's lighting or shadows behave as if a different light source or time of day suddenly took over; or the video freezes or drops frames for a visibly long stretch.
level_2: Several moderate breaks appear: the bob blinks in and out of view; the string disappears momentarily or bends/warps unnaturally; the hand occludes the bob and then reappears in a noticeably different pose than before the occlusion; the pivot visibly slides sideways by more than about a quarter of the frame width; the room's lighting brightness or direction changes partway through with no visible cause (e.g., a lamp or window appearing that wasn't there before); or the swing stutters with three or more visible skips or judders.
level_3: Only one minor issue is present: either (a) the hand briefly covers less than about a third of the bob's area during release, (b) the shadow cast by the bob shifts slightly in position without changing shape or size, (c) the string shows a single-frame kink without ever disconnecting, or (d) the camera drifts by less than about 5% of the frame width, but there is no jump in the bob's position, no disconnection of the string from pivot or bob, and the swing stays smooth and continuous.
level_4: Everything required at level 3 holds, and additionally: nothing ever hides the pivot, the string's anchor point, or the bob's full outline; the room lighting never suddenly shifts in brightness, color, or direction (no lamp switching on or off, no new light source appearing); the string keeps a consistent thickness from pivot to bob in every frame; and the bob's position changes smoothly, with no jump-cut in its path.
level_5: Everything required at level 4 holds, and additionally: the camera viewpoint holds steady, with no visible drift, pan, or zoom relative to the room's fixed background (walls, ceiling, furniture); the bob's outline stays clear enough that its shape and edges remain identifiable even while swinging; the string shows no visible flicker in thickness or position from one frame to the next; the pivot visibly stays fixed at the same spot on the ceiling for the entire video; and the shadow cast by the bob moves in a way that stays physically consistent with the bob's own position throughout the swing.