Domain: Natural Science — Physics
Target concept: Parallel spring

Video generation prompt: Two sets of spring balances are vertically suspended in parallel with one end fixed to the wall. The left set consists of a single spring balance, while the right set is composed of two spring balances of the same type as the left one, placed side by side and connected with their hooks merged. A metal weight of 500 g is suspended from the left spring balance, and another metal weight of 500 g is suspended from the right spring balance.

Evaluation guide:
(i) Target concept: Load sharing in parallel elastic elements under identical applied force.
Minimum mechanism: Identical spring constants, rigid wall fixation, perfect mechanical coupling at merged hook, negligible mass of springs, static equilibrium achieved before observation.
(ii)Storyline: Frame 1–2: Static wide shot showing wall, two vertical groups (left: one spring; right: two side-by-side springs with visibly fused hook), both weights hanging freely. Frame 3–8: Stable close-up or consistent framing revealing differential extension: left spring visibly more stretched; right springs equally stretched but less than left; no relative motion between right springs. Frame 9–10: Sustained static state confirming equilibrium: no oscillation, no drift, no detachment. Perspective must be frontal and fixed; no oblique angles obscuring side-by-side arrangement or hook merger; all critical objects fully in frame with no cropping.

Manual:
Experimental Procedure
1. Mount two vertical setups on a rigid wall: left uses one spring balance; right uses two identical spring balances placed side by side with hooks fully merged into one attachment point.
2. Suspend a 500 g metal weight from the left spring balance.
3. Suspend a 500 g metal weight from the merged hook of the right setup.
Observation of Experimental Phenomena
The left spring balance extends more than either individual spring balance on the right; the two right-side spring balances extend by equal amounts.
Summary of Experimental Principles
Parallel springs share load: total stiffness increases, so for same force, extension decreases per spring. Left side: k_total = k. Right side: k_total = 2k → same 500 g force produces half the extension per spring.

Prompt Grounding rubric:
level_1: No wall-mounted vertical suspension setup is visible: no spring balances appear in frame, no metal weights are shown, and there is no left-single/right-pair spatial arrangement of springs.
level_2: A wall-mounted vertical spring balance appears, but the left/right grouping specified in the prompt is not established: either only one spring balance is visible anywhere in the shot, the right side does not show two spring balances joined at a common hook, or no 500 g weight is clearly hanging from either side.
level_3: A rigid wall anchors two vertical groups: the left group is exactly one spring balance, the right group is exactly two spring balances mounted side by side with their lower hooks merged into a single attachment point; a 500 g metal weight hangs from the left spring balance and a 500 g metal weight hangs from the merged hook on the right; all objects read clearly as spring balances, metal weights, and a wall.
level_4: Building on the 3-point description, the two right-side spring balances are visibly the same model as the left spring balance (matching case size, coil diameter, and scale-face style), both weights are metallic, solid-looking, and match each other in size and shape, and the merged hook on the right is unambiguously a single shared coupling point where both right springs' lower ends and the weight's suspension loop meet.
level_5: Beyond the 4-point description, the left spring balance and each right-side spring balance show matching housing color, coil winding pattern, and printed scale markings; both weights are identically shaped cylindrical masses with matching surface finish; and the wall attachment for each spring balance is shown as a distinct, rigid bracket or bolted plate rather than a vague surface contact.

Scientific and Causal Correctness rubric:
level_1: No observable extension of any spring balance occurs in response to the weights; the left and right groups show no visible difference in behavior; there is no visible cause-and-effect between hanging the 500 g weights and any spring elongation.
level_2: At least one spring balance visibly extends, but not straight downward (e.g., a spring bows sideways), and/or there is no discernible difference between how far the left spring stretches and how far the right springs stretch; the two right springs stretch by clearly unequal amounts from each other.
level_3: Both the left spring and the two right springs visibly stretch downward once the weights are attached; the left spring's extension is clearly greater than either individual right spring's extension; the two right springs stretch by visibly equal amounts as each other; once reached, the extensions hold steady rather than continuing to grow or shrink.
level_4: Building on the 3-point description, each right spring's extension looks to be roughly half of the left spring's extension (clearly more than a small fraction of it, and clearly less than an amount close to the left's own extension), consistent with the right side's two springs jointly sharing the same 500 g load that the single left spring bears alone; neither right spring shows any reversal or renewed stretching/shrinking after the initial settling.
level_5: Beyond the 4-point description, the right springs' shared extension convincingly reads as about half the left spring's extension (not merely 'somewhat less,' and not close to equal to it), matching a total right-side stiffness twice the left's; the two right springs stay level with each other, with no visible tilt or gap opening between them, as they stretch; and the extension difference is sustained without any visible settling drift for the entire observed duration.

Spatiotemporal Consistency rubric:
level_1: A spring balance, the wall, or a weight vanishes or jumps to a new position between frames (e.g., a right-side spring disappears then reappears, or the merged hook detaches from a spring with no visible pulling motion); the lighting on the wall or weights changes abruptly from one frame to the next.
level_2: One brief glitch occurs, such as the merged hook on the right flickering out of view for a frame, one right-side spring shifting slightly relative to the other with no stretching motion to explain it, or the shadow cast by a weight jumping to a new direction while nothing else in the scene changes.
level_3: The wall stays in the same place throughout; the left spring balance and the two right spring balances remain attached to the wall and to the merged hook without any gap or break appearing; the two weights never disappear or jump position; any stretching of the springs looks like a smooth, gradual elongation rather than an instant jump to a new length.
level_4: Building on the 3-point description, the two right-side spring balances keep the same side-by-side spacing relative to each other for the entire sequence, the wall shows no shifting or sliding relative to the room behind it, and both weights hang straight down beneath their spring with no swinging or sideways drift.
level_5: Beyond the 4-point description, none of the springs, the wall, or the weights appear to stretch, bend, or warp out of their normal proportions in any frame; the visual depth relationship between the wall, the springs, and the weights stays consistent; and the camera's framing of the whole setup does not pan, tilt, zoom, or dolly at any point in the sequence.