Domain: Natural Science — Physics
Target concept: Newton's cradle

Video generation prompt: A Newton's cradle consisting of five identical steel balls is displaced to an angle of 30° from the vertical, and then released. The collision and energy transfer process between the balls is observed.

Evaluation guide:
(i) Target concept: Elastic collision-mediated momentum transfer in a linear array of identical masses.
Minimum mechanism: All balls must be rigid, identical in mass and material; collisions must be near-perfectly elastic; suspension must constrain motion to a single plane with negligible friction/damping; initial displacement must involve only one ball.
(ii)Storyline: [Frame 0] Five balls at rest in contact, aligned horizontally; [Frame T1] Leftmost ball displaced laterally and held; [Frame T2] Ball released and accelerates downward along arc; [Frame T3] Leftmost ball contacts second ball: visible contact point and immediate deceleration; [Frame T4] Four middle balls remain stationary and mutually adjacent; [Frame T5] Rightmost ball begins upward arc with no delay after contact; [Visibility constraint] Fixed frontal/side viewpoint showing full linear alignment and unobstructed arc motion; no occlusion of ball contacts or wire attachments.

Manual:
Experimental Procedure
1. Arrange five identical steel balls in a straight line, suspended by thin vertical wires from a rigid horizontal bar.
2. Displace the leftmost ball 30° from vertical, hold briefly, then release freely.
Observation of Experimental Phenomena
— The released ball swings down and collides with the stationary line.
— Only the rightmost ball swings outward to approximately the same height; the four intermediate balls remain nearly motionless.
Summary of Experimental Principles
— Demonstrates conservation of momentum and kinetic energy in elastic collisions.
— In ideal identical-mass collisions, momentum transfers completely across a rigid chain, resulting in single-ball ejection.

Prompt Grounding rubric:
level_1: No Newton's cradle apparatus is visible: there are no five identical steel balls, no suspension wires, and no displace-then-release action shown at any point in the clip.
level_2: A suspended row of spheres appears, but the count is wrong (fewer or more than five balls), or the balls are not spherical or not matched in size/material, or they hang from something other than thin wires attached to a rigid horizontal bar; the displace-and-release action is missing, unclear, or applied to the wrong ball.
level_3: Exactly five identical, metallic gray-silver spheres of matching size hang in a single row, each on a thin wire from a common horizontal bar; the ball at one end of the row is pulled outward to an angle from vertical, held briefly, then let go so it swings back toward the row.
level_4: All conditions for score 3 are met, and additionally the ball that is pulled back and released is only the ball at one extreme end of the row (never a middle ball); the other four balls hang motionless and touching before release; no hand, clamp, ruler, or on-screen label remains visible during the swing-and-collision sequence.
level_5: All conditions for score 4 are met, and additionally the five balls hang at equal, touching spacing so their centers form a straight horizontal line at rest; the five wires are visibly straight, equal in length, and vertical at rest; the released ball swings within a single vertical plane without sideways tilt or twist; its release shows no visible push, flick, or nudge from an outside hand or tool.

Scientific and Causal Correctness rubric:
level_1: After release, no energy transfer to any other ball is visible: either every ball stays motionless, or more than one ball moves together at once instead of the motion passing along the row, or the outcome plainly breaks momentum/energy conservation, for example two balls swing outward together after only one ball was released and struck the row.
level_2: Exactly one ball swings down and strikes the row, but it fails to nearly stop on impact (it keeps moving into or past the row instead of arresting); or no ball at the far end swings outward at all; or the outward swing appears at the wrong ball (e.g., the second ball from the struck end swings out instead of the ball at the far end); or the balls between the struck end and the far end visibly jostle, rock, or separate instead of staying nearly still during the transfer.
level_3: After the released end ball swings down and strikes the row, exactly one ball, the one at the far end, swings outward while the released ball and the three balls between it and the far end stay nearly still against each other; the outward-swinging ball's peak height stays at or below the height from which the first ball was released (it never rises visibly higher than the release height), and it starts moving only once the released ball makes contact with the row, not before.
level_4: All conditions for score 3 are met, and additionally the released ball and the three balls between it and the far end stay in mutual contact throughout the impact and transfer rather than separating; the far-end ball's peak swing height is visibly close to (not clearly less than) the original release height; the released ball settles against the row afterward instead of rebounding into a second swing.
level_5: All conditions for score 4 are met, and additionally the released ball and the three balls between it and the far end show no visible rotation, sideways sway, or separation from one another at any point during the transfer; the far-end ball's outward swing begins only after the released ball has fully stopped against the row, with no overlap between the two motions; by the end of the clip every ball is either resting flush against its neighbors or swinging with a symmetric arc matching the release side, with none left drifting or spinning independently.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal break: one or more of the five balls vanish or appear out of nowhere between frames; a ball's size, shape, or color changes suddenly with no physical cause; a suspension wire snaps, disappears, or reattaches at a different point on the bar; two balls visibly pass through each other instead of colliding; or the scene's overall lighting abruptly brightens, darkens, or flashes with no visible cause partway through the clip.
level_2: Noticeable inconsistency: the number of visible balls changes from frame to frame (for example five balls become four and then five again); a wire visibly stretches, shrinks, or bends with no corresponding ball motion to explain it; a ball spins or rocks with no contact or force shown to cause it; the camera view or background shifts position mid-clip.
level_3: All five balls keep the same size, shape, color, and spacing relative to each other throughout the clip; each wire stays taut and vertical when its ball is at rest; the swinging ball's motion is continuous with no visible jump cuts or skipped positions; no ball overlaps or passes through another ball or wire.
level_4: All conditions for score 3 are met, and additionally each ball's metallic shine tracks its position smoothly as it moves, with no sudden flat or dark patches appearing on a ball's surface; the wires show no visible slack or sag whether their ball is at rest or mid-swing; the background stays fixed relative to the cradle frame with no drift suggesting camera movement; the swinging ball follows one smooth arc from release to contact with no sudden change in direction.
level_5: All conditions for score 4 are met, and additionally the released ball's arc and the far-end ball's outward arc stay within the same vertical plane with no sideways drift or twist; the balls show a consistent motion-blur direction during the fastest part of each swing, matching a single direction of travel; the ball centers and wire attachment points line up from one frame to the next with no visible skips; by the end of the clip the row of balls settles into a resting arrangement matching how it started, with no ball left out of alignment.