Domain: Natural Science — Physics
Target concept: The wax-pin experiment with one-end heating on metal and glass rods

Video generation prompt: A horizontal metal rod is placed on the left, and a glass rod is placed on the right, with metal needles fixed to both rods using wax; the ends of both rods are simultaneously heated by a stable flame.

Evaluation guide:
(i) Target concept: Differential thermal conductivity between metal and glass drives sequential wax-melting and needle detachment.
Minimum mechanism: Wax must remain solid until heated above its melting point; heat transfer rate must differ significantly between rod materials; needle detachment requires localized wax phase change (solid→liquid), not rod deformation or adhesive failure; gravity must act uniformly to cause downward fall.
(ii)Storyline: Frame 1–2: Static shot showing left metal rod + right glass rod, both horizontal, each with single wax-fixed needle near center. Frame 3–4: Flame appears simultaneously at outer ends (left end of metal rod, right end of glass rod). Frame 5–7: Metal-rod needle detaches and begins smooth downward fall. Frame 8–10: Glass-rod needle remains fully attached and motionless while metal-rod needle completes fall; no detachment of glass-rod needle occurs within video duration. Perspective: Fixed frontal view, full rods visible, no occlusion, consistent lighting, no camera motion.

Manual:
Experimental Procedure
1. Place a horizontal metal rod on the left and a horizontal glass rod on the right, aligned side-by-side.
2. Fix one metal needle to each rod using wax — one on the metal rod, one on the glass rod.
3. Simultaneously apply a stable flame to the outer end of each rod (left end of metal rod, right end of glass rod).
Observation of Experimental Phenomena
The needle on the metal rod falls first; the needle on the glass rod remains attached longer and falls later.
Summary of Experimental Principles
Metals conduct heat faster than glass; thus, heat travels more rapidly along the metal rod, melting the wax sooner and causing earlier needle detachment.

Prompt Grounding rubric:
level_1: No pair of horizontal rods is shown, or the rods are not arranged with the metal rod on the left and the glass rod on the right; wax-fixed needles are missing from one or both rods; no flame is shown touching either rod's end; the flame does not touch both rod ends at the same time.
level_2: The metal rod and glass rod are shown side by side, but their left/right placement is swapped (metal on the right, glass on the left); or a wax-fixed needle is attached to only one of the two rods; or the flame touches only one rod's end while the other end stays untouched; or the flame appears before both rods and needles are fully in position.
level_3: The metal rod sits on the left and the glass rod on the right, both horizontal and roughly level with each other; a needle fixed with wax is visible on each rod; a single, steady flame touches the outer end of each rod (the left end of the metal rod and the right end of the glass rod) at the same time.
level_4: Everything required at level 3 is shown, plus: both rods stay horizontal and in place for the whole clip; each needle is clearly visible as a separate object fixed onto its rod by wax before the flame appears; the flame stays in continuous contact with both rod ends without flickering out or drifting away partway through.
level_5: Everything required at level 4 is shown, plus: the flame on each side looks similar in size and steadiness to the other; the two rods are parallel and sit at the same height; each needle is attached at a matching position along its rod (e.g., both near the rod's midpoint); nothing blocks the view of either rod, either needle, or the flame at any point.

Scientific and Causal Correctness rubric:
level_1: No needle falls at all; or both needles fall at the same time; or a needle falls before the flame touches its rod; or a needle detaches without falling (e.g., it slides off sideways, floats, or disappears instead of dropping); or a rod visibly melts, bends, or changes color in a way that has nothing to do with simple heat conduction.
level_2: Only the glass-rod needle falls, or it falls before the metal-rod needle does, while the metal-rod needle stays attached; or a needle's fall happens in a non-gravitational or discontinuous way (e.g., it jumps between frames, appears as a jump-cut, or drifts down unnaturally slowly); or wax on a rod visibly softens or drips without any needle actually detaching.
level_3: The metal-rod needle detaches and falls before any change is visible in the glass-rod needle; the metal-rod needle's fall follows a continuous downward path; no other unrelated change occurs on either rod (no wax dripping from the glass side, no rod bending, no unrelated color shift).
level_4: Everything required at level 3 holds, plus: the metal-rod needle's detachment clearly begins before the glass-rod needle shows any sign of loosening; the metal-rod needle's fall is smooth and continuous rather than jerky; the wax on the glass rod stays visibly solid and unchanged for as long as the clip shows it, and its needle stays exactly in place.
level_5: Everything required at level 4 holds, plus: the metal-rod needle fully detaches and falls while the glass-rod needle stays completely attached and motionless for the entire clip, including after the metal-rod needle has finished falling or left the frame; no wax residue or distortion is visible where the metal needle detached; the glass-rod needle shows no sign of falling, loosening, or being disturbed at any point.

Spatiotemporal Consistency rubric:
level_1: The metal rod or the glass rod jumps to a new position or angle between shots with no movement shown causing it; the flame appears or disappears instantly instead of visibly igniting or going out; a needle is present in one frame and simply gone (or back) in the next with no motion connecting the two states; the overall brightness or shadow pattern on the rods changes suddenly partway through with no visible cause.
level_2: The apparent length of a rod changes noticeably between shots; a falling needle's apparent size changes inconsistently as it drops; the flame's size or shape changes abruptly rather than flickering the way a real flame would; elements of the background shift position or warp during the sequence.
level_3: The metal rod, glass rod, flame, and both needles keep the same size and the same position relative to one another throughout the clip; the flame stays anchored at the rod ends it is heating; each needle stays fixed to its rod until the moment it detaches; any motion, such as a needle falling, proceeds smoothly in one direction without floating upward or reversing.
level_4: Everything required at level 3 holds, plus: there is no jitter, warping, or distortion of the rods, needles, or flame from frame to frame; there is no sudden jump in overall brightness or shadowing across the clip; the video shows no frozen or skipped moments — the falling needle's motion proceeds without gaps; the edges of the rods and needles stay sharp and stable rather than blurring in and out.
level_5: Everything required at level 4 holds, plus: the camera does not pan, tilt, or zoom at any point; the relative depth and overlap between the rods/needles and the background stay consistent throughout; the foreground objects and background move together with no visible mismatch; any motion blur on the falling needle is consistent in direction and does not obscure which needle is falling.