Domain: Natural Science — Physics
Target concept: The interaction force between charges

Video generation prompt: Two identical lightweight spheres are suspended from the same support by insulating threads. A positively charged glass rod is brought into contact with the left sphere, and a negatively charged rubber (ebonite) rod is brought into contact with the right sphere. The two spheres are then brought close to each other, and their interaction is observed.

Evaluation guide:
(i) Target concept: Electrostatic attraction between oppositely charged objects via contact charging.
Minimum mechanism: Spheres must be conductive (to accept charge by conduction), lightweight (so electrostatic force dominates gravity), and suspended freely (to rotate/swing under net force); rods must carry net charge of specified sign; insulating threads prevent charge leakage to support.
(ii)Storyline: Frame 0–2: Static shot showing two spheres hanging vertically, threads taut, support visible, rods held away. Frame 2–4: Positive rod contacts left sphere; left sphere deflects *away* momentarily (repulsion during charging). Frame 4–6: Negative rod contacts right sphere; right sphere deflects *away* momentarily. Frame 6–10: Rods withdrawn; spheres swing *toward each other* and stabilize in mutual attraction. Viewpoint: fixed frontal close-up centered on suspension point; full visibility of both spheres, threads, rods, and support at all times; no occlusion.

Manual:
Experimental Procedure
1. Suspend two identical lightweight spheres side-by-side from a common rigid support using insulating threads.
2. Touch the left sphere with a positively charged glass rod; touch the right sphere with a negatively charged rubber (ebonite) rod.
3. Bring the two charged spheres close to each other without contact.
Observation of Experimental Phenomena
The two spheres attract each other and swing toward one another.
Summary of Experimental Principles
Like charges repel; unlike charges attract. Contact charging transfers charge: the left sphere acquires positive charge from the glass rod, the right sphere acquires negative charge from the rubber (ebonite) rod. The resulting opposite charges produce mutual electrostatic attraction.

Prompt Grounding rubric:
level_1: No suspended-sphere setup is shown at all (no two spheres, no insulating threads, no shared support, no rods), and no contact or proximity action occurs.
level_2: Part of the setup is visible, such as only one sphere or one thread, but at least two of the following are missing or unclear: the shared support, both spheres, the insulating threads, or the two rods; the sequence of contact followed by proximity isn't identifiable.
level_3: Both spheres, the insulating threads, the shared support, the glass rod, and the rubber (ebonite) rod are all present; the glass rod contacts the left sphere and the rubber rod contacts the right sphere, and the two spheres are then brought near each other afterward; the objects and the order of actions match the setup, regardless of what the spheres do once brought close.
level_4: Everything in level 3 holds, and in addition the spheres hang still and vertical before any contact, each rod touches its own sphere individually rather than both touching at once, the spheres stay suspended by their threads throughout, and both contact events finish before the spheres are brought near each other.
level_5: Every object looks the part: the spheres are round and light enough that the threads holding them barely sag, the threads look like a non-metallic material such as thread or fishing line rather than wire, the glass rod looks clear and smooth while the rubber rod looks matte and darker, and the shared support is rigid; nothing extra such as hands, labels, or arrows blocks or replaces any of these elements, and the camera stays fixed on the suspended spheres throughout.

Scientific and Causal Correctness rubric:
level_1: The spheres show no reaction to each other at all when brought close, or they move apart instead of together, or both behave as if they carry the same sign of charge, for instance both swinging away from each other.
level_2: The spheres move, but the direction is backwards for oppositely charged objects (for instance they drift apart instead of together when brought close), or one sphere reacts while the other stays put with no apparent reason, or a rod touches a sphere and the sphere shows no response to the contact at all.
level_3: Once both rods have finished touching their spheres, the two spheres visibly swing toward each other; either sphere may show a brief deflection away from its own charging rod during contact, but neither sphere shows attraction-driven motion toward the other sphere before both contacts are complete; the spheres keep their normal hanging posture throughout rather than falling or swinging wildly.
level_4: The spheres show no reaction at all before being touched; each sphere may show a brief deflection away from its own rod during contact, consistent with repulsion while charging, but neither sphere moves toward the other sphere as an attraction response until both contacts are finished, with no premature mutual approach and no back-and-forth wobble that a static charge wouldn't produce.
level_5: During contact, the left sphere visibly moves away from the glass rod and the right sphere visibly moves away from the rubber rod, consistent with each picking up charge from its own rod; afterward, as the two spheres are brought close, they lean toward each other steadily and by a similar amount on each side, settling with no lingering drift.

Spatiotemporal Consistency rubric:
level_1: The spheres jump from one position to another between shots, a thread vanishes and reappears, a rod appears in mid-air without a hand bringing it in, the support disappears for a moment, the lighting flickers or swings abruptly between bright and dark with no cause, or the clip cuts in a way that breaks the sense of continuous time.
level_2: A thread detaches and reattaches partway through, a sphere flips or spins with no apparent cause, a rod passes through a sphere rather than touching its surface, the background shifts position abruptly, or the motion is visibly jerky with more than a couple of noticeable skips.
level_3: The support and threads stay put and taut, the spheres hang vertically before any contact, the motion during contact and while being brought close looks smooth and physically reasonable rather than floating or suddenly speeding up, and nothing in the scene deforms, warps, or passes through anything else it shouldn't.
level_4: In addition, the thread length never visibly changes, each sphere's swing traces a smooth curved path rather than jumping between positions, motion never abruptly starts or stops, a rod never appears to pass through a sphere except at the instant of contact, and the camera angle stays fixed for the whole sequence.
level_5: The contact with the left sphere clearly finishes before the rod reaches the right sphere, both contacts are done before the spheres begin moving toward each other, and that final approach unfolds as one smooth, gradually accelerating motion with no pause, reversal, or repeated or skipped moment anywhere in the clip.