Domain: Natural Science — Physics
Target concept: Add the salt powder to the saturated salt solution, stir and confirm that the salt does not dissolve and precipitates completely at the bottom of the container.

Video generation prompt: Use a transparent cup containing saturated salt water. Add a small amount of solid salt powder to the solution. Stir gently with a glass rod for a few seconds, then stop stirring and keep the cup still, to demonstrate the result of adding excess solute to a saturated solution.

Evaluation guide:
(i) Target concept: Saturation as a dynamic equilibrium state where dissolution rate equals crystallization rate in a closed system at constant temperature.
Minimum mechanism: Liquid must be truly saturated (no net dissolution possible), solute must be identical in chemical identity and phase (solid NaCl), container must be inert and transparent, temperature must remain effectively constant (no visible thermal convection), and observation time must exceed settling time for gravity-driven precipitation.
(ii)Storyline: [Phase 1: Baseline] Static shot of an upright transparent cup holding clear liquid, its surface calm with no solids visible. → [Phase 2: Salt Addition] A small amount of dry salt powder is deposited onto the liquid surface as a localized patch, without splashing or dispersing. → [Phase 3: Stirring] A glass rod enters the liquid, performs one smooth circular stir without lifting out or scraping the cup bottom, then fully withdraws. → [Phase 4: Settling & Stillness] The cup remains completely still; the salt particles move downward, briefly speed up, then slow to a full stop at the bottom of the cup; the liquid above stays clear and undisturbed, with no further movement at the surface or within the liquid.

Manual:
Experimental Procedure
1. Place transparent cup filled with clear saturated salt water at center of frame.
2. Add small amount of white solid salt powder onto liquid surface.
3. Insert glass rod into liquid and stir gently for one continuous circular motion.
4. Withdraw rod fully and hold cup motionless.
Observation of Experimental Phenomena
After stirring stops, undissolved white granular salt precipitates and remains fully settled at the bottom; liquid above stays transparent and clear.
Summary of Experimental Principles
A saturated solution cannot dissolve additional solute; excess salt remains as solid phase, confirming dynamic equilibrium between dissolution and crystallization.

Prompt Grounding rubric:
level_1: No transparent cup is shown; no clear salt-water liquid is visible in it; no white salt powder is added; no glass rod appears; no stirring action takes place; no stillness period is shown afterward.
level_2: Some elements appear (a cup, a liquid, a white granular substance, or a rod-like object), but not in the right roles: for example the cup is opaque instead of transparent, or the rod is never used to stir, or the stirring and the after-stillness moment are missing or swapped in order.
level_3: A transparent cup holding a clear liquid is visible; white solid salt powder is added onto the liquid; a glass rod enters and stirs the liquid for at least one visible full circular pass; the rod is then withdrawn or held still, and the cup itself stays motionless for the rest of the clip.
level_4: All 3-point requirements are met, and in addition: the cup stands upright and centered in frame; the salt powder is added before the stirring begins, not after or during; the rod only stirs while it is inside the liquid; the rod is fully out of the liquid, or held motionless above it, before the still phase begins; no unrelated action (e.g., a hand pouring something else in, or re-entering after the rod was withdrawn) interrupts the sequence.
level_5: All 4-point requirements are met, and in addition: the salt powder lands as one localized patch on the liquid surface rather than scattering across it before stirring starts; the stirring stays gentle and fully inside the cup with no splashing or the rod lifting partway out mid-stir; once stirring ends, the rod is either completely clear of the liquid or held steady above it; the cup shows no shake, tilt, or shift in position from that point until the clip ends; the steps (adding salt, stirring, withdrawing the rod, and stillness) read as one continuous, uninterrupted sequence.

Scientific and Causal Correctness rubric:
level_1: The liquid turns colored, cloudy, or gel-like; the added salt powder fully dissolves during or after stirring, leaving no visible residue; no solid settles anywhere in the cup; there is no visible difference between the liquid before and after the salt was added.
level_2: The liquid stays clear, but no solid residue remains once stirring stops; or solid is visible only while the rod is stirring and disappears the instant stirring ends; or particles form but stay suspended in the liquid without ever reaching the bottom, or appear as a diffuse haze instead of distinct settled grains.
level_3: After stirring stops and the cup is still, visibly undissolved white grains sit at the bottom of the cup; the liquid above those grains stays clear with no cloudiness; the salt that was added does not dissolve further during the stillness period.
level_4: All 3-point requirements are met, and in addition: the white grains are found only at the bottom, with none floating on the surface or suspended partway up; the liquid above looks just as clear as it did before the salt was added, with no new haze; neither the liquid nor the grains change color; the grains stay granular rather than melting together into a film or forming a dissolving halo.
level_5: All 4-point requirements are met, and in addition: the grains only begin settling after the rod stops stirring, with no settling visible while the rod is still moving; once settled, the grains stay completely still for the rest of the clip; no leftover salt visibly clings to the rod or to the cup wall above the bottom region; the boundary between the settled grains and the clear liquid above stays sharp and steady, with no swirling, re-suspension, or curved meniscus distortion suggesting further mixing.

Spatiotemporal Consistency rubric:
level_1: The cup jumps to a different position between one moment and the next with no motion connecting them; the liquid surface suddenly changes level or shape with no visible cause; the salt powder or the rod appears or disappears out of nowhere; the lighting on the scene changes abruptly with no explanation; the cup tips or rotates sharply for no physical reason.
level_2: The cup shifts sideways by roughly its own width or more; the rod appears and disappears inconsistently as if teleporting in and out of the shot; the liquid level rises or falls without anything being poured in or taken out; salt particles blink in and out of view; the lighting or shadows shift more than once without explanation; the stirring or settling motion looks clearly choppy, with visible stalls or skips in the movement.
level_3: The cup wobbles slightly during the still phase, or the rod trembles a bit while stirring, or the shadow shifts slightly once, but nothing passes through anything it shouldn't (for instance the rod never appears to pass through the cup wall), and these small imperfections are the only issues visible.
level_4: All motion looks physically believable and spatially consistent: the rod moves along a natural hand-driven path; the cup stays fixed in the frame with no drifting or turning; the liquid surface dips and smooths back out believably during stirring; the salt particles sink in one continuous downward motion without jumping backward or teleporting.
level_5: No spatiotemporal flaws are visible: the cup's position, angle, and size look completely steady across the still phase, with no drift the eye can detect; the stirring motion is smooth and continuous with no sudden speed changes or unnatural pauses; the particles' settling looks uninterrupted and continuous from when they start sinking to when they come to rest; the lighting, focus, and exposure look consistent throughout with no visible flicker.