Domain: Natural Science — Physics
Target concept: The process of transition from nucleate boiling to film boiling of a water droplet on a continuously heated metal surface

Video generation prompt: Place a clean metal plate on the heating element, steadily increase its temperature, and drop the same volume of water at fixed time intervals onto the same location.

Evaluation guide:
(i) Target concept: Leidenfrost effect as the macroscopic manifestation of the nucleate-to-film boiling transition under steady surface heating.
Minimum mechanism: Liquid water must contact a solid surface significantly hotter than its boiling point; sufficient thermal inertia in the solid to sustain high local temperature between droplet impacts; vapor generation rate at interface must exceed condensation rate to form stable insulating layer.
(ii)Storyline: [Phase 1: Baseline] Metal plate appears cool/ambient; first droplet impacts, spreads, vibrates, emits turbulent steam, fully wets surface, evaporates in <1 sec. [Phase 2: Transition] Plate surface subtly darkens near center; second/third droplet shows reduced spreading, shorter steam duration, faster recoil. [Phase 3: Film onset] Fourth/fifth droplet makes no wetting contact: hovers 0.5–2 mm above surface, moves freely, retains perfect sphere, zero steam, mirror-like surface reflection. [Visibility constraint] Fixed overhead view centered on impact zone; plate fills ≥60% of frame width; droplet release point is out-of-frame top-center; no occlusion of droplet flight path or plate surface.

Manual:
Experimental Procedure
1. Place clean, flat metal plate directly on heating element.
2. Power on heater and allow plate temperature to rise steadily (no manual adjustment).
3. At fixed time intervals, drop identical-volume water droplets onto the exact same location on the plate surface.
Observation of Experimental Phenomena
- Early droplets spread rapidly, sizzle, emit steam, and evaporate quickly (nucleate boiling).
- Later droplets levitate, skitter smoothly, remain spherical, emit no steam, and persist longer (film boiling / Leidenfrost effect).
Summary of Experimental Principles
Transition from nucleate boiling to film boiling occurs as surface temperature exceeds the Leidenfrost point (~200°C for water on steel); vapor layer insulates droplet, reducing heat transfer and enabling sustained levitation.

Prompt Grounding rubric:
level_1: No metal plate is shown, no heating element is shown, and no water droplet is ever dropped onto a plate; there's no hint of any of the prompt's actions: placing the plate on a heater, letting its temperature rise, or dropping same-size water drops onto one spot at even intervals.
level_2: A metal plate and a heating element both appear, but the plate is never actually resting on the heater; water drops appear, but they land at different spots on the plate rather than the same spot, or the gaps between drops are clearly uneven (e.g., two drops in quick succession, then a long pause); nothing on screen hints that the plate is getting hotter over time.
level_3: The plate sits on the heating element; at least three water drops of matching size fall onto the same visible spot on the plate; the pauses between successive drops look roughly equal in length; nothing in the clip suggests the plate cools down or resets partway through (no drop behaves as if the surface got colder again after being hot).
level_4: Everything in level 3 holds, plus: every drop is released from the same height and falls straight down rather than at an angle or with a splash beforehand; the plate itself never shifts, tilts, or leaves the frame; no unrelated props (tongs, thermometers, a second plate) appear; the camera holds one fixed framing on the impact area for the whole clip.
level_5: Everything in level 4 holds, plus: each drop can be seen landing within the same small target area on the plate, with no visible drift of the impact point from the first drop to the last; the plate's edges stay crisp and steady rather than swimming, doubling, or blurring; every drop appears to fall from the same point in the air above the plate; no drop and no part of the plate flickers, vanishes, or jumps to a different spot between moments.

Scientific and Causal Correctness rubric:
level_1: The drops never show a believable boiling-transition sequence at all: for example, every drop disappears the instant it touches the plate, or every drop just sits there and slowly evaporates the same way no matter when it was dropped, with no visible difference between the very first drop and the very last.
level_2: Some difference shows up between drops, but it doesn't track a nucleate-to-film progression: e.g., a middle drop spreads and sizzles just as much as an earlier one, or the amount of visible steam and spreading doesn't shrink as the sequence goes on; early and late drops look interchangeable.
level_3: The early drops clearly spread out across the plate, sizzle with visible agitation, throw off steam, and disappear quickly (nucleate boiling); the later drops clearly ride above the surface as near-perfect spheres, glide around with little resistance, and give off almost no steam (film boiling / Leidenfrost behavior); this shift happens in the same order the drops are released, not scrambled.
level_4: Everything in level 3 holds, plus: once a drop shows the floating, steam-free behavior, no later drop reverts to spreading and sizzling; every floating drop keeps its round shape and glides smoothly rather than merging with, or splitting off from, another drop; steam only ever appears during the early sizzling drops, never during the later floating ones.
level_5: Everything in level 4 holds, plus: every single drop can be confidently placed into one of two categories just by watching it: nucleate boiling shows spreading, vigorous bubbling, visible steam, and full contact with the plate all together; film boiling shows a floating sphere, smooth gliding, no steam, and a mirror-like sheen all together, with no drop showing a confusing mix of the two sets of cues.

Spatiotemporal Consistency rubric:
level_1: Major breaks in continuity: the plate jumps to a different position or angle between one moment and the next; a droplet appears already in mid-air or already on the plate with no visible fall leading up to it; the lighting swings from bright to dark (or the reverse) between consecutive moments; the plate's surface changes shape or texture with no explanation; the camera angle cuts between a top-down and a side view partway through the clip.
level_2: Noticeable but less severe problems: the plate tilts or spins with no physical cause; a droplet's fall is visible near the top and then it's suddenly already landed, skipping the middle of the fall; a shadow shifts position or strength in a way that doesn't match a single fixed light source; background elements flicker or warp; an edge of the plate blinks out for a moment and then reappears.
level_3: Small, only occasionally noticeable issues: a drop's motion blur looks slightly off for how fast it appears to be falling; the plate looks essentially motionless, apart from perhaps a barely-noticeable settling wobble in the very first instant of the clip; a bright glint briefly shows on the wrong side of a droplet for an instant; none of these small issues are enough to confuse what's happening in the demonstration.
level_4: Everything in level 3 holds, plus: motion blur always matches how fast things are actually moving; the plate looks completely motionless for the rest of the clip, with no further wobble at all; shadows and highlights fall on the side you'd expect from a fixed light source and a static camera; every edge (the plate's rim, each droplet's outline) stays sharp and doesn't flicker.
level_5: Everything in level 4 holds, plus: falling droplets trace a smooth, steadily speeding-up path with no stutters, backward jumps, or unnatural changes in speed; the plate's brightness and color look steady and unchanging for the entire clip; there's no visible glitching, ghosting, doubled edges, or warped-looking artifacts anywhere; the whole clip reads as one continuous, consistently lit take.