Domain: Natural Science — Physics
Target concept: Refraction of light (the bent chopstick)

Video generation prompt: Half-fill a glass cup with clear water, insert a bamboo chopstick diagonally into the water, and observe from the side.

Evaluation guide:
(i) Target concept: Refraction-induced angular displacement of a linear object at a planar air–liquid interface.
Minimum mechanism: Light rays from the submerged chopstick segment change direction at the water surface due to differing optical densities; observer"s eye receives these refracted rays, reconstructing a virtual image of the submerged segment at a laterally shifted position relative to the real air segment.
(ii)Storyline: [1] Stable setup: upright glass cup with horizontal water surface → [2] Diagonal chopstick insertion: rigid entry causing no splash or surface disturbance → [3] Static equilibrium: chopstick fully settled, no motion, water surface calm and planar → [4] Side-view observation: fixed viewpoint aligned with cup mid-height, capturing full lateral cross-section including air–water interface → [5] Visual perception: continuous chopstick in air, abrupt angular shift at interface, straight submerged segment laterally offset — no intermediate curvature, no double imaging, no color separation.

Manual:
Experimental Procedure
1. Place a transparent glass cup on a stable surface.
2. Pour clear water into the cup until it is approximately half-full.
3. Hold a natural bamboo chopstick and insert it diagonally into the water so that part remains above and part is submerged.
4. Position camera at eye level, perpendicular to one side of the cup, capturing full lateral view.
Observation of Experimental Phenomena
The chopstick appears bent or broken at the water surface — the submerged portion is laterally displaced relative to the part above water, creating a visible angular discontinuity at the air–water interface.
Summary of Experimental Principles
Light refracts when passing from air (less dense medium) into water (more dense medium), changing direction toward the normal. This causes the submerged portion of the chopstick to appear shifted, producing the illusion of bending.

Prompt Grounding rubric:
level_1: No transparent glass cup is shown, no water is visible in it, no chopstick appears in the frame, there is no diagonal insertion of a chopstick into water, and the camera is not framed from the side of the cup.
level_2: A glass cup is visible but it is either empty or filled to the brim rather than half full; a chopstick may be present but it is not inserted into the water (e.g., it lies flat on the table, stands upright above the water line, or dips in only vertically); the camera view is not a side/eye-level shot (e.g., top-down or angled from above).
level_3: The cup is upright and roughly half filled with clear water; a bamboo chopstick is inserted into the water at a diagonal angle; the camera shows a side view of the cup; however the chopstick's submerged tip is not visible, the water surface is tilted or uneven, or the chopstick does not actually touch the water.
level_4: The cup is upright, stable, and half filled with clear water; the chopstick enters the water diagonally with one segment above the surface and one below it; the water surface is level and horizontal; the chopstick makes visible contact with the water; the side-view camera captures the full cup, water surface, and both chopstick segments without anything blocking the interface.
level_5: Everything required at the 4-point level is present, and in addition the chopstick's entry angle is clearly oblique rather than near-vertical (a viewer can tell at a glance it is slanted against the cup wall); the cup stays upright and does not tip, drift, or rotate; the chopstick is rendered as one continuous rod from tip to top with no broken or missing segment at the waterline; and the side-on framing centered on the air-water boundary is held steady for the whole clip.

Scientific and Causal Correctness rubric:
level_1: The chopstick looks perfectly straight along its whole length; there is no visible break, bend, or offset where it crosses the water surface, i.e., no refraction effect is depicted at all.
level_2: The chopstick appears to bend or break, but at the wrong place (e.g., at the rim of the cup, in mid-air, or below the true waterline) rather than exactly at the water surface, or the bend goes the wrong way (the submerged part looks displaced away from the surface normal instead of toward it), or the water is so opaque or tinted that the submerged segment cannot be seen at all.
level_3: A bend appears right at the water surface, but the submerged segment is not smoothly continuous with the above-water segment (e.g., it looks offset sideways with a visible gap, or the chopstick appears kinked/zig-zagged rather than showing one clean angular break consistent with the diagonal insertion).
level_4: The chopstick bends exactly at the horizontal water line; the submerged portion is shifted laterally toward the viewer relative to where a straight extension of the above-water portion would fall, matching the direction expected for light bending toward the normal on entering water; the submerged segment itself stays straight; there is no double image, ghosting, or mirrored duplicate of the chopstick at the interface.
level_5: Everything required at the 4-point level is present, and in addition the single angular break at the surface reads as one clean, smooth transition with no extra curvature or waviness along the submerged segment; the submerged wood keeps the same color and grain pattern as the part above water (no unnatural color fringe, glow, or transparency change at the boundary); and the apparent lateral offset is proportional to the chopstick's insertion angle, so a viewer would judge the bend as physically believable rather than arbitrary.

Spatiotemporal Consistency rubric:
level_1: Severe continuity breaks: the cup's position or orientation changes abruptly between frames with no motion shown; the chopstick disappears and reappears, or instantly relocates within the water; the water surface churns violently and then freezes mid-motion; the cast shadow beneath the cup jumps to the opposite side of the light source with no camera movement to explain it.
level_2: Noticeable but less extreme problems: the chopstick rotates or slides slightly with no hand or physical cause; the cup wobbles or tips more than a stable setup would allow; ripples on the water surface grow and shrink at an irregular, non-physical rate; the chopstick shows a visible gap or overlap right where it crosses the waterline, as if the two halves belong to different objects.
level_3: Small but noticeable slips: the cup drifts slightly across the shot even though nothing touched it; the water surface shimmers unevenly frame to frame even though the chopstick is at rest; a bright highlight on the water or chopstick jumps to a new spot without the camera or chopstick moving.
level_4: The cup stays in one fixed spot and orientation for the whole clip; once inserted, the chopstick holds its position and angle without drifting; the water surface stays flat and calm; the highlights and shadows keep the same direction and strength throughout, matching a single unmoving light source; the chopstick and the cup rim never show a gap or overlap where they meet.
level_5: Everything required at the 4-point level is present, and in addition there is no visible flicker or strobing in the water's surface reflections, no sudden softening or sharpening of focus on the chopstick or waterline, and the submerged and above-water segments of the chopstick line up as one continuous rod in the same place in every frame of the clip, with no shimmering or shape change at the boundary.