Domain: Natural Science — Physics
Target concept: The size of a shadow is related to the distance between the object and the light source; for an elevated point light source and an object standing on the same ground plane, the closer the object is to the light source, the shorter (smaller) the shadow.

Video generation prompt: In a dimly lit square, a wooden pole stands upright, with only a streetlight in the distance serving as the light source. Gradually moving the wooden pole toward the light source, observe the changes in the length and position of the shadow cast by the pole under the light.

Evaluation guide:
(i) Target concept: Direct geometric relationship between object-light horizontal distance and shadow length when the object and an elevated point light source stand on the same ground plane: as the pole's horizontal distance to the streetlight decreases, its shadow becomes shorter, shrinking toward the pole's base as the pole nears the light; as the distance increases, the shadow becomes longer.
Minimum mechanism: A single dominant elevated point light source (streetlight) illuminating an opaque upright object (wooden pole) standing on the same planar ground surface, with a fixed viewpoint enabling unambiguous spatial tracking of pole position and shadow tip.
(ii)Storyline: Frame 1: Pole far from streetlight → long shadow, its tip far from the pole's base. → Causal transition: Pole displacement reduces the horizontal object-light distance → the line from the elevated light to the pole's top meets the ground closer to the pole. → Frame middle: Pole midway → shadow visibly shorter, tip closer to the pole. → Causal transition: Continued reduction in object-light distance further shortens the projected shadow. → Final frame: Pole near streetlight → shadow shortest, shrinking close to the pole's base. Perspective constraint: Fixed frontal/slightly elevated view showing full pole, full shadow, and streetlight in the same frame; visibility constraint: No occlusion between pole, light, or shadow-casting ground region.

Manual:
Experimental Procedure
1. Place a wooden pole upright on the ground in a dimly lit open square.
2. Position a single streetlight at a visible distance, serving as the sole light source.
3. Move the pole steadily toward the streetlight over ~10 seconds.
Observation of Experimental Phenomena
As the pole moves closer to the streetlight, its shadow on the ground becomes progressively shorter and its tip moves closer to the pole's base.
Summary of Experimental Principles
For an object and an elevated point light source that share the same ground plane, shadow length is directly related to the horizontal distance between them: the closer the object is to the light source, the shorter its shadow; the farther away, the longer the shadow.

Prompt Grounding rubric:
level_1: No wooden pole is shown standing upright; no streetlight appears anywhere in the shot; the setting is not a dim square at night; the pole does not move toward any light source.
level_2: A wooden pole and a streetlight both appear in a square-like setting, but the pole never moves toward the streetlight, or the streetlight is not clearly farther away than the pole at the start, or the scene is brightly lit rather than dim (e.g., daylight or multiple lit sources).
level_3: An upright wooden pole stands in a dimly lit square with exactly one streetlight visible in the distance; the pole moves continuously from a position far from the streetlight to a position near it, all within a single continuous shot from one fixed camera position.
level_4: All conditions of the 3-point level are met, and the pole stays upright the whole time (it never tilts or falls over), the streetlight is the only light source in the frame (no other lamps, headlights, or glow sources), and the background brightness stays constant with no added illumination or flicker.
level_5: All conditions of the 4-point level are met, and the base of the pole stays planted in the same spot on the ground while it moves (it does not slide sideways, lift off the ground, or float), the streetlight itself never moves or becomes blocked from view, and the square's ground and horizon look spatially consistent and undistorted from the first frame to the last.

Scientific and Causal Correctness rubric:
level_1: No shadow is visible at any point in the video; or a shadow is visible but its length never appears to change as the pole moves; or the shadow visibly grows longer as the pole approaches the streetlight, which is the physically backwards outcome for this ground-plane geometry.
level_2: A shadow is present but changes inconsistently with the pole's motion: e.g., it lengthens during part of the approach and shortens during another part with no clear overall trend, or the shadow's position jumps to a new location the pole has not yet reached, or the shadow appears detached from the pole's base.
level_3: A shadow is cast from the pole onto the ground, and as the pole moves closer to the streetlight, the shadow visibly shortens and its tip moves closer to the pole's base, consistent with a single elevated point light source and the pole and light sharing the same ground plane.
level_4: All conditions of the 3-point level are met, and the shadow's edge stays attached to and originates from the pole's base in every frame (no gap or misalignment); the shadow remains a single continuous shape throughout the motion with no secondary or duplicate shadow appearing.
level_5: All conditions of the 4-point level are met, and the shortening of the shadow is steady and progressive with no point at which it visibly lengthens or holds still while the pole keeps approaching; the shadow tip moves smoothly toward the pole's base as the pole nears the light, and the shadow's outline stays aligned with the pole's vertical axis without visibly bending or warping.

Spatiotemporal Consistency rubric:
level_1: The pole abruptly appears at a new position without visibly moving there; the streetlight flickers, vanishes, or reappears at any point; the shadow disappears mid-motion and then reappears in a different place; the shot cuts away and resets to an earlier moment.
level_2: The pole's approach toward the streetlight shows one clearly visible jump (a moment where it is suddenly closer or farther than its prior motion would predict) with no smooth movement filling the gap; or the shadow blinks in or out of existence independent of the pole's motion; or the overall brightness of the square suddenly changes partway through with no visible reason.
level_3: The pole travels smoothly and continuously toward the streetlight in a single direction with no visible skips; the shadow's length and position change continuously as the pole moves, without interruption; the square's overall brightness stays even throughout; the pole and streetlight keep their solid shape with no visible warping, clipping, or breaking apart.
level_4: All conditions of the 3-point level are met, and the camera position, angle, and zoom never change during the shot; the pole's height and thickness look the same in every frame; the ground's texture and the perspective of the square stay consistent from the near end to the far end of the shot.
level_5: All conditions of the 4-point level are met, and the motion of the pole and its shadow looks fluid throughout with no visible freezing, stutter, or repeated frame; the shadow's edge stays sharp and steady rather than flickering or pulsing; the relative positions of the pole, its shadow, and the ground stay visually coherent with no floating or misaligned elements as the pole moves.