Domain: Natural Science — Physics
Target concept: Comparison of a ball projected horizontally from a desk and a vertically falling object

Video generation prompt: Two identical balls are at the same table height: one is horizontally launched from the edge of the table, while the other is simultaneously dropped vertically. The scene shows both balls until they reach the ground.

Evaluation guide:
(i) Target concept: Independence of horizontal and vertical motion components under uniform gravitational acceleration.
Minimum mechanism: Both balls must experience identical vertical acceleration from rest, with zero initial vertical velocity for both, and no net vertical force difference; horizontal launch imparts no vertical impulse; same release height and simultaneity are required for observable synchronous impact.
(ii)Storyline: [Frame 0] Two identical balls stationary, aligned at table edge, same height. [Frame 1–2] Both released simultaneously: one pushed horizontally (visible forward impulse), one dropped (no lateral motion). [Frames 3–N−2] Both balls descend with identical vertical position progression; horizontal ball moves forward continuously; vertical ball stays aligned under release point. [Frame N−1] Both balls approach ground at equal vertical speed and same height above ground. [Frame N] Both make ground contact in same frame; no staggered impact. Perspective: fixed frontal/side view showing full table-to-ground vertical extent and unobstructed lateral field for horizontal motion; no camera motion or zoom; lighting enables clear shadow and contour visibility.

Manual:
Experimental Procedure
1. Place two identical balls side-by-side at the edge of a level table, aligned at same height.
2. Simultaneously release one ball horizontally off the edge and the other vertically downward from rest — both starting from identical height.
3. Record until both balls contact the ground.
Observation of Experimental Phenomena
Both balls strike the ground at the same instant; their vertical positions match frame-for-frame during descent; the horizontally launched ball travels forward while falling, but neither leads nor lags in vertical motion.
Summary of Experimental Principles
In the absence of air resistance, horizontal and vertical motions are independent; vertical acceleration due to gravity is identical for both objects, so they fall the same vertical distance in the same time — confirming independence of motion components.

Prompt Grounding rubric:
level_1: No two balls are present, or only one ball appears; or the two balls are not visually identical (different color, size, or texture); or no table or desk edge is visible; or no ground surface is visible; or neither a horizontal launch nor a vertical drop action is depicted.
level_2: Two similar-looking balls and a table and ground are visible, but the setup is incomplete: e.g., the two balls do not start from the same height on the table edge; the horizontally launched ball simply appears mid-air instead of being released from the table edge; the vertically dropped ball starts falling without a visible moment of release from rest; or one ball clearly begins moving well before the other.
level_3: Two identical balls appear at the same table-edge height; one is clearly launched horizontally off the table while the other is clearly released straight down from the same height; both releases happen within the same visible moment with no delay between them; the table and the ground are both fully visible; no extraneous object blocks either ball during its fall.
level_4: All conditions for the score 3 are met, AND both balls stay within one continuous camera framing that keeps the table edge and the ground in view together, AND the two balls keep the same visual identity as each other throughout (same size, color, and texture, and never swapped for a different-looking ball), AND no new object enters the scene after the initial release that could be mistaken for a third ball.
level_5: All conditions for the score 4 are met, AND the horizontally launched ball and the vertically dropped ball are each identifiable as their assigned role from the very first frame purely by their release point and initial direction of travel, AND the frame keeps the full table-to-ground vertical span in view for the entire sequence, AND nothing about the original two-ball, one-table, one-ground setup is altered, added to, or removed at any point.

Scientific and Causal Correctness rubric:
level_1: Phenomenon contradicts physics: e.g., the vertically dropped ball reaches the ground before the horizontally launched ball, or the horizontally launched ball visibly rises or hovers instead of falling; or the two balls fall at visibly different vertical rates; or the vertically dropped ball drifts sideways; or the horizontally launched ball stops descending mid-flight.
level_2: The vertical descent of the two balls is not matched: e.g., one ball visibly speeds up faster than the other in the vertical direction, or one ball falls at a constant speed while the other accelerates; or the two balls hit the ground with a clearly separate, distinguishable landing moment for each rather than together; or the horizontally launched ball shows no forward travel while it falls.
level_3: The horizontally launched ball and the vertically dropped ball descend at a visually matched vertical rate: their heights above the ground stay aligned frame by frame through the whole fall; the horizontally launched ball keeps moving forward the whole time; the vertically dropped ball shows no sideways drift; both reach the ground surface with no floating, hovering, or sinking into it.
level_4: All conditions for the score 3 are met, AND the two balls' centers stay level with each other throughout the fall (their shared starting height is never lost to drift), AND the horizontally launched ball traces a visibly curved (parabolic) downward path rather than a straight or rising one, AND the vertically dropped ball falls in a straight line with no sideways curve or wobble.
level_5: All conditions for the score 4 are met, AND at every point in the fall the two balls have dropped the same vertical distance from their release height, so their heights above ground are visually indistinguishable at any given moment, AND the horizontally launched ball's forward travel keeps increasing while its vertical drop matches the other ball's exactly, AND the two balls are never seen more than about one ball-width apart in height while both are still airborne.

Spatiotemporal Consistency rubric:
level_1: A severe spatiotemporal break occurs: e.g., a ball disappears from one spot and reappears elsewhere; a ball's size or orientation suddenly changes for no motion-related reason; the lighting shifts abruptly partway through the fall; the table or ground geometry warps; a ball splits into pieces; or a ball's shadow vanishes and comes back inconsistently.
level_2: A moderate break occurs: e.g., one ball is briefly blocked from view by an object that was not part of the original setup; a ball's shadow changes direction or disappears for a few frames while the other ball's does not; there is a visible jump-cut between frames; motion blur briefly makes it unclear which ball is which; or the table surface flickers or changes texture partway through.
level_3: Both balls stay continuously visible and spatially stable aside from their falling motion; the table and the ground keep a consistent look and shape throughout; shadows for both balls stay present and point in the same direction the whole time; the fall plays out as one continuous motion with no cuts, freeze-frames, or stutter.
level_4: All conditions for the score 3 are met, AND the camera framing never pans, tilts, or zooms, AND the two balls' spatial relationship to each other changes only as expected from their different fall paths (no unexplained drifting apart or together), AND the apparent distance between the two balls in the frame changes smoothly, with no sudden perspective jump that makes them look closer or farther apart than the fixed side view would show.
level_5: All conditions for the score 4 are met, AND both balls' motion is smooth from start to finish with no stutter, judder, or unexplained speed change, AND each ball's shadow shifts continuously and in step with its position, AND no frame shows a rendering glitch (such as a warped edge, a flickering outline, or a see-through patch) on either ball, the table, or the ground.