Domain: Natural Science — Physics
Target concept: A ball in a curved bowl, when displaced, returns to the bottom of the bowl.

Video generation prompt: A small ball is at rest at the bottom of a curved bowl; a hand pushes it up along the inner wall of the bowl and then releases it.

Evaluation guide:
(i) Target concept: Stable mechanical equilibrium in a gravitational potential well
Minimum mechanism: Bowl must be concave and rigid; ball must be solid and subject only to gravity and contact forces; no external forces (e.g., wind, magnetism, or propulsion) act after release; surface must provide sufficient friction to prevent slipping during roll
(ii)Storyline: [Frame 0–2] Ball motionless at lowest point of bowl; [Frame 3–5] Hand enters, contacts ball, and pushes it upward while maintaining contact with inner wall; [Frame 6] Hand fully separates from ball (release event); [Frame 7–9] Ball begins descending along same inner wall path; [Frame 10] Ball reaches bottom and stops, all under fixed viewpoint, no occlusion, no camera motion

Manual:
Experimental Procedure
1. Place a small solid ball at rest at the exact lowest point inside a stationary, smooth, concave curved bowl.
2. A hand enters the frame, makes contact with the ball, and pushes it upward along the inner wall of the bowl.
3. The hand fully releases contact with the ball and withdraws from the frame.
Observation of Experimental Phenomena
After release, the ball moves downward along the inner wall, returns to the bottom of the bowl, and comes to rest at its original position.
Summary of Experimental Principles
When the ball sits away from the bottom of the bowl, gravity has a component acting tangent to the bowl's curved surface — pointing back down along the slope toward the lowest point. This tangential component is what pulls the ball back, and it shrinks to zero exactly at the bottom, which is why the bottom is a stable equilibrium. The normal force from the bowl's surface acts perpendicular to that slope; together with the perpendicular component of gravity it keeps the ball moving along the curved surface (supplying the centripetal acceleration needed to follow that curve), but it is the tangential gravity component — not this radial balance — that actually restores the ball to the bottom.

Prompt Grounding rubric:
level_1: No bowl, ball, or hand is visible; there is no push-then-release sequence; the scene is unrelated to a ball-in-bowl setup (e.g., a ball on a flat table, an open-air scene, or a container that isn't bowl-shaped).
level_2: A bowl and a ball are both visible but the setup is wrong (e.g., the ball starts outside the bowl, the bowl is upside-down, or the bowl's inner surface is not curved); a hand appears but never touches the ball, or the hand pushes the ball without ever fully releasing it.
level_3: A curved bowl is shown with the ball resting at its lowest point at the start; a hand enters, contacts the ball, pushes it up along the bowl's inner wall, and then fully withdraws from frame before the ball begins moving back; the moment of release is clearly visible as the hand separating from the ball.
level_4: Everything required for score 3 is present, and in addition: the bowl's inner surface is visibly smooth and concave with no flat, angular, or convex sections; the ball stays in contact with that inner wall throughout the push; the hand is fully out of frame and stays out for the entire return motion.
level_5: Everything required for score 4 is present, and in addition: the hand's push is clearly directed along the bowl's curved surface rather than lifting the ball straight up or slipping off it; the ball's starting position is centered at the bowl's lowest point; no unrelated object, occlusion, or camera cut interrupts the sequence from start to finish.

Scientific and Causal Correctness rubric:
level_1: After being released, the ball does not return toward the bottom: it stays where it was pushed, keeps moving away, rolls out of the bowl entirely, or accelerates upward instead of falling back, none of which is consistent with a restoring force pulling it toward equilibrium.
level_2: The ball moves back toward the bottom of the bowl but stops short of its original resting spot, or overshoots and bounces noticeably upon arrival, or its return motion is interrupted by a pause, jump, or teleport instead of being continuous from the moment of release.
level_3: Once released, the ball travels down along the bowl's inner wall and comes to rest at or very near its original starting point at the bottom; it does not fly out of the bowl, slide sideways out of the curve, or bounce away; its direction of travel reverses exactly once, from ascending to descending.
level_4: Everything required for score 3 is present, and in addition: the ball's downward path visibly follows the curvature of the bowl's inner wall rather than dropping straight down or separating from the surface; once it settles at the bottom it stays still with no rocking or drifting; nothing besides gravity and the bowl's surface appears to act on it after release.
level_5: Everything required for score 4 is present, and in addition: the ball's whole motion reads as one smooth reversal (rising, slowing to a momentary stop at its highest point, then falling back down and gradually settling at the bottom), with no visible overshoot past the bottom, no repeated back-and-forth oscillation, and no asymmetry between how it rose and how it fell.

Spatiotemporal Consistency rubric:
level_1: The bowl or the ball vanishes or reappears at some point in the video; the hand teleports from one position to another between frames; the ball changes size or shape mid-motion; the lighting on the scene shifts abruptly, as if the ball's shadow suddenly vanishes and then reappears with no cause; the bowl itself rotates or deforms without the hand touching it.
level_2: The bowl or ball flickers out of view for a moment before reappearing; the hand overlaps or occludes the ball inconsistently from one frame to the next; the ball's motion visibly jumps or freezes for a beat during the push or the return; the background shifts or the camera appears to zoom.
level_3: The bowl, ball, and hand each keep a consistent size, shape, and presence throughout; the hand's push motion is continuous with no gaps; the ball moves without stutter, jump, or freeze; the bowl stays fixed in the frame with a stable orientation.
level_4: Everything required for score 3 is present, and in addition: the ball stays in contact with the bowl's inner surface during both the push and the return, never appearing to float above it or sink through it; the hand never passes through the bowl's rim or wall; the ball never appears to be simultaneously behind and in front of the bowl's edge in a way that breaks depth ordering.
level_5: Everything required for score 4 is present, and in addition: the ball's speed visibly increases as it descends and eases off as it nears the bottom, with no sudden unnatural speed-up or freeze; the ball and bowl never appear to pass through one another; no part of the scene stretches, warps, or shifts perspective at any point in the video.