Domain: Natural Science — Physics
Target concept: Floating ball

Video generation prompt: A blower is placed on a horizontal table, with the airflow direction perpendicular to the horizontal table, maintaining a stable air force; a ping-pong ball is placed at the outlet of the blower and then released from rest.

Evaluation guide:
(i) Target concept: Stable levitation of a lightweight spherical object at the center of a vertical laminar air jet due to pressure differential equilibrium.
Minimum mechanism: Air must exit the blower as a coherent, axisymmetric, vertically oriented jet; ball must be low-mass, spherical, and non-aerodynamic (smooth surface); table must be rigid and horizontal to prevent destabilizing tilt; no external forces (wind, vibration, drafts) may perturb the system.
(ii)Storyline: [Frame 0–1] Blower fully visible, base flush with flat table surface, outlet facing straight up; [Frame 2–3] Hand places ball centered over outlet; [Frame 4] Hand fully withdraws; [Frame 5] Ball released from rest: no downward/upward impulse; [Frame 6–end] Ball lifts <1 cm and stabilizes in fixed position: centered, non-rotating, non-translating, non-contacting, with airflow visibly emanating symmetrically from outlet rim; viewpoint is fixed frontal/slightly elevated, fully capturing blower base, outlet, ball, and immediate surroundings without occlusion.

Manual:
Experimental Procedure
1. Place a cylindrical blower upright on a flat horizontal table.
2. Orient blower so airflow exits vertically upward, perpendicular to table surface.
3. Gently place a standard white ping-pong ball centered over the blower outlet.
4. Release the ball from rest — no push or throw.
Observation of Experimental Phenomena
The ball lifts slightly and remains stably suspended, motionless and centered directly above the blower outlet without contacting it.
Summary of Experimental Principles
Vertical support of the ball comes mainly from momentum transfer: the blower's air jet continuously strikes the underside of the ball, and the resulting dynamic pressure (drag force) of the moving air balances the ball's weight. If the ball drifts slightly off the jet's centerline, the fast-moving air in the jet core has lower pressure than the slower surrounding air (a Bernoulli-type pressure difference), and this pressure imbalance pushes the ball sideways back toward the jet axis. The combination of vertical drag support and lateral pressure-differential restoring force is what keeps the ball hovering in a stable, centered position above the outlet — not Bernoulli's principle acting alone.

Prompt Grounding rubric:
level_1: The blower or the ping-pong ball is missing from the scene, or the blower does not rest on a horizontal table, or the blower's outlet does not visibly point straight up (perpendicular to the tabletop), or the ball is never shown positioned at the outlet before release, or the ball is never seen centered over the outlet at any point in the clip.
level_2: The blower and the ball are both present and the blower sits on a horizontal table with the ball shown at the outlet at the start, but the outlet does not point vertically upward (it looks tilted or angled to one side), or the ball is released and immediately flies off or drops to one side with no interval of centered hovering at all.
level_3: The blower sits on a visibly horizontal table with its outlet pointing straight up; the ball is placed by hand at the outlet and released from rest (no push or throw); the ball hovers near the outlet's center for at least one continuous stretch of the clip, but the hovering looks unsteady: it wobbles noticeably, drifts off to the side and back repeatedly, or occasionally brushes the outlet's rim.
level_4: The setup matches the 3-point description, and once released the ball stays centered over the outlet for the whole visible hovering phase without touching the housing or drifting past the outlet's rim, with any side-to-side motion staying within roughly one ball-width; the only shortcoming is a secondary framing issue, such as the table's flatness or the blower base's contact with the table not being clearly shown, or the hand briefly blocking the outlet during placement.
level_5: The blower's base sits flush and visibly still on the horizontal table with the outlet facing straight up and fully visible; the ball is placed by hand directly onto the outlet's center with the placement fully visible (no hand occlusion), released from rest, and stays centered over the outlet for the entire hovering phase with no contact with the housing, no drift past the outlet's rim, and no visible wobble or tilt; the fixed camera keeps the blower base, outlet, and ball simultaneously in frame throughout, with no cropping or cuts.

Scientific and Causal Correctness rubric:
level_1: The video shows no causal connection between the airflow and the ball's behavior: the ball hovers with no airflow cues at all near the outlet (no streamer, dust, or fabric motion), or it falls straight to the table while airflow cues are clearly present, or it shoots straight up off the jet and flies out of frame.
level_2: Airflow cues near the outlet (a streamer, tissue strip, or dust caught in the moving air) and the ball are both visible, but the ball either drops back onto the table right after release, launches upward and leaves the frame, or never leaves the tabletop at all; no sustained hovering above the outlet is shown.
level_3: The ball lifts off the table and hovers somewhere above the outlet while airflow cues confirm the jet is running, but the hovering position drifts noticeably away from the jet's centerline for extended stretches, or the ball only starts hovering after being nudged or tapped by hand rather than settling there after simply being released.
level_4: The ball settles into hovering directly above the outlet on its own after a passive release (no nudge or tap needed), and airflow cues show the jet running continuously for the entire hovering period; the visible portion of the jet spreads out roughly evenly on both sides the camera can see, but a full view of the jet's symmetry all the way around the outlet is not shown (for instance, only cues facing the camera are visible, with none on the far side).
level_5: Airflow cues are visible on multiple sides of the outlet and show the jet spreading outward evenly in every visible direction, confirming a symmetric jet rather than a lopsided one; the ball hovers steadily above the outlet within moments of release, needing no repeated hand adjustment; and whenever the ball drifts slightly off the jet's centerline from natural air turbulence, it visibly settles back toward the centerline rather than drifting further away or falling, showing the self-correcting, pressure-driven nature of the levitation rather than the ball simply sitting still in one spot.

Spatiotemporal Consistency rubric:
level_1: A severe break in continuity occurs: the ball or the blower vanishes and reappears at a different spot with no motion connecting the two, the table surface visibly buckles or cracks, the lighting flips abruptly (a sudden switch to much brighter or darker), or the footage cuts jarringly in the middle of the ball's motion.
level_2: Multiple noticeable but non-catastrophic breaks occur: the ball flickers in and out of view, the blower's position jumps between frames with no visible motion connecting the two, the round outlet momentarily distorts into an oval shape and back, or the ball's shadow on the table moves in a direction unrelated to the ball's own motion.
level_3: A single minor flaw is visible: for example the ball briefly shows a doubled or smeared outline during a fast moment with no clear direction of motion, or a highlight on the ball's surface disappears for one frame and reappears the next, or the ball's shadow lags slightly behind the ball's position for an instant; but the overall arrangement (blower on the table, ball above the outlet) stays clearly readable throughout.
level_4: The blower shows no perceptible shift in its base position across the whole clip, the table and outlet keep a constant size and shape, and there is no teleporting, flickering, or abrupt lighting/shadow change anywhere; the only imperfection is a small timing gap between the hand leaving the frame and the ball's release, such as the hand withdrawing a moment before the ball is shown being let go rather than the two happening together.
level_5: The blower's base shows no visible shift, tilt, or deformation for the entire clip; the ball never flickers, jumps, or leaves a duplicate or ghost image; shadows on the table shift in a way that matches one fixed, unmoving light source and a static camera; and the hand's release of the ball is shown as one continuous, uninterrupted motion with no visible gap between letting go and the ball beginning to move, with every object keeping the same relative scale and position throughout.