Domain: Natural Science — Physics
Target concept: Recoil motion

Video generation prompt: Pinch the mouth of the balloon to ensure it is airtight, hold a fully inflated balloon in your hand, and then release the air inside the balloon by letting go.

Evaluation guide:
(i) Target concept: Conservation of momentum in a closed system undergoing internal mass ejection.
Minimum mechanism: Balloon must contain compressible gas under pressure; mouth must be sealed then opened to enable directed exhaust; balloon structure must be deformable yet retain axial symmetry during ejection to produce linear recoil.
(ii)Storyline: [Frame 0–2] Hand approaches and precisely pinches balloon mouth → [Frame 3–5] Balloon held taut and motionless, visibly inflated → [Frame 6] Fingers begin separating at mouth → [Frame 7] Air jet emerges coaxially from mouth → [Frame 8] Balloon simultaneously recoils linearly opposite to jet direction → [Frame 9] Recoil continues with sustained jet and symmetric collapse; all events occur from fixed frontal viewpoint with balloon centered, mouth always visible, no occlusion, no perspective shift.

Manual:
Experimental Procedure
1. Pinch the mouth of a fully inflated balloon with fingers to seal it.
2. Hold the inflated balloon stationary in hand.
3. Release the pinch to let air escape.
Observation of Experimental Phenomena
The balloon recoils backward (away from the hand) as a directed jet of air exits its mouth.
Summary of Experimental Principles
Recoil motion demonstrates Newton"s Third Law: the force of air ejecting forward produces an equal and opposite reaction force pushing the balloon backward.

Prompt Grounding rubric:
level_1: No balloon appears in the frame, or no hand appears, or none of the three setup actions (pinching the balloon's mouth shut, holding it while inflated, and releasing the pinch) occurs in any recognizable form; a balloon that starts deflated is never inflated, pinched, or released.
level_2: A balloon and a hand are both visible, but at least two of the three setup actions cannot be identified: for example the hand never visibly pinches the balloon's mouth (it grips the body instead), the balloon is never shown fully inflated before release, or the fingers open with no pinch shown beforehand.
level_3: All three setup actions occur in the correct order (the hand pinches the balloon's mouth, the balloon is held while visibly inflated, and the fingers then release the pinch), but one of them is hard to read: the pinch location is ambiguous, the balloon's inflated shape is indistinct, or the release looks like the hand pulling away rather than the fingers opening.
level_4: All three setup actions are clearly visible and correctly ordered (fingers close specifically around the balloon's mouth, the balloon is held taut and rounded while inflated, and the fingers open to release it), with no step skipped, reordered, or replaced by an unrelated motion.
level_5: All three setup actions are as clear and correctly ordered as in score 4, and additionally: the pinch is localized only at the mouth opening with no incidental grip on the balloon's body, the inflated hold phase shows a consistently taut, rounded balloon with no sagging, and the release reads as one deliberate finger-opening motion rather than a vague withdrawal of the hand.

Scientific and Causal Correctness rubric:
level_1: No motion of the balloon occurs after release, or the balloon moves toward the hand instead of away from it, or the balloon appears to inflate further at the moment of release, or no jet of air is visible exiting the mouth and no backward motion of the balloon occurs.
level_2: The balloon moves after release, but not backward away from where it was held: for example it moves sideways or spins in place without traveling backward; or it begins moving before the fingers release the mouth; or no air jet is visible and the balloon's motion appears unconnected to the release; or the mouth opening widens outward instead of narrowing as air escapes.
level_3: After release, the balloon moves backward, away from where it was held, while a visible jet of air exits its mouth; but the jet is not aligned with the balloon's long axis, the direction of balloon motion does not clearly correspond to the jet's direction, the jet appears to pulse on and off rather than flow steadily, or the balloon body collapses unevenly to one side as air escapes.
level_4: The jet exits straight along the balloon's central axis and the balloon recoils in the directly opposite direction; the jet and the recoil begin together at release; the balloon collapses roughly symmetrically as it recoils; no forward motion or spinning occurs; but one small inconsistency remains, e.g., the jet's visible strength tapers off unevenly, or the balloon rocks slightly off-axis partway through the recoil.
level_5: The jet exits continuously and steadily along the balloon's central axis from the instant of release, and the balloon recoils smoothly in the exact opposite direction without spinning, rocking, or sagging to one side; the jet and the recoil evolve together throughout, with the balloon's backward motion visibly driven by, and matched in timing to, the escaping air.

Spatiotemporal Consistency rubric:
level_1: The balloon or the hand vanishes from view and reappears in a later frame; the balloon's size changes abruptly from fully inflated to flat within a single frame with no visible deflation motion; the hand's position relative to the balloon jumps discontinuously, e.g., from touching the mouth to far away with no travel shown; or the lighting abruptly shifts from bright to dark (or back) between shots with no light source change to explain it.
level_2: The balloon or hand becomes visibly warped or distorted (e.g., the balloon's rounded shape stretches or shears unnaturally); the balloon's surface texture flickers on and off between frames; or the recoil motion freezes momentarily and then jumps ahead rather than flowing continuously.
level_3: The balloon and hand keep a consistent shape and visible spatial relationship throughout (the hand stays near the balloon's mouth through the pinch, hold, and release, the balloon stays fully within the frame, and its recoil after release reads as continuous rather than jumpy), but one small flaw is present, e.g., the balloon's outline blurs unevenly during recoil, or the fingers appear to shift slightly out of contact for an instant during the hold with no visible cause.
level_4: All the continuity described in score 3 holds with no such flaw (the balloon's shape, the hand's position, and the recoil path all track smoothly and continuously from pinch through release with no visible drift, stutter, or blur inconsistency), but one very minor deviation remains, e.g., the balloon's centerline appears to wobble very slightly as it recoils without otherwise breaking the sense of continuous motion.
level_5: The balloon and hand show no visible drift, warping, flicker, or discontinuity at any point: the balloon's shape and position relative to the hand track smoothly and continuously from the pinch through the hold and into the recoil, with the recoil path appearing as one continuous, physically coherent trajectory rather than a series of disconnected jumps.