Domain: Natural Science — Physics
Target concept: Water waves passing through a water–oil interface

Video generation prompt: In a wavy channel, a thin, taut, flexible, watertight membrane spans the full depth and width of the channel, forming a straight vertical boundary that keeps water on one side and oil on the other side without letting them mix; a point source in the water generates circular water waves that propagate toward this membrane boundary.

Evaluation guide:
(i) Target concept: Partial reflection and transmission of mechanical surface waves at a water–oil boundary formed by a thin, flexible, wave-transmitting membrane, arising from the mismatch in fluid loading (impedance) between water and oil on either side of the membrane.
Minimum mechanism: A thin, taut, flexible, watertight membrane spans the full depth and width of the channel, keeping water and oil apart while still transmitting wave-induced displacement across the boundary; wave generation must be localized and isotropic in the water; because water and oil differ in density, they load the membrane unevenly, producing continuity of displacement but a mismatch in the restoring force at the boundary, manifesting as a preserved wavefront center, amplitude reduction, and a change in propagation speed as waves cross from water into oil.
(ii)Storyline: [Phase 1] Static setup: water and oil occupy adjacent halves of the channel, separated by the taut membrane forming a sharp, straight, motionless boundary; point source inactive and visible in the water. [Phase 2] Initiation: point source activates → circular wavefronts emerge symmetrically in the water only. [Phase 3] Propagation: wavefronts expand uniformly, maintaining circular shape and center, approaching the membrane boundary without distortion. [Phase 4] Interaction: wavefronts contact the membrane → simultaneous appearance of reflected wavefronts (in water, same center) and transmitted wavefronts (in oil, same center, lower contrast/slower). [Phase 5] Sustained behavior: membrane stays intact and in place, no mixing between water and oil, no spontaneous wave generation in the oil; all motion observed from fixed frontal viewpoint with full visibility of channel width and membrane boundary length.

Manual:
Experimental Procedure
1. Fill a transparent rectangular channel with water on the left half and oil on the right half; separate the two with a thin, taut, flexible, watertight membrane that spans the full depth and width of the channel, forming a straight vertical boundary that keeps the liquids from mixing while still letting wave-induced surface displacement pass through it.
2. Place a point source at the water side, near the center of the water region, and activate it to generate circular waves.
3. Observe wave propagation from the source toward the membrane boundary and how it affects the waves on both sides.
Observation of Experimental Phenomena
- Circular wavefronts originate from the point source in water and travel radially outward.
- Upon reaching the membrane boundary, part of the wave reflects back into the water as circular wavefronts centered on the source.
- Part of the wave transmits through the membrane into the oil as slower, lower-contrast circular wavefronts, still centered on the source.
- Water and oil stay visibly separated by the membrane and never mix: water appears clearer and more reflective; oil appears more opaque and less reflective.
Summary of Experimental Principles
In each liquid, the surface wave's propagation speed and amplitude depend on the liquid's density and depth; because water and oil differ in density, they load the flexible membrane unevenly as it flexes with each incoming wave, producing a wave-impedance mismatch at the boundary that sends part of the wave's energy back into the water (reflection) and lets part of it continue into the oil (transmission) at reduced amplitude and speed; conservation of wave energy and Huygens' principle explain why the circular wavefront shape and center are preserved through both reflection and transmission.

Prompt Grounding rubric:
level_1: No transparent channel with two distinct liquid regions is visible; water and/or oil is missing, or a straight boundary/membrane between them cannot be seen; no point source appears anywhere in the scene; no circular wave pattern radiates outward from any point.
level_2: A channel is shown but the water–oil setup is incomplete: either water or oil is missing, or the two liquids cannot be visually told apart; the boundary between them is curved, gapped, or not visible as one continuous line; a point source may be present but produces no visible waves, or the resulting pattern is not circular (e.g., straight ripples, a single splash, or irregular ripples).
level_3: Water and oil occupy two side-by-side regions of the channel, divided by a straight, continuous boundary line (the membrane) that runs the full depth and width of the channel; a point source sits on the water side and emits circular wavefronts that expand outward; the wavefronts have not yet visibly reached the boundary.
level_4: Everything in score 3 is shown, and the circular wavefronts also visibly travel across the water and make contact with the boundary; the boundary line stays straight, unbroken, and in the same position throughout the sequence; water and oil keep their side-by-side positions, with neither liquid crossing into the other's region, mixing, or disappearing from frame.
level_5: Everything in score 4 is shown, and the point source sits only within the water region, never in the oil or exactly on the boundary line; every wavefront originates in the water and moves toward the boundary, with no independent wave activity starting on the oil side before contact; the boundary line stays straight and continuous along its entire visible length in every frame.

Scientific and Causal Correctness rubric:
level_1: Water and oil respond to the waves identically (crossing the boundary produces no change in speed, amplitude, or shape, as if no membrane or boundary were there at all); or, at the opposite extreme, the wave stops completely and nothing ever enters the oil; alternatively, water and oil cannot be visually told apart in the first place.
level_2: Water and oil are visually distinguishable (e.g., by color or clarity), but wavefronts cross the boundary with no visible reflection back into the water and no visible reduction in amplitude or slowdown once continuing into the oil; the boundary appears to have no effect on the waves crossing it.
level_3: Water and oil are visually distinguishable; as the outward-moving wavefronts in water reach the boundary, a second set of circular wavefronts appears moving back into the water (reflection), centered on the point source; at the same time, a set of wavefronts appears in the oil (transmission), also circular and centered on the source, though dimmer or less sharply defined than the wavefronts in the water.
level_4: Everything in score 3 holds, and the transmitted wavefronts in the oil are clearly weaker and slower-moving than their counterparts in the water (lower amplitude and reduced contrast), while the reflected wavefronts in the water keep their circular shape and stay centered on the point source; no wave activity appears in the oil independently of, or ahead of, the transmission arriving from the water side.
level_5: Everything in score 4 holds, and the reflected wavefronts stay fully circular and centered exactly on the point source; the transmitted wavefronts in the oil are visibly circular with crests spaced more closely together (consistent with a shorter wavelength and slower speed) and noticeably lower contrast than in the water; the wavefronts do not bend or split as they cross the boundary, and no wave energy appears on the oil side before the corresponding wavefront actually reaches the boundary.

Spatiotemporal Consistency rubric:
level_1: The membrane boundary jumps to a different position or flickers in and out between frames; water and oil merge together or one of them disappears mid-sequence; the point source appears or disappears without explanation; wavefronts jump from one position to another or reverse direction outright; the overall brightness of the scene changes abruptly in a way unrelated to the wave motion.
level_2: The boundary is mostly straight but shows occasional waviness or small gaps that come and go; the water and/or oil flicker in transparency or shift slightly relative to each other between frames; wavefronts occasionally skip ahead, stutter, or momentarily lose their circular shape; the point source drifts sideways while emitting waves.
level_3: The boundary stays straight and fixed in place; water and oil hold their positions relative to each other and to the channel walls; the point source stays in one spot; wavefronts expand outward from the source smoothly and continuously, with no jump in position, no sudden gap, and no tearing of the boundary line.
level_4: Everything in score 3 holds, and every wavefront also keeps a consistent circular shape and shared center as it expands, with no warping, stretching, or pinching as it nears the boundary; highlights and reflections on the water and oil surfaces shift smoothly together with the wave motion rather than jumping or changing tone all at once; the boundary and both liquid regions stay aligned from frame to frame with no visible drift.
level_5: Everything in score 4 holds, and the wavefront edges also stay smooth and continuous as they travel, with no jagged stepping, flicker, or shimmer along the crests; the boundary shows a consistently sharp, clean separation between water and oil with no blurring or bleeding between the two liquids; the timing of the wave motion (its expansion speed and the slowdown as it crosses into the oil) stays smooth and consistent, with no mismatched acceleration or sudden jumps between the wavefronts and the rest of the scene.