Domain: Natural Science — Physics
Target concept: A pendulum swinging in air versus a pendulum with amplitude decreasing over time in a viscous fluid

Video generation prompt: Two identical pendulums are released from the same angle at the same time: one oscillates in air, and the other is immersed in a transparent container filled with viscous oil, displayed side by side.

Evaluation guide:
(i) Target concept: Viscous damping causes exponential amplitude decay in oscillatory systems, contrasting with near-conservative behavior in low-drag media.
Minimum mechanism: Fluid must exert a velocity-dependent resistive (viscous drag) force strong enough to measurably shrink the pendulum's swing amplitude on every half-cycle while the system stays underdamped, so oscillation continues (with progressively shrinking peaks) across several cycles rather than stopping after one swing; pendulum geometry and density must allow full submersion without buoyant instability; suspension must be rigid and effectively frictionless at the pivot.
(ii)Storyline: [Frame 0] Both pendulums held stationary at identical elevated angles beside each other; container fully visible with calm fluid surface. [Release event] Both bobs depart simultaneously from rest with identical angular acceleration onset. [Cycle 1] Air pendulum reaches full opposite angle; viscous pendulum falls short and returns slower. [Cycle 2–3] Air pendulum repeats near-identical arcs; viscous pendulum’s peak displacement visibly declines each half-cycle. [Final state] Viscous pendulum nears rest at equilibrium; air pendulum remains in vigorous motion. Perspective: fixed frontal view, centered on shared horizontal axis, no occlusion, full visibility of both bobs and container fluid level throughout.

Manual:
Experimental Procedure
1. Mount two identical pendulums side by side: one freely suspended in air, the other fully immersed in a tall transparent container filled with viscous oil.
2. Simultaneously release both pendulums from the same initial angle.
Observation of Experimental Phenomena
- Pendulum in air sustains large, nearly constant-amplitude swings.
- Pendulum in viscous oil shows immediate and progressive reduction in swing amplitude; each successive swing is smaller than the prior, with no return to initial angle.
Summary of Experimental Principles
- In air, drag is negligible → energy loss minimal → sustained oscillation.
- In viscous fluid, drag force ∝ velocity → rapid kinetic energy dissipation → exponential amplitude decay.

Prompt Grounding rubric:
level_1: Only one pendulum is shown, or the two pendulums are not placed side by side; the container is missing, opaque, or clearly holds a non-viscous liquid such as plain water; the two pendulums differ visibly in length, bob size, or material; or the two are not released from the same angle at the same moment.
level_2: The side-by-side layout is present, but at least one element is wrong: the container's fluid does not look thick or viscous (e.g., it looks like plain water), or the two pendulum bobs/rods differ noticeably in size or shape, or one pendulum is clearly released well before the other, or the two starting angles are visibly different from each other.
level_3: Two visually matching pendulums are shown side by side: one swinging freely in air, the other fully submerged in a transparent container of a thick, honey- or oil-like fluid; both are pulled to the same starting angle and let go at the same moment.
level_4: Everything at the 3-point level holds, and in addition the container walls are rigid and undistorted, both bobs are solid and evenly colored, the two suspension points sit at the same height and stay fixed, nothing blocks either pendulum from view, and the camera framing stays constant.
level_5: Everything at the 4-point level holds, and in addition the two pendulums are visually identical in every respect (size, shape, color, surface finish), the fluid's surface where the rod passes through it looks believable without distorting the rod or bob, the suspension rods hang straight and parallel to each other, and the two releases happen at the same instant with no visible lag between them.

Scientific and Causal Correctness rubric:
level_1: There is no meaningful contrast between the two pendulums' motion: both swing the same way with no amplitude loss, or one stops dead right after release, or the oil-submerged pendulum keeps swinging at full amplitude while the air pendulum is the one that visibly loses amplitude, reversing which pendulum should be damped.
level_2: A contrast exists but breaks the expected physics: the oil-submerged pendulum swings faster or wider than the air pendulum, or the air pendulum is the one that visibly slows down while the oil-submerged one holds a constant swing, or amplitude loss in the oil only becomes visible several swings in rather than from the very first swing, or the fluid shows no visible resistance to the bob's motion.
level_3: The air pendulum keeps swinging with a large, roughly constant amplitude across the whole clip; the oil-submerged pendulum's swing amplitude visibly shrinks starting from its very first return swing, and it never swings back up to its original starting angle again.
level_4: Everything at the 3-point level holds, and in addition the oil-submerged pendulum's slowdown looks smooth and gradual rather than jerky, sticking, or stopping abruptly; the air pendulum shows no noticeable loss of swing height over the clip; both pendulums keep swinging in the same flat plane without twisting sideways.
level_5: Everything at the 4-point level holds, and in addition the oil-submerged pendulum's swing height gets smaller with every successive swing (never larger than the one before it), the air pendulum's swings stay symmetric about the vertical rest position, and at no point does the oil-submerged pendulum swing higher than the air pendulum's current swing height.

Spatiotemporal Consistency rubric:
level_1: A pendulum bob or rod jumps to a new position with no visible path getting there, the rod detaches from its pivot, the container blinks out or reappears, the camera suddenly pans, zooms, or rotates, or the lighting on the scene changes abruptly (e.g., a shadow disappears and then snaps back).
level_2: A bob's motion freezes for a couple of frames then resumes, the container's edge ripples or warps unnaturally, a suspension point visibly wobbles or seems to float free of its mount, or the shadow cast by a bob shifts in a way that does not match the fixed light source and the bob's own motion.
level_3: Both pendulum rods stay rigid and connected to their pivots throughout, both bobs trace smooth curved paths rather than jumping, the container walls stay flat and unchanging, and the shadows cast by the bobs shift gradually and in step with each bob's own swinging motion rather than flickering or jumping independently.
level_4: Everything at the 3-point level holds, and in addition neither bob changes shape while swinging (staying round or oval rather than stretching or flattening), the two pendulums keep a consistent size and perspective relative to each other and to the shared horizon line, and fast parts of the swing do not visibly skip or strobe.
level_5: Everything at the 4-point level holds, and in addition both bobs' swinging speed changes smoothly with no sudden jump in speed at the top or bottom of a swing, the fluid surface in the container stays essentially flat and undisturbed apart from a small curve where the rod passes through it, and the shadows cast by both pendulums shift continuously and proportionally to each bob's changing angle.