Domain: Humanities and Social Sciences — Geography
Target concept: Mechanical Weathering: Spherical weathering of rocks in African deserts (rounded rocks with smooth surfaces) and angular weathering of rocks in Asian mountainous regions (angular rocks with rough surfaces)

Video generation prompt: Place a spherical weathered rock labeled African Desert next to a angular weathered rock labeled Asian Mountain. During the photography, focus on capturing the surface roughness and morphology of both rocks.

Evaluation guide:
Target concept: Mechanical weathering manifests as divergent rock morphologies due to regional differences in dominant physical stresses: spherical weathering arises from isotropic insolation-driven exfoliation in arid deserts, while angular weathering arises from anisotropic freeze-thaw or tectonic stress along joints in mountainous regions. Minimum mechanistic assumptions: (1) rock composition is similar (e.g., felsic igneous), eliminating lithology as confounder; (2) weathering is purely mechanical (no chemical dissolution or biological involvement); (3) surface texture directly records dominant erosion agent (wind abrasion vs. ice wedging). Phased storyline: [Phase 1: Static setup] Two rocks placed side-by-side on neutral background with scale ruler and location-specific labels. [Phase 2: Visual verification] Camera holds fixed frame; raking light illuminates both: spherical rock shows diffuse reflection and soft contour, angular rock shows sharp shadow lines and grain relief. [Phase 3: Causal confirmation] Labels are not decorative but index real-world processes: "African Desert" implies thermal expansion/contraction + salt crystallization → rounding; "Asian Mountain" implies water infiltration into joints + freezing → shattering. Visibility constraints: Both the fine surface grain (rough/granular vs. smooth/polished) and the overall rock outline (rounded vs. sharply cornered: the rounded rock's surface should curve with no edge sharper than roughly 15°, while the angular rock's corners should meet at roughly 60° or less) must be clearly distinguishable to an ordinary viewer at normal screen viewing distance, achieved through close framing, raking side-light, and enough depth of field that both rocks stay in focus from edge to edge. Perspective must be orthographic or near-orthographic to prevent foreshortening distortion of angles or curvature.

Manual:
I. Basic Demonstration Information
Demonstration Title: Mechanical Weathering: Spherical vs. Angular Rock Morphology Comparison (African Desert vs. Asian Mountain)
Subject: Geography - Physical Geography - Weathering Processes
Demonstration Purpose: By placing a spherical weathered rock labeled "African Desert" next to an angular weathered rock labeled "Asian Mountain", this demonstration visually contrasts two end-member styles of mechanical weathering — spheroidal (dominant in arid, insolation-rich deserts) and joint-controlled angular (dominant in cold, tectonically active mountains); it enables recognition of surface roughness and morphological signatures as diagnostic visual proxies for weathering environment and process.
II. Demonstration Carrier/Equipment
Core Carrier: Two natural rock specimens — (1) a spheroidal granite corestone (sub-rounded to ellipsoidal, diameter 8–12 cm, smooth, laminated surface) labeled "African Desert"; (2) an angular basalt or schist fragment (polyhedral, ≥3 sharp edges, 8–12 cm longest dimension, granular/etched surface) labeled "Asian Mountain".
Auxiliary Equipment: Neutral gray matte background board (60×40 cm), fixed tripod-mounted DSLR/mirrorless camera with macro lens (≥1:1 magnification), directional LED lamp (45° left-top, 5600K), ruler (10 cm, placed horizontally between rocks for scale reference), label tags (black sans-serif font on white adhesive backing, 2.5 cm × 1 cm).
III. Demonstration Content Description
Layout: Place background board flat on stable surface. Position spherical rock on left, angular rock on right, 1.5 cm apart center-to-center. Align both rocks’ longest axes parallel to bottom edge of frame. Place ruler horizontally touching outer edges of both rocks. Affix labels directly beneath respective rocks, centered, 0.3 cm below base contact line.
State Control: Ensure rock surfaces are dry and dust-free (use soft brush if needed); avoid fingerprints or moisture. No handling during capture.
Comparison Baseline: Specimens matched for approximate size (±0.5 cm in maximum dimension) and mineralogical homogeneity (no veining or staining that distracts from texture/morphology).
IV. Observation of Core Phenomena
Spherical Rock (African Desert) Characteristics: Dominant convex curvature; no visible edges or facets; surface is optically smooth with subtle concentric exfoliation ridges; texture appears fine-grained, homogeneous, and wind-abraded; no exposed fractures or angular protrusions.
Angular Rock (Asian Mountain) Characteristics: Distinct straight edges and flat mineralogical facets; ≥3 acute angles (<60°); surface exhibits coarse grain relief, micro-fractures, and pitting from freeze-thaw cycles; texture is visibly rough, granular, and unpolished.
Morpho-Textural Contrast: Under raking light, spherical rock reflects light uniformly with soft highlight; angular rock casts sharp, high-contrast shadows in fissures and along edges — confirming differential response to mechanical stress.
Label Integrity: Both labels are fully legible, correctly assigned, and geometrically aligned — no rotation, skew, or occlusion.
V. Summary of Key Knowledge Points and Principles
Core Concept Definition: Mechanical weathering is the physical disintegration of bedrock without chemical change; spherical weathering results from repeated diurnal thermal expansion and contraction of the rock's outer shell (insolation weathering) combined with salt-crystal growth in surface pores and wind-driven sand abrasion, which together wear down corners and edges faster than flat faces and cause the outer, concentrically weakened layer to spall off in stable, arid settings; angular weathering results from preferential fracturing along pre-existing joints under cyclic freeze-thaw or stress release in tectonically active, high-relief terrain.
Geomorphic Significance:
— Spherical forms indicate long-term, low-energy, insolation-dominated regimes (e.g., Sahara granite inselbergs).
— Angular forms indicate recent, high-energy, cryogenic or tectonic regimes (e.g., Himalayan scree slopes).
— Surface roughness is a direct proxy: smooth = prolonged abrasion + outer-layer removal; rough = fresh fracture + minimal transport smoothing.
VI. Demonstration Precautions
Specimen Authenticity: Use naturally weathered field-collected specimens — no artificial grinding, polishing, or sculpting. Confirm provenance: spherical rock must originate from documented desert corestone locality (e.g., Namib); angular rock from documented alpine joint-block deposit (e.g., Tibetan Plateau).
Imaging Fidelity: Use manual focus and exposure; disable auto-white-balance (set to 5600K); shoot RAW + JPEG; frame fills 80% of sensor height with rocks and ruler; no post-processing beyond cropping and level adjustment.

Prompt Grounding rubric:
level_1: No rocks are visible, or only one rock appears, or both rocks share the same shape (both rounded or both angular), or neither rock has a location label attached, or a label sits next to the wrong rock (e.g. "African Desert" attached to the angular rock), or the surface texture of the rocks cannot be seen at all because of blur, occlusion, or completely flat lighting.
level_2: Both rocks are present with labels attached, but a label is unreadable, floating away from its rock, or attached to the wrong rock; one rock's shape roughly matches its label (rounded vs. angular) while the other is ambiguous (e.g., mostly rounded but still showing a few sharp corners, or mostly angular but with its corners visibly worn down); any difference in surface roughness between the two rocks is barely hinted at and hard to confirm by eye.
level_3: Two clearly different rocks sit side by side: one dominated by smooth, curved surfaces with no straight edges, labeled "African Desert", the other dominated by flat faces meeting at sharp corners, labeled "Asian Mountain"; both labels are legible and attached to the correct rock; a difference in surface texture (smoother vs. grainier) can be seen, but lighting or focus keeps it from being fully clear across the whole rock surface.
level_4: The two rocks sit close together (touching or with only a small gap, less than about 2 cm) with correctly attached labels of matching font size, placed at the same height beneath each rock; the rounded rock shows continuous curves with no flat segments or sharp corners anywhere on its visible surface and a uniformly smooth texture; the angular rock shows at least three distinct flat faces meeting at sharp corners and a visibly grainy, rough texture; side-lighting brings out this contrast (soft highlights on the curves, hard shadow lines in the angular rock's corners); nothing else in the frame obscures either rock's shape or its label.
level_5: The rounded rock reads unmistakably as dome- or egg-shaped with a continuously smooth surface: no pits, cracks, or flat segments anywhere on it; the angular rock reads unmistakably as a block with flat mineral faces, crisp sharp corners, and a visibly coarse, grainy surface; both labels are clean, legible, evenly sized, placed at the same height directly beneath their rock, and use the same font and color treatment; the rounded rock sits on the left and the angular rock on the right, matching their labels; each label's height looks proportionate to the rock above it (roughly 15% of the rock's height, clearly readable, neither tiny nor oversized) and is centered under that rock; both the fine grain of the rough rock and the smooth sheen of the rounded rock are visible at once, with no part of either rock out of focus.

Scientific and Causal Correctness rubric:
level_1: The rounded rock shows sharp fractures, flat facets, or exfoliating flakes (features that belong to the angular/joint-controlled rock), or the angular rock instead looks worn smooth and rounded; or the two rocks appear weathered in the same way despite their different labels; nothing in the image ties either rock's shape to its location label.
level_2: The rounded rock is generally roundish and the angular rock generally pointy, but neither shows any texture that would actually be attributed to its named process: no smooth, worn sheen on the rounded rock consistent with long-term abrasion, and no fresh, sharp-edged fracture faces on the angular rock consistent with recent jointing; the labels read as arbitrary captions rather than tied to a visible weathering signature.
level_3: The rounded rock's continuous curvature is consistent with a rock whose corners and edges have worn away faster than its flat faces (the expected outcome of desert heat-cycling, salt growth, and sandblasting); the angular rock's straight edges and flat faces are consistent with breaking along pre-existing joint planes (the expected outcome of repeated freeze-thaw in a mountain setting); but neither rock shows the surface-roughness contrast (smooth vs. grainy) that would confirm which process dominated.
level_4: The rounded rock shows a uniformly smooth, worn surface with no remaining flat segments anywhere, consistent with prolonged thermal-cycling and wind-driven sand abrasion rounding off every corner; the angular rock shows fresh-looking flat faces, sharp corners, and a visibly grainy surface with loose grit or small debris scattered at its base, consistent with recent frost-driven fracturing along joints; but the link between the two rocks and their labeled locations ("African Desert" implying heat-cycling and sand abrasion, "Asian Mountain" implying freeze-thaw jointing) is not made obvious by anything else visible in the frame, such as the raking light failing to contrast the two surfaces.
level_5: The rounded rock's smooth, corner-free surface and the angular rock's sharp, flat-faced surface visually explain their labels without needing a caption: the rounded rock looks evenly worn down from every direction, matching a desert environment of heat-cycling and windblown sand, while the angular rock looks freshly broken along flat joint planes, matching a mountain environment of repeated freezing and thawing, with loose angular chips resting at its base; under the raking light, the rounded rock shows a smooth gradient of brightness across its curve while the angular rock shows a hard-edged shadow line at every corner, visually confirming that one surface has been continuously worn and the other has been freshly fractured.

Spatiotemporal Consistency rubric:
level_1: A rock appears to float above the surface, overlap the other rock in an impossible way, or change size dramatically between moments (e.g., the angular rock suddenly looks far larger than the rounded rock); the shot cuts abruptly or flickers; the lighting direction changes partway through; the camera view jumps or zooms erratically rather than holding still.
level_2: The two rocks stay next to each other, but the camera angle looks different for each, e.g., the rounded rock is shown straight-on while the angular rock is shown from a steep side angle in the same shot; the shadows on the two rocks point in different directions as if lit from two different sources; a label appears only after the rock detail has already gone out of focus, or the whole frame blurs and re-sharpens without any visible cause.
level_3: The camera holds a steady, level view of both rocks together from a consistent angle, under even lighting, with both rocks appearing to sit on the same surface plane; one small inconsistency is visible (for example, one rock stays slightly sharper in focus than the other throughout), but nothing else in the frame drifts, flickers, or changes over the course of the video.
level_4: Both rocks stay on the same visible ground plane with no depth mismatch between them; the light comes from one consistent direction the entire time, casting a soft, long shadow beneath the rounded rock's curve and a short, hard-edged shadow at the angular rock's corners, and neither shadow changes direction or length as the video plays; both labels stay in place and the same size as each other for the whole clip; there is no camera movement, no shift in focus, and no visible change in overall brightness at any point.
level_5: The camera view of both rocks together never changes for the whole video: same framing, same angle, same distance; both rocks stay in sharp focus from their highest point to where they meet the surface, with no part of either rock going soft or blurry; the lighting looks identical in the very last frame as in the very first, with no flicker, no shift in shadow position, and no change in overall exposure; there is no visible lens distortion (no bent-looking edges, no dark corners) anywhere that would make the scene look like separate stitched-together shots rather than one continuous take.