Domain: Humanities and Social Sciences — Economics
Target concept: Characteristics of the law of demand: When the price increases, the quantity demanded moves upward and to the left along the curve.

Video generation prompt: A coordinate axis is displayed on the screen, with the horizontal axis representing quantity demanded and the vertical axis representing price, showing a demand curve. Given a point A on the demand curve, when the price increases, point A will move to point B. Please indicate the position of point B.

Evaluation guide:
Target concept: Law of demand, inverse relationship between price and quantity demanded, visualized as movement *along* a static downward-sloping demand curve. Minimum mechanistic assumptions: (i) ceteris paribus (no other determinants change); (ii) demand curve is exogenously fixed; (iii) price is the sole independent variable driving movement. Expected phenomenon storyline: (Phase 1) Stable frame: labeled point A on downward-sloping demand curve. (Phase 2) Causal trigger: unambiguous price-increase signal localized to vertical axis. (Phase 3) Consequent motion: point A smoothly relocates *only along the curve* to new position B, with strict upward (↑P) and leftward (←Q) displacement. (Phase 4) Stable outcome: point B held in place, confirming final state obeys Q₂ < Q₁ ∧ P₂ > P₁ ∧ B ∈ same curve. Visibility constraints: All elements must be legible at 720p resolution; no occlusion; axis labels and point markers must contrast strongly against white background; motion must be slow enough to track (≥3s traversal) yet fit within 10s limit.

Manual:
I. Basic Demonstration Information
Demonstration Title: Law of Demand — Price Increase Induces Movement Along the Demand Curve
Subject: Economics - Microeconomics - Consumer Theory
Demonstration Purpose: To visually demonstrate that, holding all else constant, an increase in price causes quantity demanded to decrease — resulting in upward-and-leftward movement *along* a given downward-sloping demand curve; to reinforce the distinction between movement along vs. shift of the curve; and to train precise interpretation of coordinate geometry in economic modeling.

II. Demonstration Carrier/Equipment
Core Carrier: Static/dynamic 2D coordinate plane rendered digitally (no physical equipment).
Auxiliary Elements: Clean white background; sans-serif bold fonts; red circular markers for points; black smooth demand curve; upward double-arrow icon on vertical axis; minimal annotations only.

III. Demonstration Content Description
Layout: Full-screen Cartesian plane. Horizontal axis labeled ‘Quantity Demanded’ (centered below x-axis). Vertical axis labeled ‘Price’ (centered left of y-axis, rotated 90°). Origin at bottom-left corner. Downward-sloping demand curve drawn from upper-left to lower-right quadrant (first quadrant only).
State Control: Initial state shows point A (filled red circle, radius 6px) placed at (Q₁, P₁) on the curve. After 2s, an animated upward double-arrow (blue, pulsing) appears beside y-axis with text ‘Price ↑’. Over next 4s, point A smoothly traverses the demand curve to point B at (Q₂, P₂), where Q₂ < Q₁ and P₂ > P₁. Final state holds point B (same red circle) with label ‘B’ for 2s.
Comparison Baseline: No other curves, supply lines, or distractors. Only one demand curve. Axis scales are linear and proportional (1 unit x = 1 unit y in display ratio) to preserve geometric intuition.

IV. Observation of Core Phenomena
Initial Point A: Red circle located on demand curve, with numeric coordinates optionally shown nearby (e.g., ‘A: Q=8, P=4’).
Price Increase Cue: Clear, localized visual signal exclusively on vertical axis — upward arrow + ‘Price ↑’ — no change to curve shape or position.
Point B Position: Red circle appears *on the same demand curve*, strictly higher in price (↑y) and lower in quantity (←x) than A. Measurable offset: Δy > 0, Δx < 0, and B lies on curve (verified by visual continuity and absence of gap).
Movement Path: Smooth, continuous, monotonic trajectory confined entirely to the demand curve — no looping, no deviation, no teleportation.

V. Summary of Key Knowledge Points and Principles
Core Concept Definition: The law of demand states that, ceteris paribus, quantity demanded varies inversely with price — represented graphically as downward-sloping demand curve. A price change causes *movement along* (not shift of) the curve.
Principle of Visual Feature Recognition: Upward-and-leftward displacement of a labeled point *along a fixed downward-sloping line/curve* is the definitive visual signature of price-induced change in quantity demanded. Any vertical-only, horizontal-only, or off-curve movement violates the law.

VI. Demonstration Precautions
- Never animate curve deformation (e.g., pivoting, stretching) — curve must remain static.
- Never introduce supply curve, equilibrium, or external factors (income, preferences) — isolate single-variable causality.
- Labels ‘A’ and ‘B’ must be legible, consistently sized, and placed adjacent (not overlapping) to their respective points.
- Total duration ≤10 seconds: 2s (A static), 3s (cue + reaction onset), 4s (A→B motion), 1s (B static).

Prompt Grounding rubric:
level_1: No coordinate plane appears, or no demand curve is drawn, or point A/point B are never labeled; the axes are mislabeled so that price sits on the horizontal axis and quantity on the vertical axis; or the point moves in the wrong direction (down-right) when the price-increase cue appears.
level_2: A coordinate plane and a curve appear, but with major labeling problems: the axes are swapped, or one axis has no title at all, or the labels are too small or faint to read; the curve does not slope downward; point A is shown but point B is missing, or B appears in a random spot rather than up and to the left of A; there is no visible cue (arrow, text, or otherwise) that the price has increased.
level_3: The horizontal axis is clearly titled 'Quantity Demanded' and the vertical axis 'Price'; a downward-sloping curve is drawn; point A sits on the curve and is labeled; a price-increase cue (arrow or text) appears; a second labeled point is shown near the curve, but it is not clearly both higher and further left than A: for instance it sits directly above A at the same quantity, or off to the side away from the curve's own slope.
level_4: All of the above are correct, and point B sits visibly higher (more price) and further left (less quantity) than A, and B lies on the same curve as A; the price-increase cue (e.g., an upward arrow with a 'P↑' label) is unambiguous; minor imperfections are allowed, such as B looking a hair off the curve line, uneven tick-mark spacing, or no numeric values shown on the axes.
level_5: The plane has bold, clearly legible axis titles ('Quantity Demanded' horizontal, 'Price' vertical); the curve is a single smooth downward-sloping line; A is marked with a filled dot and label at a clearly interior point on the curve; the price-increase cue is unmistakable (e.g., a pulsing upward arrow beside the vertical axis with 'ΔP > 0' or similar text); B is marked with its own filled dot and label, sitting squarely on the curve, visibly higher and further left than A.

Scientific and Causal Correctness rubric:
level_1: The point moves to the right or downward, or ends up off the curve entirely, with no visible link between the price-increase cue and the point's movement; the curve slopes upward; or the axis labeled 'Price' is on the horizontal side instead of the vertical.
level_2: The curve slopes downward as expected, but the point only moves straight up (same quantity) or straight sideways (same price) rather than diagonally up-and-left; the price-increase cue and the point's movement appear at the exact same instant with no before/after distinction; the curve has an unexplained kink or corner that isn't just an artistic simplification.
level_3: Point B ends up up and to the left of point A, following the curve's own slope, which is directionally correct; however the causal story is thin: for example the price cue and the movement happen in the same moment rather than cue-then-movement, or nothing on screen explains why the point stays on the curve rather than jumping off it.
level_4: The sequence reads clearly in order: A sits still on the curve, then a visible price-increase cue appears, then A glides along the curve to B, then B holds still; every step matches the law of demand, but the video gives no signal (text, framing, or otherwise) that other conditions are being held constant: for instance nothing rules out the demand curve itself also shifting.
level_5: The full causal chain is visible and unambiguous: A rests on the curve; an explicit, hard-to-miss price-increase cue appears (e.g., an animated arrow next to the price axis paired with on-screen text); the point then travels only along the existing curve to B, with the curve itself never redrawn, tilted, or replaced; the final frame clearly shows B on the same curve, higher in price and lower in quantity than A, with no second curve, no supply-side element, and no other cue suggesting a different cause for the movement.

Spatiotemporal Consistency rubric:
level_1: The two axes do not meet at a single fixed corner: the origin drifts, or the axes appear to cross in more than one place; the demand curve breaks into disconnected pieces, or extends into a region with negative price or negative quantity for no reason; point B sits somewhere off the curve, floating in blank space; point A is shown at one moment and point B is shown at the next with no path ever drawn connecting them; the whole plot jitters or rescales abruptly partway through the clip.
level_2: The origin is placed inconsistently: the axes appear to cross away from the bottom-left corner, or that crossing point shifts partway through the clip; the curve is drawn with visibly different line thickness in different places, or has a broken segment somewhere along its length; point A and point B are rendered as different sizes or colors with no stated reason; the point's path from A to B bends sharply or snaps partway rather than following one continuous track; the motion speeds up, stops, and restarts instead of moving at a steady pace.
level_3: The two axes meet at one fixed origin in the bottom-left corner for the whole clip; the demand curve is a single unbroken line of even thickness; points A and B are drawn with the same marker style (same size, same color); the point travels along one continuous, visibly monotonic path from A's location toward the upper-left to B's location; the motion is roughly steady, though it may start or stop somewhat abruptly rather than easing smoothly in and out.
level_4: Beyond level 3, the curve's downward-sloping shape has no kinks, dips, or bends anywhere along its length, and it looks the same shape at the end of the clip as it did at the start; the moving point's path visibly hugs the curve rather than cutting a straight diagonal line across the plot; the point's motion eases in as it starts and eases out as it settles at B, rather than starting or stopping instantly; the axis titles and the price-increase cue stay the same font size and position throughout.
level_5: Beyond level 4, the camera framing (zoom level and the plot's position on screen) never changes across the whole clip; the point's track along the curve looks like a single smooth arc with no visible stair-stepping or backtracking; the pacing is clearly readable as distinct stages (a brief still moment on A, a visible price-increase cue, an unhurried glide from A to B, a brief still moment on B) with no jarring cut between any of these stages; the curve, axes, and labels look identical in style from the first frame to the last.