Domain: Humanities and Social Sciences — Economics
Target concept: Demand curve characteristics: A curve that slopes downward from left to right.

Video generation prompt: Plot the axes: the vertical axis represents price, and the horizontal axis represents quantity. Plot multiple price-quantity points, where price varies with demand, and smoothly connect these points to form a curve. Use clear labels and plot in sequence.

Evaluation guide:
Target concept: Demand curve as a downward-sloping graphical representation of the inverse price–quantity relationship under ceteris paribus. Minimum mechanistic assumptions: (i) price is exogenous and controls quantity demanded; (ii) all other determinants (income, preferences, substitutes) are held constant; (iii) plotting follows strict Cartesian convention (price=y, quantity=x). Phased storyline: (1) Axes materialize with correct orientation and labels; (2) Points appear sequentially from high-price/low-quantity (upper-left) to low-price/high-quantity (lower-right); (3) A single smooth curve draws in real-time connecting them in order; (4) Final static frame confirms monotonic downward slope. Visibility constraints: Must be legible at 10s duration; all labels and points ≥12pt equivalent; curve stroke ≥3px; no occlusion or motion blur; verification requires side-by-side comparison of leftmost vs. rightmost y-coordinates on a fixed x-scale.

Manual:
I. Basic Demonstration Information
Demonstration Title: Demand Curve Characteristics (Downward-Sloping Curve) Demonstration
Subject: Humanities and Social Sciences - Economics - Microeconomics
Demonstration Purpose: To visually demonstrate that the demand curve slopes downward from left to right, reflecting the inverse relationship between price and quantity demanded; to reinforce correct axis conventions (price on vertical axis, quantity on horizontal axis); and to practice accurate plotting and smooth curve connection of price-quantity data points.

II. Demonstration Carrier/Equipment
Core Carrier: Digital graphing interface (clean white background, scalable coordinate grid)
Auxiliary Equipment: High-contrast vector-based plotting tools; dynamic labeling engine; sequential point-drawing animation controller.

III. Demonstration Content Description
Layout: Centered Cartesian plane occupying ≥80% of screen; origin at bottom-left; y-axis labeled ‘Price’ (top-aligned, bold, black), x-axis labeled ‘Quantity Demanded’ (right-aligned, bold, black); both axes include evenly spaced tick marks and numeric values.
State Control: All elements rendered statically after animation completes; no interactive or real-time input; animation runs once, linearly, within 10 seconds.
Sequence: (1) Axes appear instantly; (2) Six price-quantity points plot sequentially left-to-right (i.e., increasing quantity): (P₁,Q₁)→(P₂,Q₂)→…→(P₆,Q₆), where P₁>P₂>…>P₆ and Q₁<Q₂<…<Q₆; (3) After final point appears, a smooth, continuous curve draws from (P₁,Q₁) to (P₆,Q₆) without lifting; (4) Final frame holds for 1.5 seconds with full curve, labeled axes, and no distractions.

IV. Observation of Core Phenomena
Expected Phenomenon: A clearly downward-sloping curve extending from upper-left to lower-right.
Expected Screen: Clean, minimal, high-contrast 2D graph — no legends, titles, colors beyond black/gray, or decorative elements.
Visual Verification Features: (a) Vertical axis = Price, horizontal axis = Quantity Demanded; (b) At least six distinct points plotted in descending price / ascending quantity order; (c) Points smoothly and exclusively connected by one continuous line; (d) Line consistently descends — every rightward movement along x-axis corresponds to downward movement along y-axis; (e) No flat, upward, or segmented deviations.

V. Summary of Key Knowledge Points and Principles
Core Concept Definition: The demand curve is a graphical representation of the inverse relationship between the price of a good and the quantity consumers are willing and able to purchase, ceteris paribus.
Principle of Visual Feature Recognition: Downward slope is the defining visual signature — verified by comparing relative vertical positions of points sharing increasing horizontal (quantity) coordinates. Leftmost point must be highest; rightmost point must be lowest; intermediate points must follow monotonic descent.

VI. Demonstration Precautions
- Avoid any animation that implies supply, elasticity, shifts, or external factors (e.g., income change).
- Do not use color gradients, 3D effects, or moving labels — maintain strict 2D orthographic projection.
- Ensure all numeric labels are integers or simple decimals (e.g., 10, 20, 30 or 10.0, 20.0); avoid scientific notation or truncation.
- Curve must be mathematically monotonic decreasing over its displayed domain — no local minima/maxima.

Prompt Grounding rubric:
level_1: No coordinate axes are drawn; there are no 'Price' or 'Quantity' labels anywhere; no data points are plotted; there is no downward-sloping curve; the screen instead shows something unrelated such as a bar chart, an upward-sloping line, or plain text.
level_2: Axes are drawn but mislabeled or unlabeled: for example 'Price' is placed on the horizontal axis and 'Quantity' on the vertical axis, or neither axis has a label; only one or two points are plotted with no line connecting them; if any curve appears it slopes upward rather than downward.
level_3: Price is correctly placed on the vertical axis and Quantity on the horizontal axis, and both are labeled, though the labels are small, crowded, or hard to read; three to four price-quantity points are plotted, but the connecting line is jagged, has visible breaks, or the overall downward trend is interrupted by an upward kink.
level_4: Axes are clearly and correctly labeled ('Price' on the vertical axis, 'Quantity' on the horizontal axis); at least five points are plotted, each showing a lower price paired with a higher quantity than the point before it; the points are joined into one continuous, smoothly curving downward line; any imperfection is minor, such as a slightly crooked label or a small wobble in the curve.
level_5: All conditions of score 4 are met; the plane shows six clearly marked points at coordinates (Quantity, Price) equal to (10,100), (20,85), (30,70), (40,50), (50,30), (60,15), each showing rising quantity paired with falling price moving left to right; the points are joined by one single, unbroken, downward-curving line with no gaps or corrections; the screen has nothing else on it (no legend, no title, no extra annotation) and stays sharp and easy to read for the full ten seconds.

Scientific and Causal Correctness rubric:
level_1: The line slopes upward or is flat rather than downward; some points show a higher price paired with a higher quantity, violating the law of demand; the axis labels are swapped or wrong (e.g., 'Supply' used instead of 'Demand').
level_2: Axis labels use the right economic terms, but a point pair or the plotting order contradicts the inverse price-quantity relationship: for example a low-price point is drawn before a high-price point even though the line still slopes downward overall; nothing about the order in which points appear indicates that price and quantity move oppositely.
level_3: Every plotted point is consistent with the law of demand (as price falls, quantity rises) and the axes are labeled correctly; however all six points seem to appear at once rather than one at a time, so there is no visible ordering that lets a viewer confirm the points were plotted from high-price/low-quantity toward low-price/high-quantity.
level_4: All conditions of score 3 are met; points appear one after another, moving from the highest-price/lowest-quantity point first to the lowest-price/highest-quantity point last; the connecting curve extends farther across the plane after each new point appears, so its downward path visibly builds up in the same order the points were added.
level_5: All conditions of score 4 are met; the six points are spaced so each successive point sits both further right (higher quantity) and further down (lower price) than the one before it, with no reversals; the curve's downward path finishes only after the final, lowest-price/highest-quantity point has appeared, so the complete curve visibly traces the whole inverse price-quantity relationship end to end; the plane contains nothing beyond the axes, points, and curve; no added color coding, arrows, or text callouts are needed to convey the relationship.

Spatiotemporal Consistency rubric:
level_1: Axes are drawn crooked or don't meet at a clean corner; points float away from the grid lines; the curve detaches from the points it is supposed to connect or bends unnaturally as if viewed at an angle; a point appears, disappears, and comes back; playback stutters or visibly skips.
level_2: Axes are aligned but one is stretched or squeezed relative to the other; points wobble or shift position slightly after being placed; the curve appears to redraw itself partway through rather than being added once; the line's thickness or opacity changes between frames; there is a noticeable pause of half a second or more between a point appearing and the curve reaching it.
level_3: Axes stay straight and perpendicular to each other; once a point is placed it stays in that exact spot for the rest of the video; the curve is drawn continuously, with at most a slight change of drawing speed; any gridlines present stay fixed; only a very small inconsistency remains, such as one axis label sitting a little off its tick mark or the curve's end slightly overshooting the last point.
level_4: All conditions of score 3 are met; the axes cross at a consistent origin and each point sits squarely on its intended grid position; the curve visibly threads through every plotted point rather than passing near them; the line keeps a steady thickness and opacity throughout; the point-by-point and curve-drawing animation moves at a steady, even pace with no visible jitter or drift once things are placed.
level_5: All conditions of score 4 are met; the axes remain straight, perpendicular, and reach the edges of the frame with evenly spaced tick marks for the whole ten seconds; each point locks into its coordinate the moment it appears and never drifts afterward; the curve is drawn as one continuous stroke that visibly speeds up through the middle and slows near the last point, matching a natural drawing motion; lighting and contrast of the whole graph stay even for the entire clip, with no dropped frames, sudden jumps, or unexplained changes in the size of the graph.