Momentum Game!

Game Design Document

Version: 2.1 Final (2025-01-18) • Status: Production Ready
Designer: Guillermo Ithier
Document ID: PTB-GDD-v2.1

Design Overview

Problem: Students conflate force with motion; struggle with ΣF logic and direction mapping.

Solution: A 2-player simultaneous-reveal microgame that turns every card play into a prediction about ΣF. Unbalanced pushes move the block; repeated wins in the same direction simulate “acceleration” via a 2-space streak move.

Core Design Moves:

Simultaneous reveal creates prediction pressure—players must commit before seeing opponent’s choice
Green cards force explicit equilibrium articulation (ΣF = 0 → no motion change)
Streak mechanic externalizes “acceleration” as observable position change

1) Design Pillars

Frictionless world: Only ΣF ≠ 0 changes motion.

Visible acceleration: Consecutive net force in the same direction increases displacement.

Minimal pieces, maximal talk: Each reveal requires a claim about net force and motion.

2) Learning Goals (Teacher-Facing)

Players will:

Distinguish ΣF = 0 vs ΣF ≠ 0 outcomes
Map force direction → acceleration direction → position change
Articulate that constant velocity requires no net force; net force changes motion

3) Components

Component	Specification
Track	0 \| 1 \| 2 \| 3 (start at 1; Red aims for 3, Blue aims for 0)
Block token	1 piece
Streak marker	Arrow indicator (None / → Right / ← Left)
Streak count	Optional d6 set to 0–2, or track verbally

Deck (16 cards):

🔴 Red Push → : 6 cards (3 Dark, 3 Light)
🔵 Blue Push ← : 6 cards (3 Dark, 3 Light)
🟢 Green Stop : 4 cards

4) Win / End Conditions

Immediate win: Block reaches your edge (Red at 3, Blue at 0).

Timed class end: Closest to your edge wins (higher position favors Red; lower favors Blue). Ties: fewer Greens played wins; still tied → draw.

Draw condition: Both players play Green in two consecutive rounds. Game ends after resolving the second such round.

5) Setup (≤60 seconds)

Place block at position 1
Set streak marker to None; streak count to 0
Shuffle deck; deal 3 cards to each player
Place remaining cards face-down as draw pile; leave space for shared discard pile
Determine first player randomly

6) Round Flow

Each round proceeds through these phases in order:

Choose: Each player selects 1 card from hand (secret)
Reveal: Both cards revealed simultaneously
Resolve: Follow §7 Rules in order:

A) Check Green priority
B) Determine Push vs Push outcome
C) Move block per streak rule
D) Update streak record

Discard: Place both revealed cards in shared discard pile
Draw: Each player draws back to 3 cards (reshuffle discard if draw pile empty)
Check End: Win or draw condition met?

7) Rules (Single Source of Truth)

7.1 Card Strength

Light = 1, Dark = 2
Opposite-color Pushes contest: higher strength wins; equal strength ties
Same-color Pushes do not contest: treat as ΣF = 0 (no move); reset streak

7.2 Green Priority

If any Green is revealed:

No movement this round
Reset streak (marker = None; count = 0)
Green overrides all strength comparisons

7.3 Determine Round Outcome (no Green revealed)

Situation	Result
Opposite-color, unequal strength	Higher strength = winner
Opposite-color, equal strength	Tie (no move)
Same-color Pushes	No contest → no move; reset streak

7.4 Movement Rule (when a winner exists)

Define “Last Winner” as the winner of the most recent non-Green, non-tie round. If none exists, treat as “different.”

Condition	Movement
Current winner ≠ Last Winner	Move 1 toward current winner
Current winner = Last Winner	Move 2 toward current winner

Clamp/Overshoot: If movement would pass 0 or 3, place block on the edge and end immediately (win).

7.5 Streak Record

After resolving movement, update the streak record:

Outcome	Streak Marker	Streak Count
Winner = Last Winner	Winner’s direction	2 (cap)
Winner ≠ Last Winner	Winner’s direction	1
Tie, same-color Push, or Green	None	0

Note: The streak count is tracking only—the movement rule in §7.4 handles everything. If you prefer minimal bookkeeping, just track the marker direction and compare winners directly.

8) Worked Examples

Example A: Tie Resets Streak

R1: Red-Dark vs Blue-Light → Red wins → move 1 (1→2). Last Winner = Red.
R2: Red-Light vs Blue-Light → tie → no move; streak reset.

Example B: Streak Produces Double Movement

Start at position 2
R1: Blue-Dark vs Red-Light → Blue wins → move 1 (2→1). Last Winner = Blue.
R2: Blue-Dark vs Red-Light → Blue wins again → move 2 (1→0) → Blue wins.

Example C: Green Overrides and Resets

Block at 2; Last Winner = Red
Blue plays Green vs Red-Dark → no move; streak reset. Position stays 2.

9) Classroom Integration

Table Talk Prompts (Optional)

Before reveal: “Predict ΣF and motion.”
After reveal: “State net force and resulting motion in one sentence.”

Student Referee Role (Optional)

Assign an SR to watch for rule triggers and award reasoning tokens for clean physics articulation.

Quick Rulings

Issue	Resolution
Streak forgotten	Default to no Last Winner (movement = 1 if winner exists)
Empty hand	Draw to 3 immediately (procedural fix)
Reveal dispute	SR may force hesitant card to stand or replay reveal

10) Tuning Notes

4 Greens create frequent ΣF = 0 teachable moments
If games end too fast: Limit 2-move to once per streak chain
If games drag: Add 1 Red-Dark + 1 Blue-Dark (18-card deck)

11) Production Specs

Card faces:

🔴 Red: arrow “→”, label “Push Right”, Dark/Light shade indicator
🔵 Blue: arrow “←”, label “Push Left”, Dark/Light shade indicator
🟢 Green: “STOP / Equilibrium”

Stock: 2.5 × 3.5 in standard cardstock; rounded corners

Board: 3–5 cm wide spaces; large dots under 0 and 3

12) Referee Checklist (Student Card)

Any Green? → No move; set streak marker to None; count = 0
Both Green two rounds in a row? → Draw (game ends)
No Green, opposite colors: who’s stronger? → Winner moves block
Same winner as last non-Green, non-tie round? → Move 2; else move 1
Overshoot edge? → Clamp and declare winner
Hands back to 3; reshuffle if draw pile empty

GDD: Momentum Game!