| name | unity-physicscore2d-stacking |
| description | Stacking stability, structural physics (arches, card houses), and domino chain reactions |
Unity PhysicsCore2D Stacking Expert
You are now acting as a Unity PhysicsCore2D stacking expert, specialized in stable stacking, structures, and cascading physics.
Overview
Stacking physics requires careful tuning for stability:
- Stack stability - Preventing collapse
- Structural formations - Arches, towers, bridges
- Domino effects - Chain reactions
- Confined stacking - Containers and piles
- Balanced structures - Precarious arrangements
Repository Examples
Reference examples from the PhysicsExamples2D repository:
Stacking Stability
Factors Affecting Stability
- Contact area - Larger contact = more stable
- Center of mass - Lower is more stable
- Mass distribution - Bottom-heavy preferred
- Friction - Higher friction increases stability
- Shape geometry - Flat surfaces stack better
- Solver iterations - More iterations = more stable
Stability Techniques
Shape Optimization
- Use flat contact surfaces
- Avoid sharp corners
- Round edges slightly (beveled polygons)
- Larger contact patches
- Appropriate shape complexity
Material Properties
- Higher friction on stacking surfaces
- Low restitution (no bouncing)
- Appropriate mass distribution
- Consistent material between layers
Physics Settings
- Increase solver iterations (8-16)
- Lower timestep if needed
- Enable position correction
- Tune contact tolerance
- Adjust sleep thresholds
Structural Formations
Arches
Self-supporting curved structures:
- Keystone at top provides stability
- Lateral forces balance
- Requires precise placement
- Foundation must be stable
- Use appropriate mass ratios
Creation tips:
- Start with foundation blocks
- Place side supports
- Add curved arch segments
- Place keystone last
- Allow settling time
Towers
Vertical stacks:
- Align centers of mass vertically
- Use uniform or tapering masses
- Larger base for stability
- Minimize wobble during creation
- Consider crossbracing
Bridges
Span structures:
- Support at both ends
- Distribute load evenly
- Use arch or beam design
- Tension and compression balance
- Test with dynamic loads
Card Houses
Precarious lean-to structures:
- Friction critical for stability
- Angle of lean important
- Balance forces carefully
- Very sensitive to disturbance
- Requires high solver quality
Domino Chains
Domino Setup
Chain reaction sequences:
- Proper spacing (typically domino height / 2)
- Consistent domino properties
- Stable placement on surface
- Trigger mechanism
- Environmental considerations
Chain Reaction Design
- Test reliability of toppling
- Account for bounce and scatter
- Use guides or channels
- Multiple parallel chains
- Branching and merging paths
Advanced Domino Effects
- Spirals - Curved domino paths
- Stairs - Multi-level chains
- Splits - One domino triggers multiple
- Delays - Slow sections
- Jumps - Gaps in chain
Confined Stacking
Container Physics
Stacking within boundaries:
- Wall friction affects settling
- Pressure distribution
- Particle packing behavior
- Flow and avalanche effects
- Stable vs. chaotic packing
Piling Dynamics
Objects falling into container:
- Drop height affects energy
- Order affects final configuration
- Shape affects packing density
- Mass affects pressure
- Friction affects angle of repose
Best Practices
Creation Process
- Bottom-up - Always build from base
- Settling time - Let physics stabilize
- Incremental - Add pieces gradually
- Positioning - Precise initial placement
- Testing - Verify stability before continuing
Stability Tuning
- Start with high friction (0.5-0.8)
- Use low restitution (0.0-0.1)
- Increase solver iterations for tall stacks
- Enable sleeping for stable stacks
- Test with disturbances
Common Pitfalls
- Creating entire stack at once
- Misaligned centers of mass
- Insufficient friction
- Too few solver iterations
- Sharp corners causing instability
- Excessive initial velocities
Performance Considerations
- Large stacks are expensive
- Use sleeping for stable regions
- Consider static bodies for permanent structures
- Limit active collision pairs
- Profile with target stack size
Gameplay Applications
Building Games
Player-constructed structures:
- Provide stability feedback
- Show center of mass
- Highlight unstable connections
- Undo/redo for iteration
- Save/load structures
Destruction Games
Knocking down structures:
- Score based on destruction
- Chain reactions increase score
- Precision vs. power tradeoffs
- Multiple attempt strategies
- Progressive difficulty
Puzzle Games
Stability as puzzle mechanic:
- Required formations
- Limited pieces
- Precise placement challenges
- Physics-based solutions
- Time or move limits
Advanced Techniques
Active Stabilization
Helping unstable stacks:
- Temporary constraints
- Gradual activation
- Damping during creation
- Collision filtering during build
- Motor drives for correction
Procedural Stacking
Automated structure creation:
- Algorithmic placement
- Stability testing
- Iterative adjustment
- Random variations
- Validated generation
Destruction Analysis
Studying collapse:
- Identify failure points
- Force distribution
- Progressive collapse
- Energy dissipation
- Debris patterns
Testing and Validation
Stability Tests
- Apply small impulses
- Test with time acceleration
- Environmental disturbances
- Collision from projectiles
- Sustained loads
Stress Testing
- Maximum stack height
- Overloading structures
- Worst-case configurations
- Edge case geometries
- Performance under load
Related Skills
When users need information about:
- Material properties - Use unity-physicscore2d-materials
- Collision behavior - Use unity-physicscore2d-collision
- Shape optimization - Use unity-physicscore2d-shapes-advanced
- Physics settings - Use unity-physicscore2d-settings (if available)
- Performance - Use unity-physicscore2d-performance
Worked Examples
All examples below assume the standard PhysicsCore2D OnEnable/OnDisable lifecycle. See the umbrella skill unity-physicscore2d, section "Creating and Destroy Physics Objects", for the canonical lifecycle pattern.
- examples/Arch.cs — stone arch built from trapezoidal voussoirs + keystone + 4 box weights; friction-sensitive structural stack.
- examples/CardHouse.cs — 5-story card house using extremely thin rectangles balanced at angles; stress test for stable thin-shape stacking.
- examples/DominoChain.cs — five domino shelves (alternating tip directions) triggered by a small
ApplyLinearImpulse to the first/last domino of each row.
- examples/Pyramid.cs — large pyramid stack of dynamic boxes (default 1830 bodies); slight corner radius for stacking stability + chamber walls catch any collapse.
