unity-physicscore2d-forces - SKILL.md Agent Skill

name: unity-physicscore2d-forces description: Environmental forces (wind), surface forces, and directional force application

Unity PhysicsCore2D Forces Expert

You are now acting as a Unity PhysicsCore2D forces expert, specialized in applying forces, impulses, and environmental effects.

Overview

PhysicsCore2D supports various force application methods:

Impulses - Instantaneous velocity changes
Forces - Continuous acceleration
Torque - Rotational forces
Environmental forces - Wind, gravity fields
Surface forces - Conveyor belts, moving platforms
Explosion forces - Radial force application

Repository Examples

Reference examples from the PhysicsExamples2D repository:

Force Application Methods

Applying Impulses

Instant velocity changes (for impacts and jumps):

Modify linear velocity directly
Apply at body center or specific point
Immediate effect
No accumulation needed

Use cases:

Jumping
Impacts and collisions
Launch mechanics
Knockback effects

Applying Forces

Continuous acceleration over time:

Accumulate during physics step
Applied as acceleration
Cleared after each step
Requires Update or FixedUpdate

Use cases:

Character movement
Vehicle propulsion
Constant acceleration
Continuous push/pull

Applying Torque

Rotational forces:

Changes angular velocity
Applied at body center
Can be impulse or continuous
Affects rotation only

Use cases:

Motor rotation
Spinning objects
Angular momentum
Torque-based control

Point Forces

Forces applied at specific points:

Generate both linear and angular effects
Calculate torque automatically
Offset from center of mass matters
More realistic physics

Environmental Forces

Wind Systems

Global or area-based wind:

Apply force to all dynamic bodies in area
Can vary by height or position
Directional or turbulent
Affects light objects more

Implementation approaches:

Global wind field
Wind zones with boundaries
Particle-based wind
Noise-based turbulence

Gravity Fields

Custom gravity in areas:

Override default gravity
Directional gravity
Radial gravity (planet-like)
Zero gravity zones

Buoyancy

Upward force in fluids:

Based on submerged area
Density-based calculation
Drag and viscosity
Water or other fluids

Magnetic Fields

Attraction or repulsion:

Distance-based force
Affects specific objects
Inverse square law
Directional control

Explosion Forces

Apply radial force from a point:

Calculate direction to each body
Apply force based on distance
Can include upward bias
Add impulse to affected bodies

Implementation:

void ApplyExplosionForce(Vector2 center, float radius, float force)
{
    // Query for bodies in radius
    // For each body:
    //   - Calculate direction from center
    //   - Calculate distance falloff
    //   - Apply impulse based on force and distance
}

Force Zones and Triggers

Force Areas

Trigger zones that apply forces:

Detect bodies in zone
Apply force while inside
Wind tunnels, currents
Damage zones

Directional Zones

Push objects in a direction:

Conveyor belts
Rivers and currents
Accelerator pads
Launch pads

Vortex Forces

Spinning force fields:

Circular force pattern
Pull toward center
Rotational component
Whirlpools, tornadoes

Best Practices

Force vs. Impulse

Use impulses for instant changes (jumps, hits)
Use forces for continuous effects (movement, wind)
Impulses don't need accumulation
Forces scale with time

Force Magnitude

Start with small values and tune
Scale forces by body mass if needed
Consider physics timestep
Test with different object sizes

Performance

Minimize number of force queries per frame
Cache force zone results
Use spatial partitioning for large areas
Only calculate forces for active bodies

Stability

Very large forces can cause instability
Limit maximum velocity if needed
Use damping to prevent runaway motion
Clamp force magnitudes

Realism

Apply forces at correct points
Consider mass and drag
Add appropriate resistance
Balance force strength

Advanced Techniques

Turbulence

Add randomness to forces:

Perlin or Simplex noise
Time-varying direction
Position-based variation
Realistic wind effects

Force Fields

Custom force field shapes:

Grid-based force lookup
Texture-based force maps
Procedural fields
Baked force data

Drag Forces

Resistance based on velocity:

Linear drag (low speed)
Quadratic drag (high speed)
Angular drag
Fluid resistance

Related Skills

When users need information about:

Velocity control - Use unity-physicscore2d (main skill)
Material properties - Use unity-physicscore2d-materials
Query for bodies in area - Use unity-physicscore2d-queries
Trigger areas - Use unity-physicscore2d-filtering

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/ApplyForceBasics.cs — minimal demo of ApplyForceToCenter, ApplyLinearImpulseToCenter, ApplyTorque, and ApplyForce (at offset point) on a single dynamic body, mapped to arrow keys + space.
examples/Wind.cs — vertical chain of dynamic bodies on spring hinges; PreSimulate event applies PhysicsShape.ApplyWind(wind, drag, lift) per shape with low-pass-filtered noise.
examples/Explosion.cs — PhysicsWorld.Explode(ExplosionDefinition) invoked on Space key; impulse scales by impulsePerLength over each body's perimeter inside the blast radius.