unity-physicscore2d-forces

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:

• Wind - https://github.com/Unity-Technologies/PhysicsExamples2D/blob/master/Sandbox/Assets/Examples/Wind.cs
• ConveyorBelt - https://github.com/Unity-Technologies/PhysicsExamples2D/blob/master/Sandbox/Assets/Examples/ConveyorBelt.cs

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:

1. Global wind field
2. Wind zones with boundaries
3. Particle-based wind
4. 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.