Particle System 4: Force Control Modules
Apply physics forces to particles using the Force over Lifetime module and Unity's Particle System Force Fields.
Overview
The Force over Lifetime module and Force Fields give you physics-based control over particle movement — attractors, vortexes, turbulence, and custom force volumes.
Force over Lifetime
Applies a constant or animated acceleration to every particle. Unlike Velocity over Lifetime (which sets speed directly), Force over Lifetime changes speed gradually — simulating real forces.
Settings
- X, Y, Z — Force vector components. Can be constant, random, or animated curves.
- Space — Local or World (same as Velocity module)
- Randomize — Adds random variation each frame for more organic-looking motion
Common uses
| Force | Application |
|---|---|
| Negative Y | Custom gravity (more artistic than the global gravity modifier) |
| Positive Y | Buoyancy — bubbles, helium balloons |
| Oscillating X/Z | Wind turbulence on leaves/snow |
Particle System Force Fields
Force Fields are scene objects that influence particles from any Particle System configured to use them. This lets you create global attractors and repulsors.
Adding a Force Field
- Create an empty GameObject → Add Component → Particle System Force Field
- In your Particle System, enable External Forces module
- Set Influence Filter to specify which force fields affect this system
Force Field types
- Sphere — Radial force (attract or repel) based on distance from center
- Hemisphere — One-sided radial force
- Cylinder — Force along a cylindrical axis (good for vortex effects)
- Box — Uniform force inside a volume
Force Field parameters
- Start/End Range — Inner and outer radius of influence
- Gravity — Attraction (negative) or repulsion (positive) strength
- Rotation Speed — Spins particles around the force field center (vortex!)
- Drag — Slows particles inside the field
- Vector Field — Use a texture to define arbitrary 3D flow patterns
Example: Magic vortex
- Create a Cylinder Force Field, Gravity = -2, Rotation Speed = 45°/s
- Point your particle system’s Cone emitter at the force field
- Particles will spiral inward — great for portals, black holes, drain effects
Tips
- Use Force over Lifetime for global, uniform forces on all particles
- Use Force Fields for spatially-localized, scene-based forces
- Combine both: global gravity (Force over Lifetime) + local attractor (Force Field) for complex effects
Next steps
In Lesson 5 we’ll look at importing and using pre-built Particle System packages from the Unity Asset Store.