### Physics Group > Physics Model Fluid

Fluid is one of three Physics Models used by the Physics group. The Fluid model is used to make particles move in a pattern similar to liquid.

If you're looking to add additional fluid emitters, performance will be much faster if you work within one instance of Particular. Adding fluid emitters on separate Particular instances on separate layers will increase render times dramatically.

Fluid Force

Defines what type of force is applied to the liquid particles

• Buoyancy & Swirl Only: Particles receive an upward or downward buoyant force, as well as a swirling force applied around the entirety of its axis.
• Vortex Ring: Particles receive an upward or downward buoyant force, which is centered in a ring comprised of vortex forces.
• Vortex Tube: Particles receive an upward or downward buoyant force, which is centered by a single vortex force.

From left to right: Buoyancy & Swirl Only, Vortex Ring, Vortex Tube

Apply Force pop up

Determines if the force dictated above is applied Continuously, or only once (At Start) of the effect.

Force Relative Position

A set of X, Y, Z coordinates which determine where in relation to the emitter the forces defined above are applied to the particles.

Force Region Size

Determines the region around the emitter in which the force affects the particle's positions.

Buoyancy

Defines how much upward (positive) or downward (negative) force is applied to the particles.

Random Swirl X, Y, Z

This controls how turbulent swirling forces are applied along the X, Y, and Z axis of the particles. The higher the number, the stronger the forces and the further the particles travel from their original position.

Swirl Scale

Adjusts size of the forces used to create swirl effects; low values produce large swirls, while higher values create smaller swirls.

Random Seed

Adjusts the integer used to create a random effect. Changing this will help give one fluid particle system a slight variation from any others sharing the same parameters.

Vortex Strength

Controls how fast the vortex is spinning, which increases and decreases the strength of its force on the fluid particles.

Vortex Core Size

Adjusts the diameter of the vortex forces used to spin the fluid particles.

Vortex Tilt

Tilts the vortex forces along the axis of the buoyancy force.

Vortex Rotate

Rotates the vortex forces around the axis the buoyancy force.

Note that this will only have a noticeable affect when the vortex tilt has been adjusted.

Visualize Relative Density

Control particle appearance with relation to the combined density of the particles and the fluid forces surrounding them:

• Off: The default setting. Particle appearance is not affected.
• Opacity: Changing the amount of surrounding particles or the strength of fluid forces around it will affect a particle’s opacity. Increased levels make a particle more opaque, decreased levels make it more transparent.
• Brightness: Changing the amount of surrounding particles or the strength of fluid forces around it will affect a particle’s brightness. Increased levels make a particle brighter, decreased levels make it more darker.

From left to right: Visualize Relative Density Off, Opacity, and Brightness.