Physics group> Air group

Air is one of two Physics Models offered in the Physics group. The Air model can change particles to make them appear to move naturally through air with resistance, spin, turbulence and more. This group of controls contains Air Resistance, Wind direction, and other settings. Air contains two displacement systems called Turbulence and Spherical. There is also a control called Motion Path which offers path-based movement for the particles.

Technical note: In explaining the Air controls, we will often refer to the 'spin' of a particle. By this, we mean the circular, spring-like, random motion of particles. There is no 'Spin' setting, but there are many controls that affect this spinning motion.

At left, the full Air group. At right, the Air option in Physics Model.

Motion Path

Motion Path is a set of menu options that lets you make the particles follow a user-defined 3D path. The path is defined relative to the 'normal' path that particles would take if this setting was not used. Therefore it is important to move the Emitter to where the path actually starts. Read about how to use Motion Path.

The Motion Path popup lets you choose a mask as a path that the motion will follow.

This is an example of particle trail along a motion path.

Air Resistance

Air Resistance makes the particle velocity decrease over time as the particle's move through space. Useful for explosions and fireworks where particles should start with a high velocity and then gradually slow down. Velocity is set with the Emitter > Velocity control.

Air Resistance Off |  | Air Resistance On

Air Resistance Rotation (new in version 2.0)

Air Resistance stops the particles' flight by decreasing their velocity, then Gravity takes over and particles start to fall. But as the particles stop flying, they should also not rotate. There's a new setting that takes care of this.

If Air Resistance Rotation is check marked, Air Resistance will also affect the rotation of particles. The particles will rotate fast in the beginning, but as they get slowed by Air Resistance, their rotation will decrease. This behavior helps to make the movement look natural. Particle rotation is set with the Particle group> Rotation group. Remember that full 3D rotation applies only to Textured Polygon particle types.

Spin Amplitude

Spin Amplitude makes particles move in randomized, circular orbits. A value of 0 turns off the spinning motion. Low values make small circular orbits. High values make large circular orbits. This behavior is useful for adding randomness to particle motion, which makes the animation look more natural. Amplitude can also be used to create a swarming look to the particles. Apply the t2_OrangicLinesMotion to see the spin control in action.

Spin Frequency

Spin Frequency sets how fast the spinning particles move in their orbit. Low values mean the particles spin slowly in their orbit. Higher values make the particles spin faster. The clips below were rendered with Motion Blur to show the motion clearly.

Amplitude off, no spin motion |  | Frequency low, Amplitude 100 |  | Frequency high, Amplitude 100

Fade-in Spin [sec]

Fade-in Spin sets how long the particle lives before it is fully affected by the spin. Measured in seconds. High values means the spin takes awhile before the spin affects the particles, making the animation fade in gradually overtime.

Version 1.5 Note: Fade-in Spin was previously called Time Before Spin.

Wind X, Y, Z

The Wind controls makes all particles move uniformly in the Wind direction. Wind X move the particles left or right, and Wind Y move the particle up or down. Wind Z will make the particles appear to move into or out of the screen. To make the Wind more realistic, Wind can be keyframed so it varies a little over time. Adding some Spin or Turbulence also helps to increase the realism.

Visualize Fields

The Visualize Fields checkbox simplifies working with Turbulence Field or Spherical Field. When working with the Field groups, sometimes you need to know exactly how the displacement field looks. Turn this checkbox On to make all fields viewable. Doing so lets you adjust the field more easily.

Version 1.5 Note: This checkbox was previously called Visualize and used to only affect the Spherical Field.

Turbulence Field

The Physics Air group offers two kinds of displacement models to push along the particles. One is the Turbulence Field. Turbulence is not based on fluid dynamics. Instead, it is a 4D displacement based on Perlin Noise fractal. Turbulence adds motion so the particles that are close to each other get a similar, but not equal, random motion.

This behavior helps tremendously when creating fire and smoke effects to make particle motion look natural. Unlike fluid dynamics, Turbulence computes quickly and does not depend on a simulation that starts at the first frame. Thus the turbulence result can be seen quickly at any point in the simulation. Visit the Turbulence Field group page to get more in-depth information.

Spherical Field

The Physics Air group has another kind of displacement model for particle pushing. This is Spherical Field, a displacement field in the form of a sphere. The sphere can either push particles outward or suck them in. Spherical is not a force field. The effect of the field is instant, and does not leave a trace once the field is removed. You can find more information on the Spherical Field group page.