Physics group> Physics Bounce

Bounce is one of two Physics Models used by the Physics group. The Bounce model is used to make particles bounce off of specific layers in the composition.

Two layers can be specified: the Floor and the Wall. The Floor and Wall layer must stand still: they cannot contain any keyframes. The camera can move around in the scene, but the Floor and Wall must be fixed in the scene: otherwise Particular cannot calculate the correct position for the particle motion.

Read a tutorial on Bouncing Particles on Layers.

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

Floor Layer

Use this menu to select a Floor Layer for the Bounce. The Floor layer should be a layer with the 3D layer switch enabled. The Floor must have the 'Continuous Rasterize' layer switch turned off. The Floor cannot be a text layer, but you can use text in a pre-comp.
When the Floor Layer is selected, a control light named 'Floor [layername]' is created. This is a locked, shy layer and should not be edited. It is just there to help Trapcode Particular keep track of the Floor position.

The Floor Layer menu shows available layers from the composition.

Floor Mode

Use the Floor Mode to select either the Infinite Plane, Layer Size or the Layer Alpha options.

The Floor Mode options menu.

Particular can use three different modes to calculate the size or extents of the floor:

- The Infinite Plane option extends the dimension of the layer to an infinite size and particles will not bounce around or off of the edge of the layer.
- The Layer Size option simply uses the layer's dimension to calculate the bounce area.
- The Layer Alpha option will use the area defined by the layer's alpha channel to calculate the bounce area. Use this option to create an area inside the layer's extent for the bounce area. For example, you could define a circular mask for a layer, and the mask (which sets the alpha values for the layer) will define the bounce area.

Wall Layer

Use this pop-up to select a Wall Layer for the Bounce. The Wall layer should be a layer with the 3D layer switch enabled. The Wall must have the 'Continuous Rasterize' layer switch turned off. The Wall cannot be a text layer, but you can use text in a pre-comp.
When the wall layer is selected a control light named 'Wall [layername]' is created. This is a locked, shy layer and should not be edited. It is just there to help Trapcode Particular keep track of the Wall position.

The Wall Layer menu shows available layers from the composition.

Wall Mode

Use Wall Mode to select either the Infinite Plane, Layer Size or Layer Alpha options.

The Wall Mode options menu.

Particular offers the same available options for the Wall Mode as the Floor mode above.

Collision Event

Controls what happens during a collision with options to allow the particles to bounce, slide, stick, or kill.

The Collision Event options menu.

- The Bounce collision mode is the default, and will cause particles to bounce off the layers defined in the floor and wall menus, just as a ball would bounce off of the floor in the real world. Only in this mode can you set the Bounce, Bounce Random, and Slide controls (explained below).
- The Slide option causes the particles to only slide parallel to the floor or wall after the collision. This is useful for emulating a thick liquid such as oil pouring into a Teflon pan. The result is the liquid sliding round on the surface, not bouncing away from it.
- The Stick mode makes the particles stop and remain exactly where they collide with the bounce layers. This useful for creating an effect such as snow building up on an object.
- The Kill mode removes the main particle when it contacts the bounce layers. This is useful when the Aux Emitter control Emit is set to Emit at Collision. You can use the main particle type to create one appearance and the aux system to create a secondary type of particle with a different appearance after the bounce event.

Bounce

The Bounce control determines how much energy is conserved during the Bounce. High values make the particles bounce higher after the collision while low values cause the particles to bounce very little, losing most of their momentum from the collision.

Bounce Random

This control sets the randomness for the Bounce value. High values apply more randomness to the Bounce. Bounce Random makes the particles bounce a little differently in height. This can make the result look more realistic, since objects that strike a surface in the real world don't all have the same momentum or post-collision velocity.

Slide

The Slide control sets the momentum of the the particles parallel to the surface. High values mean the particles will slide off the surface quickly, like objects hitting ice. Low values mean particles will stall or stick to the surface. If the Bounce and Slide control are set to a value of zero, the result will be the same as setting the Collision Event to Stick mode instead of Bounce.