Physics group> Air group> Motion Path

The Motion Path feature makes it possible to precisely control the path that a particle takes after being emitted. This is done by setting keyframes for a comp Light in After Effects and naming the Light to start with the name "Motion Path" followed by a number between 1 and 9. This keyframed Light lets you control the path that particles travel after being born. Motion Path is useful when precise control of the particle path is needed. Read our tutorial 'Setting up a Motion Path' at the bottom of this page.

An example of motion path with a keyframed Light.

The Motion Path menu showing the first and second group of nine options.

The number values

The menu for Motion Path is the only Particular control that you will set when creating a motion path. Each of the numbers corresponds to a number 'X' defined in the name of the light. That number is used in the name given to the comp Light that acts as the position source.

HQ or not HQ?

In the Motion Path menu, you will notice there is an 'HQ' (High Quality) variant of each number. If the Motion Path Light moves extremely quickly, the particle position will not be calculated accurately using the standard setting. The Light's path should have a smooth interpolated curve, so if you notice that the particles are not following the path of the light closely enough then select the HQ variant instead. A word of warning: The HQ setting is much slower, so do not use it unless a smooth interpolation is required.

Tutorial: Setting up a Motion Path
Create a new comp (Ctrl/Cmd-N). Set the composition to be 640x480, with a frame rate of 30 and length of 5 seconds. Name it 'Main'. Create a new comp-sized Solid (Ctrl/Cmd-Y). Name it 'Particles', click the Make Comp Size button, and click OK. Apply Effect > Trapcode > Particular to the Solid.

To use the Motion Path feature, first create a comp Light (Layer>New>Light). This should be a Point or Spot Light. The other Light settings (like Color and Intensity) do not matter.

The name of the Light has to be 'Motion Path X', where X is a number between 1 and 9. Let's use 1 in this example.

The Light Settings dialog showing the proper name for a light that will serve as a motion path source for Particular.

Make sure the Light's position is where you want particles to be born. Also make sure the Emitter > Position, where particles are born, corresponds to the position of the light on the first frame of the layer. Then turn off Emitter> Velocity by setting the value to 0. This will keep the particles from spreading out over time. Set Particle > Life high enough so the particles live for awhile and don't die mid-path.
Set Physics > Air > Motion Path to 1. (Or if you used another value for X, use that instead)

The Motion Path menu option correctly set to "1".

The keyframes for the Light object named Motion Path 1 in the Timeline.

Select the Light layer in the Timeline and hit 'P' to reveal the Position property. Now simply set some keyframes for the Light's Position property and the particles will follow! (Make sure you are keyframing the Light's position, not the position of the layer that is generating the particles.)

The default particles and Light in the composition.

The particles appear in the center after the Velocity is set to 0.

Keyframes are drawn for the light and the particles follow the path of the keyframed light in 3D space. (In this case, the emitter position is offset from the initial position of the light so you can see the path and the particular result at the same time.)