The Physics Time Factor parameter enables full control over physical time. The particles can be made to move faster, slow down, completely freeze or move backwards. And all this while the camera is fully controllable so it can move around in the scene. To freeze time, the Physics Time Factor parameter has to be keyframed down to 0. If it is simply set to zero, no particles will ever be born.
Step-by-step instructions on using Physics Time Factor to Freeze time
Create a new comp (Ctrl/Cmd-N), make it 640*480 at 30 fps. 5 seconds long. Name it "Main".
Create a new comp-sized solid (Ctrl/Cmd-Y), name it "Particles". Make sure to click "Make Comp Size" before OK.
Apply Effect>Trapcode>Particular to the solid.
To be able to navigate easily in the scene, create a compostion camera:
Select Layer>New>Camera and use the 28mm preset.
First, let's keyframe the camera:
Go to time 2:00 (2 seconds) and set a keyframe for Position (the default: 320,240,-499).
Go to time 3:00 (3 seconds) and set a keyframe for Position: 0,240,-380.
Try a RAM preview:
Now let's use Physics>Physics Time Factor to slow things down during the camera move:
Go to time 1:00 (1 seconds) and set a keyframe with value 1.
Go to time 1:20 (1 seconds and 20 frames) and set a keyframe value 0.
Go to time 3:10 (3 seconds and 10 frames) and set a keyframe value 0.
Go to time 4:00 (4 seconds) and set a keyframe with value 1.
Try a RAM preview:
