You can add surface interactions and collisions to 
		Paint Effects strokes by setting 
		Tubes attributes 
		Surface Snap, 
		Surface Collide, and 
		Surface Attract. These options are described in the following sections of 
		Paint Effects Brush Settings: 
	 
To add surface interaction and collisions to 
		Paint Effects strokes 
- 
Shift-select the Paint Effects 
		  stroke and collision geometry. 
		
- Select 
		  . 
		  The stroke and selected geometry can now collide. 
		   
- Select the 
		  Paint Effects stroke; in the 
		  Attribute Editor for the brush, open the 
		   attributes and turn on 
		  Surface Snap. 
		  
 
		  The start position of each tube now snaps to the closest points on the surface of the collision geometry. 
			  
- Open the 
		   section, where you can experiment with the following settings to control the interaction between the stroke and the object: 
		  
- If some strokes interpenetrate the geometry, and you want to prevent this, turn on 
				Surface Collide. 
				
			 
- Set 
				Collide Method to specify whether the stroke should collide with the 
				Outside, 
				Inside, or 
				Both Sides of the object surface. 
			 
- Increase 
				Surface Attract to apply a force that pulls tube end points back toward the geometry surface. 
			 
- Set 
				Max Attract Distance to specify the area affected by the attractive force. 
				
			 
- Increase 
				Gravity to apply a force that pulls tubes downward.
			 
To better understand the effects of other 
			 Forces settings such as 
			 Random and 
			 Uniform Force, see 
			 Forces brush settings.