# What's the meaning of tangent in the velocity panel in the particle settings?

I wish to know the meaning of the "tangent" option available in particles panel; for a surface in 3D, tangent means a surface. But velocity is a linear, directional entity.

I am currently working on a project which involves emission of particles along the slope of a cone.

Strictly, 'tangent' means a vector that touches the surface at precisely one point. Not the surface itself. So in the particle setting context:

tangent controls the starting force that is applied to the particle parallel to the emitter surface.

Normal controls the force that is applied to the particle perpendicular to the emitter surface.

To put it another way,

tangent = 1, normal = 0 will make the particle emit 'sideways'.

tangent = 0, normal = 1 will make the particle emit 'out'.

tangent = 1, normal = 1 will make the particle emit at 45degrees to the surface.

• What if the emitting surface is a plane? All directions are parallel to the surface. In that case what will be the direction of the velocity of the particles emitted, if the tangent value is 1 ? Jun 13, 2013 at 17:40
• Then the direction of the velocity depends on the Rotation value underneath is. Try it out with a simple particle system (best to turn off gravity to see things more clearly) Jun 13, 2013 at 19:54
• I tried that too...for a plane I couldn't observe any rotation at all...when the ROT value was increased above 0.5, then the velocity direction simply became opposite. But I was not able to fix/find the direction of the initial tangential velocity. Jun 14, 2013 at 18:41