You can optionally enter the speed that should be converted to a velocity.
This value is the speed measured in units per second.
This normal sets the direction of the velocity. For example, a value of (0;0;1) will cause the particles to move in the direction of their Zaxes. However, since this node is not directly connected to a particle stream, you can use it to calculate velocity for any purpose, not just to set the velocity of the particles.
Outputs the velocity, as a vector, computed from the Speed and Axis values. If you want this value to control the velocity of particles, connect the port to the Velocity input port of a PSetData node.