Updated tutorial_particles_2d (markdown)

tutorial_particles_2d.md

@@ -40,3 +40,40 @@ This parameter is useful because, by rotating the node, gravity will also be rot
 Spread is the angle at which particles will randomly be emitted. Increasing the spread will increase the angle. A spread of 180 will emit in all directions.
 
 <p align="center"><img src="images/paranim3.gif"></p>
+
+#### Linear Velocity 
+
+Linear Velocity is the speed at which particles will be emitted (in pixels/sec). Speed might later be modified by gravity or other acceleations (as described further below).
+
+<p align="center"><img src="images/paranim4.gif"></p>
+
+
+#### Spin Velocity
+
+Spin Velocity is the speed at which particles turn around their center (in degrees/sec). 
+
+<p align="center"><img src="images/paranim5.gif"></p>
+
+#### Orbit Velocity
+
+Orbit Velocity is used to make particles turn around their center.
+
+<p align="center"><img src="images/paranim6.gif"></p>
+
+#### Gravity Direction & Strength
+
+Gravity can be modified as in direction and strength. Gravity affects every particle currently alive.
+
+<p align="center"><img src="images/paranim7.gif"></p>
+
+#### Radial Acceleration
+
+If this acceleration is positive, particles are accelerated away from the center. If negative, they are absorbed towards it.
+
+<p align="center"><img src="images/paranim8.gif"></p>
+
+#### Tangential Acceleration
+
+This acceleration will use the tangent vector to the center. Combined with Radial Acceleration can do nice effects.
+
+<p align="center"><img src="images/paranim9.gif"></p>