Giving Objects Some Jiggle and Bounce

Have you ever sat and watched what happens when a beach ball gets hit or bounces off of the ground? Or seen what happens when someone places a plate of gelatin on a table? Or observed how a person's hair moves when they shake their head? When these things move and collide with other objects, they have a bit of internal jiggle that can be difficult to reproduce correctly with regular animation tools. This jiggling is the basis for what is referred to as soft body dynamics.

You can simulate soft body dynamics in Blender from Physics Properties. Left-click the Soft Body button, and a Soft Body panel appears. In that panel, you can make adjustments and tweak the behavior of your soft body simulation.

What follows is a simple step-by-step process for creating a simple soft body simulation with the default cube object:

1. Select the cube with a right-click and grab it up in the Z-axis so that it floats above the 3D grid (GZ).

   You want to give the cube some height to fall from. It doesn't have to be very high; 3 to 5 units should be enough.

2. Create a Plane mesh as a ground plane (Shift+AMeshPlane) and scale it larger so that you have something for the cube to hit (S).

   This plane is the surface for your jiggly cube to bounce off of. It may be helpful to put your 3D cursor at the origin (Shift+SCursor to Center) before adding the plane.

3. Add a Collision panel in Physics Properties to give your plane collision properties.

   Doing so makes Blender understand that the plane is an obstacle for your falling cube.

4. Right-click the cube to select it.
5. Make a Soft Body panel in Physics Properties.

   That's all you really have to do to enable soft body physics on your 3D objects. However, in order to get the cube to properly act according to gravity, there's one more step. Notice that adding soft body properties to your cube reveals a bunch of new panels to Physics Properties.

6. Disable the Soft Body Goal check box next to its panel.

   This step disables the default goal behavior of soft bodies. When Soft Body Goal is enabled, you can define a group of vertices in the object to be unaffected by the soft body simulation. A scenario where you may want to have Soft Body Goal enabled would be a character with loose skin, like the jowls of a large dog. You may want the dog's snout to be completely controlled by your armature animation, but have the jowls that hang off to be influenced by soft body simulation. Because in this case with the cube you want the entire object to be affected by the simulation, it's best just to turn it off.

7. Play back the animation (Alt+A) to watch the cube fall, hit the ground plane, and jiggle as it lands again.

   Pretty cool, huh? Figure 13-6 shows this process being completed. As with particles, it's a good practice to make sure that you're at the start frame of your animation before playing back your simulation.

Figure 13-6: Dropping a jiggly cube into the scene.

Now, I have to admit that I cheated a bit in the preceding example by using a cube. If you were to try those steps with another type of mesh, like a UV Sphere or Suzanne, the mesh would collapse and look like it instantly deflated when it hit the ground plane. In order to get around this issue, you need to adjust one more setting. In the Soft Body Edges panel on the left column of values is a setting labeled Bending with a default value of 0.00. This value sets the bending stiffness of your object. With a setting of zero, you have no stiffness, so the mesh collapses. However, if you change this setting to a higher value, such as 3.0 or 5.0, the falling mesh retains its shape a little bit better when it collides with the ground plane. You can also enable the Stiff Quads check box in this panel to get your mesh to retain its shape even better, but be careful: This setting slows down the soft body calculation substantially.