Rigid Body Dynamics: Creating Hard Effects

Rigid body dynamics are used to show how motion occurs with rigid bodies. These dynamics take inertia, mass and other motion dynamics. These rigid bodies cannot be used to deform bodies. These rigid bodies can be used to create hard effects in animation and modeling software. The algorithms used in these create very realistic hard objects and surfaces. In real life, these rigid bodies react differently from other types of objects.


How rigid bodies react when they collide is very different. When rigid bodies collide, they can break, shatter and damage the other object. This is a very different affect from soft bodies. Most of the time multiple collisions will occur. Rock slides, sand and building demolition will use these rigid dynamics. In particular, the different rigid bodies are used for the hardness of objects. There are specific rigid bodies for rocks and so on.

Converting Objects

Unlike most other animations, rigid bodies do not use key frames. Any object can be converted into a rigid body and all different types of fields can influence those rigid bodies. An impulse, velocity and position can all be set and then played back for the motion simulation. The rigid body dynamic engine will constantly calculate motion so that each hard body moves realistically based on your rigid body settings. Key frames make it difficult for the animation to be realist, which is why video animation software uses different engines for rigid bodies.


There are two different types of rigid bodies: passive bodies and active bodies. Active bodies can be moved and are affected by different fields. They can be moved in collisions. Passive bodies cannot be moved and are stationary items. These passive bodies are walls, floors and other objects that are fixed into place. Active bodies can be changed into passive bodies. An example of a rigid body is a bouncing ball or coin that is thrown in the air.


Many times, adjustments will be needed in order to create realistic motion. Play back the new animation and then either keep the default settings or adjust the many different settings. Some of the settings that can be altered include the initial velocity, center of mass, initial spin, impulse, spin impulse, impulse position,mass, static friction, damping, dynamic friction, collision layer, stand in, particle collision, bounciness and more. Each of these adjustments can be made on the x plane, y plane or z plane. Play around with these attributes as different motions will need different settings. Be aware that the playback speeds may be different from seeing the animation in real time.

Complex Objects

Rigid body dynamics will be slightly different for complex rigid bodies such as buildings. Each section of the building will have different nodes attached. This enables each section to react independently. Then, when they are put into sequence, each part of the building sections will be able to react with each other. Each of the nodes will be connected. Many times, the main issue with a building falling is making each piece feel that it has weight. This will require the mass setting to change and rotation to be added to each piece.