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When it comes to creating dynamic simulations, there are two object types that you'll probably hear mentioned on a regular basis: rigid bodies and soft bodies. These labels, or descriptions, refer to the type of objects that a particular simulation has been designed to work with, or, more accurately, to re-create. The term rigid bodies refers to the simulation of solid unyielding objects whose subcomponents--that is, vertices, faces, and edges of the object--do not deform in any way during the course of the simulation.
Now, in the real world very few such objects exist. Crash a large solid truck into a solid brick wall and even at relatively low speeds, some parts of both objects will deform, probably even break. However, in order to create a predictable and repeatable simulation environment, such effects are not allowed to occur inside a rigid body simulation. If we wanted to see rigid body dynamics at work, all we would need to do would be to look at pretty much any action- adventure film, game, or TV show these days and we would probably see an example of rigid body dynamics at work.
One often-seen use is the destruction and collapse of solid objects such as buildings and walls. These objects are first broken, or fractured, into multiple pieces and then their motion is simulated using rigid body dynamics. Artists can, just as easily though, use rigid body simulation tools for much less spectacular but equally important production tasks such as setting up otherwise time-consuming aspects of a 3D scene: a jar full of coins or sweets, a toy chest full of cars or spaceships, an alleyway strewn with debris and litter.
These are processes that could take considerable time to work through manually, but that can be handled very easily with rigid body simulation tools. Soft body objects, by contrast, behave in a very different manner--very different that is as compared to their rigid body counterparts. In a soft body simulation, the shape of an object is actually required to change over time. This can be accomplished because the relative distance of any two points on a soft body object are not considered to be fixed as they are in a rigid body simulation. While it's deforming though, a soft body object is usually expected to retain its general shape and volume to some degree, so as to keep it recognizable to the viewer.
Now, the scope of, or uses of, our soft body dynamics, again, really is quite broad-ranging. This could be the simulation of soft organic materials, and here we might think of muscle and fat, even hair and vegetation, to other parts more obvious deformable object types, such as clothing and fabric in general. Which of these simulation types--that is, rigid body or soft body--we choose to work with will naturally depend entirely upon the type of object and the motion that we are trying to emulate. The good news with the MassFX system in 3ds Max is that we can use both rigid and soft body objects inside the same simulation, even having them interact very nicely indeed with one another.
One thing we do need to keep in mind as we produce our simulations though, is that, typically speaking, the idea behind tool such as MassFX is to provide a visually plausible emulation rather than a super-accurate scientific or engineering simulation. In our next video, we will look a little more closely at rigid body objects and consider three rigid body types that are available to work with inside our simulations.
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