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Understanding volume, mass, and density

From: Creating Simulations in MassFX and 3ds Max

Video: Understanding volume, mass, and density

If you've ever spent any time working with a photographic camera--be that film or digital--set in manual mode, you will probably become aware of the exposure triangle-- that is, the shutter speed, ISO, or film speed, and F-stop or F number values. These three settings are all interdependent, and any one of them can be used to alter the exposure, or level of light captured in a photograph. In fact, if you've spent any time lighting and rendering inside a 3D application or render engine that uses a physical camera model, you will also have encountered this triangle.

Understanding volume, mass, and density

If you've ever spent any time working with a photographic camera--be that film or digital--set in manual mode, you will probably become aware of the exposure triangle-- that is, the shutter speed, ISO, or film speed, and F-stop or F number values. These three settings are all interdependent, and any one of them can be used to alter the exposure, or level of light captured in a photograph. In fact, if you've spent any time lighting and rendering inside a 3D application or render engine that uses a physical camera model, you will also have encountered this triangle.

Now, we mention this because when it comes to creating believable dynamic simulations, we do come across a very similar triangle system, one that affects how objects will behave inside the simulation. These are the volume, mass, and density parameters of an object. These three measurements are interdependent, and so a change to any one of them will affect the makeup of the other two. They are all used by a physics simulation engine to determine how an object ought to behave whilst it is both at rest and in motion.

Now, the volume of an object is already known to your 3D application. It is based upon its size, or the amount of space that it occupies inside the 3D environment. If we want an object's volume to be accurately calculated in a MassFX simulation, we must create or model our geometry at real-world scale. This really is vital if we want realistic behavior from our simulated objects. Mass is a measurement that is often confused with weight, but the two are not, strictly speaking, the same thing, although it is true that here on Earth greater mass does oftentimes equate to a heavier object.

Mass is, in reality, a measurement of the amount of matter making up an object. This of course never changes, regardless of the environment that an object is placed in. So for example, an object with a mass of 1500 kg here on the earth still has a mass of 1500 kg if it is placed on the moon. The amount of matter making up the object never alters. Of course the change in environmental gravity will mean that the object would weigh less on the moon as weight is really a measurement of gravity at work on an object in a specific location.

In order for the simulator to know how much mass our objects have, we generally need to supply that information in a setting of either grams or kilograms. In MassFX, the Mass parameter is set using kilograms. Density is a measurement of an object's mass based on the volume or area of three-dimensional space that it is packed into. The greater the mass packed into a fixed volume, the denser a material is said to be. Now, this could also be expressed as, the smaller the volume a fixed mass is packed into, the denser the material is set to be.

Once our software knows the volume and mass of an object, it can automatically determine the correct density, as this is calculated through the formula of mass divided by volume. Naturally, once you have all of that information correctly piped into our system, our objects are going to stand a much better chance of behaving in a realistic manner when they're simulated. Now, whilst it is vital to understand both the environmental--such as gravity and drag--and object-specific properties-- such as volume, mass, and density that affect our simulations--they are naturally all the elements that we need to have an understanding of, if we're going to be able to fine-tune our simulations and make them thoroughly believable to our audiences.

These come in the form of Newton's three basic laws of motion, which we will be taking a brief look at in our next video.

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This video is part of

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Creating Simulations in MassFX and 3ds Max

51 video lessons · 2432 viewers

Brian Bradley
Author

 
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  1. 3m 27s
    1. Welcome
      58s
    2. Working with the exercise files
      46s
    3. Setting up the 3ds Max project structure
      1m 43s
  2. 39m 20s
    1. Why simulate and not animate?
      3m 38s
    2. A look at gravity and drag
      3m 55s
    3. Understanding volume, mass, and density
      3m 45s
    4. What are Newton's laws of motion?
      3m 20s
    5. Finding believable frames per second and substeps
      3m 5s
    6. Understanding the difference between rigid and soft bodies
      3m 28s
    7. More about rigid body types
      3m 32s
    8. How collisions are calculated
      4m 35s
    9. Learning the difference between concave and convex meshes
      6m 24s
    10. What is a constraint and how do we use it?
      3m 38s
  3. 24m 20s
    1. A look at the MassFX and the 3ds Max user interfaces
      5m 52s
    2. Exploring the MassFX workflow
      5m 14s
    3. Discovering ground collision and gravity
      4m 49s
    4. Adjusting substeps and solver iterations
      3m 43s
    5. Using the Multi-Editor and the MassFX Visualizer
      4m 42s
  4. 44m 11s
    1. Breaking down the shot
      4m 51s
    2. Setting up the launchers
      3m 59s
    3. Setting up the drop system
      4m 30s
    4. Prepping the cans
      3m 33s
    5. Refining the simulation on the launchers
      5m 9s
    6. Refining the simulation on the colliders
      6m 5s
    7. Baking out the simulation for rendering
      5m 37s
    8. Reviewing the simulation with an animation sequence
      5m 3s
    9. Adding an animation override
      5m 24s
  5. 33m 32s
    1. Adding a rigid constraint and creating breakability
      8m 3s
    2. Creating a moving target with the Slide constraint
      4m 47s
    3. Creating springy targets with the Hinge constraint
      5m 59s
    4. Spinning targets using the Twist constraint
      4m 57s
    5. Creating crazy targets with the Ball & Socket constraint
      4m 58s
    6. Constructing a MassFX Ragdoll
      4m 48s
  6. 36m 51s
    1. Applying the mCloth modifier and pinning the hammock
      5m 55s
    2. Setting up the hammock's physical properties
      5m 39s
    3. Working with the mCloth interaction controls
      6m 14s
    4. Attaching the hammock to animated objects
      4m 5s
    5. Putting a rip in mCloth
      6m 14s
    6. Using mCloth to create a rope object
      4m 53s
    7. Creating a soft body object
      3m 51s
  7. 14m 47s
    1. Adding forces to a simulation
      5m 27s
    2. Putting forces to practical use
      5m 33s
    3. Using forces with mCloth
      3m 47s
  8. 35m 27s
    1. Walking through mParticles
      4m 38s
    2. Using fracture geometry
      6m 0s
    3. Creating breakable glue: Part 1
      4m 19s
    4. Creating breakable glue: Part 2
      5m 19s
    5. Creating a gloopy fluid: Part 1
      4m 14s
    6. Creating a gloopy fluid: Part 2
      4m 41s
    7. Adding forces to mParticles
      6m 16s
  9. 1m 5s
    1. What's next?
      1m 5s

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