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A look at gravity and drag

From: Creating Simulations in MassFX and 3ds Max

Video: A look at gravity and drag

As a technical artist, when it comes to simulation work, we really do need to understand the workings of the world around us. This will naturally help us accurately re-create a dynamic motion and behavior of objects in a very believable way. For this reason, over the next few videos, we want to briefly touch on a number of laws or principles that govern objects in motion, laws and principles that really anyone wanting to work on dynamic simulations would need to have an understanding of. In fact, figuring out how things work in the real world would be an ongoing field of study for any serious simulation artist.

A look at gravity and drag

As a technical artist, when it comes to simulation work, we really do need to understand the workings of the world around us. This will naturally help us accurately re-create a dynamic motion and behavior of objects in a very believable way. For this reason, over the next few videos, we want to briefly touch on a number of laws or principles that govern objects in motion, laws and principles that really anyone wanting to work on dynamic simulations would need to have an understanding of. In fact, figuring out how things work in the real world would be an ongoing field of study for any serious simulation artist.

So, in this video let's give consideration to a couple of extremely important global environmental effects, these being gravity and drag. As we will tackle gravity first, we just need to make a quick disclaimer as neither Sir Isaac Newton nor Professor Albert Einstein were able to fully answer the questions of just what gravity is and how it actually works. We will be focusing in this instance on a discussion of the effects of gravity as we see them in a general sense here on earth. This, after all, is the premise upon which tools like MassFX work.

Gravity as a force determines that any object having mass, if suspended in mid- air and then released, will fall to the ground; hence the old adage, what goes up must come down. Objects come down at a fixed--that is, unchanging--rate of 9.8 meters per second squared. This is a constant value and it is essentially irrespective of mass. It is very true that when affected only by gravity, any two objects, no matter what their respective size and mass, should fall to earth at exactly the same constant speed, as we have mentioned, of 9.8 meters per second.

So, unless we are creating very unique or stylized situations, animations, then really all the objects in our dynamic simulation will need to be subject to the law of gravity. Getting this setting right is going to be critical to the finished quality of our simulations. If, then, all objects irrespective of mass should fall at the same speed under the influence of gravity, we may well ask why two very different objects, such as a feather and a brick, appear to fall at very different speeds.

Well, the answer is found in the second effect we want to consider here, which is drag, or air resistance. Air, or the atmosphere around us, can be thought of as an upward force of friction that acts against gravity; it slows down the rate at which an object will fall. If the structure or form of an object creates a lot of friction, as it would in our feather's case, then air resistance will slow it down very noticeably indeed. If an object's fall doesn't really create friction, as in the case of a brick, then air will have very little, if any, effect on it and so it will appear to fall faster.

However, if the feather and brick were dropped together in a vacuum--that is, an environment from which all air or cause of friction had been removed, but that was still subject to the law of gravity-- they would in fact fall at the same rate and hit the ground at the same time. Now, as the 3D environments in which our simulations will take place are, in reality, virtual vacuums with gravity enabled, we will need to use the tools available to re-create this atmospheric resistance, this drag. Again, this is going to be critical to the quality of our finished simulation.

Gravity and drag are two naturally occurring environmental effects that play a huge role in determining how objects move and react in the real world. We may, though, wonder about the objects themselves: Does the way that they are made or constructed affect their motion. Well, in our next video we will get an idea regarding the answer to that question as we take a look at volume, mass, and density.

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This video is part of

Image for Creating Simulations in MassFX and 3ds Max
Creating Simulations in MassFX and 3ds Max

51 video lessons · 2494 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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