Week 4 - Physics Based Animation Flashcards
What system is good for:
- Smoke
- Water
- Fire
- Sparks?
Particle Systems
What systems is good for cloth?
mass-spring models
What are the types of physics based animation?
Particles systems
mass-spring models
Out of scope:
rigid body simulations
Continuum mechanics
What is physics based animation?
Assign physical properties to objects like masses, forces, etc… Also procedural forces like wind
Then we simulate physics by solving equations of motion, this is realistic but hard to control
What Methods can be used for particle simulation? What do these methods always boil down to?
Methods for simulation range from heuristics that happen to look good, right up to full simulations.
For all methods they essentially boil down to a set of ODEs
What are the two methods for solving ODEs?
Newtonian method
Euler’s method
In the Eularian method, should you set the step size to the same value as the fps?
No, they are independent values
What is a major disadvantage to the Euler method vs newtonian method?
The Eulerian method may be inaccurate, like in a circular field where it will never form a full circle no matter how small the value of h (the step)
What’s a simple way of simulating smoke based on gravity?
We simulate smoke by using the simulation we normally use for gravity but turned upside down, this can be referred to as buoyancy
What is viscous damping? What is it used for?
Viscous damping is a force opposing the movement of a particle in a particle system proportionally to its velocity.
It can simulate wind resistance. It also removes energy which allows the system to settle, small amount of damping can stabilise the solver.
Lots of damping is also used to simulate viscous materials like honey.
What is a spatial field? What is it used for?
A spatial field is an externally specified velocity force (velocty field) which applies a force to particle p based on it’s position.
This has arbitrary function, could be wind, attractors, repulsers, vortexes. Can depend on time as well, can be procedural, could be used for procedural fluid flow.
Note that these add energy to the system, so some viscous damping may be needed to settle down before going forward.
What law is used in mass-spring simulations?
Hooke’s Law
What is the force in direction to a spring on a particle always proportional to?
the different of the length of the spring with its rest length
How much force does a particle experience in relation to a particle it is connected to with a spring?
Two particles connected by a spring experience the same force in opposite directions
When using a mass-spring simulation to simulate hair, what can you do to make that hair curly?
Make the deformation force proportional to the angle between segments
