I’ve been working with PhysX PBD materials in IsaacSim and came across two parameters: Drag and Damping. While I understand that both of these relate to forces that resist movement, I’m a bit confused about how exactly they differ and how each parameter affects the simulation.
Could someone help clarify what these parameters specifically control in a PhysX PBD material? For example:
How does Drag affect the simulation? Is it related to resistance to motion through a medium or something else?
What role does Damping play in the PBD material? Is it linked to internal energy loss or another kind of resistance?
Are there specific scenarios where adjusting one is preferred over the other?
From my observations, when I let cloth objects free fall, Drag results in an overall lower velocity when using the same numerical values as for Damping (see Figure). However, I noticed that Damping also affects the velocity of the entire object, which contradicts my understanding of damping. I thought Damping should primarily result in internal energy losses within the material, without directly impacting the velocity of the entire body in free fall. This has left me wondering about their underlying mechanics and intended usage.
Any insights or examples would be much appreciated! Thanks in advance for your help. 😊
Thank you for the suggestion, but I’ve already reviewed the Particle Simulation — Omniverse Extensions documentation. Unfortunately, it didn’t fully clarify the specific implementation differences between the Drag and Damping parameters
Apologies for the delayed follow-up. Here’s the explanation of how these parameters differ in PhysX PBD:
Drag — Applies a velocity-dependent force that resists each particle’s motion relative to the world/medium. Think of it as air resistance. In free fall, drag directly opposes the downward velocity of the entire cloth, slowing its descent. The
force is proportional to each particle’s absolute velocity.
Damping — Applies a velocity-dependent force that resists each particle’s motion relative to its neighbors. It’s designed to dissipate internal deformation energy (oscillations, stretching, flapping). However, in PhysX PBD’s implementation,
damping is applied as a per-particle velocity reduction factor (exponential decay per step), which means it also affects uniform/rigid-body motion — not just relative motion. This is why you observe it slowing free fall too.
Why both affect free-fall velocity (your observation):
Your observation is correct and is a known characteristic of the PhysX PBD implementation. Ideal damping (only dissipating relative/internal motion) would require computing velocity differences between connected particles and only damping
those. The current implementation uses a simpler per-particle velocity scaling, which is computationally cheaper but has the side effect of damping rigid-body motion as well.
Practical guidance:
Use Drag when you want to simulate aerodynamic resistance (cloth falling through air, underwater motion)
Use Damping when you want to reduce oscillations/jitter in the cloth without adding environmental resistance
At equivalent numerical values, Drag has a stronger effect on bulk motion (as your figure shows) because its force model is explicitly velocity-proportional, while Damping applies a multiplicative factor
