Physics Material Restitution property ignored in Newton Physics ( MuJoCo ) ?

[SebastienTixierKWA]

Hello,
I unziped the binaries windows 6.0.1 version
I am testing MuJoCo in isaac 6.0.1. I launched using isaac-sim-newton.bat
I create the simplest scene : PhysicsScene, Ground Plane, Shape->Sphere, Physics->PhysicsMaterial->Rigid Body Physics Material.
Set the restitution of the physics material to 1
Add Physics->Rigidbody and Collider Presets to the Sphere
Place the sphere 1m high, assigned the physics material to the sphere collider.

Click play, the sphere do not bounce just a very little bit ( like 1mm ), whatever restitution property I set.

I tried to use the Compliant Contact properties in the Physics Material -> Advanced, it didnt do anything.

What am I doing wrong?

Cheers,

Seb

[PeterL-NV]

Hi, Your scene is set up correctly — this isn't something you're doing wrong, it's a solver behavior. Because you're running the Newton backend with the MuJoCo solver (that's Newton's default solver), and MuJoCo handles contacts very differently from PhysX:

• MuJoCo resolves contacts with a soft/compliant constraint model (solref/solimp), which is inelastic by default — it has no coefficient-of-restitution ("bounciness") the way PhysX does.
• In the current Newton integration, the MuJoCo solver doesn't expose a restitution parameter at all, so the restitution value on your Physics Material is effectively ignored under MuJoCo. That's why changing it from 0 to 1 makes no difference and the ball just settles.
• (The "Compliant Contact → Advanced" settings map to contact stiffness/damping, not restitution, so they won't give you a bounce either.)

So the restitution isn't being applied — expected for MuJoCo, not a bug in your scene.

Currently only the MuJoCo solver is supported for the Newton backend in Isaac Sim, so if you want a bouncing sphere, you will need to switch to the PhysX backend.

[SebastienTixierKWA]

Hello Peter.
Thanks for your answer, we are currently evaluating physics in Isaac Sim, already made my assessment using PhysX, now I am testing newton physics, so I don't really 'need' a bouncing ball for now, just tried to evaluate the pro and cons of each physics solver.
Now I know I didnt do anything wrong, and I guess that's something that would be added in the future: the elasticity of the physics material for newton physics.
Cheers,
Seb

[PeterL-NV]

Hi, if you're interested on updates from Newton, please keep an eye on the newton-physics repo, and you can also file issues there if it's related to Newton.
I'm closing this discussion.