Note: our Young's modulus is divided by density (on purpose)

[ryichando]

A heads-up about how young-mod works in this solver, so nobody is surprised.

Strictly speaking, Young's modulus is a material property in pascals and should not depend on density. In our solver, though, we intentionally divide it by density. This is a deliberate design choice, not a bug.

Why we do it

Dividing stiffness by density makes a single object's motion stay the same when you only change its density. So you can adjust how heavy something is without having to re-tune its stiffness to keep the same look. That decoupling is convenient and is the behavior we wanted.

What this means for you

• The young-mod value is not a textbook Young's modulus in pascals. Plugging in a real material value from a reference table will not give you that material's real stiffness.
• If two objects have different densities, their stiffness is scaled differently, which matters when they interact.

We are sharing this so you know what the number actually represents. Questions and feedback are welcome below.

[Geetaur]

@ryichando Is it possible to have this as a toggle option?

[ryichando]

@Geetaur Sure! I will make a new feature request for this.

Edit: #60

[Geetaur]

@ryichando Thank you! Can we assume that the other parameters are physical without any sort of scaling applied?

[ryichando]

@Geetaur Yes, with one caveat: the density unit depends on the object type. For solids, density is given in kg/m³; for shells, it is kg/m²; and for rods, it is kg/m.