Monthly Physics Tricks

A Few Things About The Engine Workflows

The way most people approach Monthly Physics Tricks is completely backwards. They spend three weeks trying to tune the mass scaling on rigid bodies before they even understand what the solver is doing under the hood. I ran into this constantly when I was still building content for that indie studio in 2019. We had one developer who refused to believe the engine was at fault when his destruction scenes kept soft-clipping. Turns out he hadn't enabled sub-stepping and was running the simulation at 30Hz with objects moving at 400 meters per frame. The trick isn't in the presets. The trick is knowing when to override them. At its core the system is just a collision resolution loop with some added heuristics for object stability. But the heuristics are where everything falls apart if you don't understand the trade-offs. The default settings will keep your scene stable, yes. But they also introduce a visible amount of positional drift that becomes obvious the moment you try to do precise stacking or alignment. I learned this the hard way when a client asked me to recreate a cathedral interior with hundreds of floating book models. The default solver pushed every book approximately 2 millimeters per second toward the center of the scene. That sounds harmless until you're rendering at 8K and those books have been "drifting" for forty-five seconds of simulated time. The workaround was to write a small custom constraint script that anchored the Z-axis position while leaving the X and Y free. Saved me two days of manual adjustment and another day of explaining to the client why his floating library looked like a swarm of birds. The solver itself runs on a semi-implicit Euler method by default. That means it approximates velocity changes across each time step rather than solving the full differential equation. It's fast, which is why it's the default. But the approximation error accumulates. When you're working with Monthly Physics Tricks you need to decide early whether accuracy matters more than frame budget. There's no middle ground that feels right. I usually recommend starting with the default and only increasing solver fidelity for the specific objects or regions that actually show the problem. You don't need a higher fidelity solver for a background prop that will never interact with anything meaningful.

Common Pitfalls That Waste Days

The biggest mistake I see is over-relying on the automatic friction and restitution values. The defaults are designed to prevent objects from sliding forever, which is fine for general use. But they create this weird sticky behavior when you're trying to do anything that requires smooth sliding motion. A simple table surface with a default friction coefficient of 0.5 will make a sliding object come to a near-halt within two meters. If you want a proper marble-or-bowling-ball feel you're looking at something closer to 0.05 to 0.1 depending on the scale. And yes you have to test this yourself. The published values in the documentation are for a reference scenario that doesn't match most real projects. Another thing nobody warns you about is the interaction between continuous collision detection and the broad-phase spatial partitioning. When you enable CCD on fast-moving objects the engine has to run additional sweep tests every frame. On a scene with fifty or more fast objects at once you'll see the frame time jump from roughly eight milliseconds to somewhere around forty-five. That's not a typo. I hit this exact wall last year when I was simulating a rain effect on a city street and every raindrop had CCD enabled because otherwise they'd tunnel through the awnings. The fix was to selectively disable CCD on drops that were more than thirty meters from the camera and rely on the coarse spatial partitioning to catch the close ones. Dropped the overhead from forty-five milliseconds back down to twelve.

How I Actually Approach a New Scene

I don't start by tweaking numbers. I start by understanding what the final output needs to look like. Is this something that will be viewed at rest or in constant motion. Does it need to be physically accurate or just convincingly physical. Those two questions determine everything that follows. For a still architectural visualization I'll crank the solver iterations up to six or eight and accept the render time hit. For an interactive demo that needs to run on mid-range hardware I'll drop to three iterations and work around the instability with custom constraints. The constraint system in Monthly Physics Tricks is honestly the most underrated part of the whole pipeline. Most people treat it as a last resort. I treat it as the first tool I reach for. A well-placed angular constraint can replace an entire chain of connected rigid bodies that would otherwise take ten times longer to stabilize. I recently replaced a thirty-object chain simulating a hanging rope with a single chain constraint node and two anchor points. The result looked identical frame for frame and ran at roughly a fifth of the computational cost. The trick is learning the limits of what the constraint system can handle before you build around it. It struggles with twisting forces and tends to introduce oscillation artifacts when the constrained objects move too fast relative to their connection points. There's also the matter of object grouping. When you have twenty-plus objects that interact heavily with each other the engine can group them into a single compound object to reduce the collision pair count. This is a massive performance win but it fundamentally changes how those objects behave. They stop being able to tumble independently. A bag of rocks becomes a single solid mass. I've seen this trip up people who don't realize they've accidentally grouped objects during the import process. The fix is to check the object hierarchy and verify grouping settings before you spend any meaningful time tuning individual properties.

When It Just Doesn't Work

Sometimes the right answer is not to use Monthly Physics Tricks at all. If your scene involves fluid-like behavior, large-scale particle systems, or deformable meshes, the rigid body solver is the wrong tool. I once had a client insist on simulating a collapsing sandcastle using only the physics engine. It took three weeks, required five separate workarounds, and still looked nothing like sand. We ended up replacing the entire simulation with a baked geometry morph and a few emission texture animations. The result was indistinguishable to the viewer and took about four hours to produce instead of three weeks. Know when to walk away from the solver. That's not a failure of skill. That's a failure of judgment, and fixing that is what separates people who ship work from people who burn through deadlines. Export formats also deserve more attention than they get. The default export path will lose custom constraint data and solver overrides. If you're handing off a scene to someone else or archiving it for later revision you need to use the full project export, not the simplified mesh dump. I lost an entire month's worth of work once because I exported to a format that didn't preserve the constraint hierarchy. Everything looked correct visually but the simulation was completely uneditable on the receiving end. The file was two hundred megabytes and every single custom tweak was gone. Make sure you understand what each export option actually preserves before you commit to it.