When you’re working with physics simulations in Blender, seeing objects pass through each other can be frustrating. Many artists and animators expect realistic collisions, but sometimes, Blender’s physics collision just doesn’t work as planned. If you’re stuck with falling cubes that ignore the floor, or cloth that slips through other objects, you’re not alone. Let’s break down why this happens, how to fix it, and some tips to avoid common mistakes.
Understanding Blender Physics Collisions
Physics in Blender relies on mathematical models. When you add physics, Blender calculates how objects should interact — including collisions. There are different systems (Rigid Body, Soft Body, Cloth, Fluid), and each uses its own way to detect and respond to collisions. If something is not working, the cause is usually one of a few common settings or mistakes.
Most Common Reasons Collisions Fail
Many users miss small but critical options. Here are the top problems:
- Collision Not Enabled: The object needs the correct physics modifier (like Rigid Body or Collision).
- Wrong Object Type: Some physics types only work with specific objects (e.g., Mesh, not Curve).
- Incorrect Scale: Objects that are too big or too small can confuse the physics engine.
- Insufficient Steps: The simulation may skip frames, causing objects to “tunnel” through each other.
- Origin Point Issues: If the origin is far from the mesh, collisions may not register correctly.
Here’s a quick comparison of the most common blender physics types and their collision support:
| Physics Type | Collision Support | Common Uses |
|---|---|---|
| Rigid Body | Full | Falling objects, stacking, bouncing |
| Soft Body | Partial | Jiggly objects, cushions |
| Cloth | Specialized | Flags, clothing, curtains |
| Fluid | Custom | Liquids, splashes |
Credit: forum.godotengine.org
Step-by-step Fixes For Collision Problems
Blender’s flexibility is great, but it also means there are many settings to check. Here’s how to troubleshoot and fix collision problems:
1. Check Physics Modifiers
- Select your object.
- Go to the Physics tab.
- Make sure you’ve added the correct physics property (Rigid Body, Cloth, etc. ).
- For objects meant to be collided with (like the floor), add the Collision modifier.
2. Apply Object Scale
- Blender’s physics uses the object’s scale. If you scaled your object in Object Mode, physics may act strangely.
- Select your object, press Ctrl+A, and choose Scale.
- This applies the scale, making sure physics uses the right size.
3. Increase Simulation Steps
- Open the Scene Properties.
- Under Rigid Body World or the relevant simulation settings, find Steps Per Second and Solver Iterations.
- Increase these values (try doubling). This helps prevent fast-moving objects from missing collisions.
4. Adjust Collision Margins
- Every physics system has a Margin setting (often hidden in the collision settings).
- Try increasing the margin slightly. Too small or too large can both cause problems.
- For rigid bodies, a margin of 0.04 is usually a good start.
5. Check Object Types And Meshes
- Only Mesh objects work with most collision systems. Convert curves or other types to mesh if needed.
- Very complex meshes can slow down or break collisions. Try simplifying the mesh.
6. Reset Origin And Apply Transforms
- The origin should be near the center of the mesh.
- If not, go to Object > Set Origin > Origin to Geometry.
- Also, apply rotation and location transforms.
Deeper Troubleshooting: Non-obvious Issues
Most beginners overlook these advanced causes:
- Non-Uniform Scale: If the X, Y, and Z scales are different, physics can act weird even if you apply scale later. Always check for uniform scaling.
- Hidden Modifiers: Some modifiers (like Subdivision Surface or Mirror) can change the mesh shape after collision calculation. Apply or move these modifiers as needed.
- Animated Colliders: If the object you want to collide with is moving (like an animated floor), make sure it is set as a passive rigid body and animated using keyframes, not physics.
Here’s how different collision margins and simulation steps affect results:
| Setting | Low Value | High Value | Effect |
|---|---|---|---|
| Collision Margin | 0.001 | 0.1 | Too low: objects clip, too high: hover above surfaces |
| Steps Per Second | 60 | 240 | Low: objects miss collisions, High: smoother but slower |
| Solver Iterations | 10 | 100 | Low: unstable stacking, High: more accurate |
Credit: docs.blender.org
Example: Fixing A Simple Collision Problem
Imagine a ball falling through a plane instead of bouncing. Here’s how you’d fix it:
- Select the plane, add a Collision modifier.
- Select the ball, add a Rigid Body property (type: Active).
- Apply the scale for both objects.
- Increase steps per second to 120.
- Set collision margin to 0.04.
Now, run the simulation. The ball should bounce as expected.
Two Insights Beginners Often Miss
- Order of Modifiers Matters: The modifier stack affects the final shape used for collisions. If Collision is below a Mirror or Subdivision modifier, the wrong shape is used.
- Outdated Blender Versions: Sometimes, collision bugs are fixed in new Blender releases. Always check if you’re using the latest version, as physics systems get regular improvements.
When To Use Different Collision Types
Blender offers several collision shapes for rigid bodies:
| Shape Type | Performance | Accuracy | Best For |
|---|---|---|---|
| Box | Very Fast | Low | Simple boxes, crates |
| Sphere | Fast | Medium | Balls, round objects |
| Convex Hull | Moderate | High | Irregular shapes |
| Mesh | Slow | Very High | Complex, accurate needs |
Choosing the right one improves both speed and accuracy.
Reliable Resources
To learn more or check updates on Blender physics, visit the official Blender Manual.
Credit: extensions.blender.org
Frequently Asked Questions
Why Do My Objects Fall Through The Floor In Blender?
Most likely, the floor does not have a Collision modifier or is not set as a passive rigid body. Make sure both objects have correct physics settings.
How Can I Fix “tunneling” Where Fast Objects Pass Through Each Other?
Increase the Steps Per Second and Solver Iterations in simulation settings. Higher values give Blender more chances to detect collisions.
Do Modifiers Like Subdivision Affect Collisions?
Yes. The order of modifiers changes the collision mesh. Place Collision above shape-changing modifiers, or apply them before simulating.
Is There A Way To Visualize Collision Meshes?
Enable Bounds display in the viewport, or use the Collision display option. This helps you see if the collision shape matches the visible mesh.
My Collision Works In Some Frames But Not Others. Why?
This usually happens with animated colliders or low simulation steps. Make sure all transforms are applied, and boost simulation accuracy as needed.
Getting Blender’s physics collisions right can be a puzzle, but understanding these settings will save you hours of frustration. With careful setup and a few expert tweaks, you’ll see realistic interactions every time.
Dorothy Addeo is a senior product reviewer at Safefins.com with years of experience testing kitchen, furniture, backpacks, and everyday lifestyle products. She focuses on comfort, durability, usability, and long-term value through hands-on research and real-world testing. Her goal is to help readers find reliable products with honest, easy-to-understand recommendations they can trust.