# Difference between Rigid Body and Dynamic?

I’ve just been wondering what the difference is between Rigid Body and Dynamic, since the old versions of blender (i don’t remember exactly what version they stopped this) had both of them as buttons you could set. Now its only selectable in a drop down menu, therefore only allowing you to select one, and not the other.

Rigid Body physics tilt and rotate while Dynamic objects don’t. Think like the difference between an anvil who falls onto the ground and a block - the block will tilt and roll, while the anvil would just fall upright. In reality, the anvil, too, is rigid body - it’s just that for imagination purposes, the anvil doesn’t roll.

This is how I understand it.

The user could work without bullet and write all their own methods to impart gravity and collisions with transfer of momentum and angular momentum. As they built a collection of scripts and objects they’d effectively have their own physics engine. But the author of Bullet has done it for you and presents it for you in such a way that you only select what you need when you need it, because the fact is that it is cpu expensive.

What can be confusing for the beginner is that the term Dynamic suggests that the object is more versatile than a Rigid Body. But a dynamic object actually has a subset of the capabilities of a rigid body object. The difference between them is that the rigid body can have angular motion imparted to it without the user having to explicitly apply angular motion to it. In other words they will tumble or “overbalance” and rotate as they fall without the user having to apply rotation. (And you could only ever select one or the other.)

For me, I like the challenge of making minimal use of Bullet. For fun you can select no physics, no collisions and then try to create a simple scene that exhibits realistic physics and collisions. Make use of your high school maths. As you’re doing it you begin to understand what the author of Bullet has done.

In a nutshell
Rigid Bodies- Rotate
Dynamic-Don’t Rotate

Also - Rigid body eats more frame rate than dynamic objects, at least in my experience.

3Dmedieval is correct - rigid body physics are harder to calculate than dynamic, but it isn’t too bad on the CPU as long as you’re not using a complex physics mesh. Simper is better when it comes to physics. EDIT: And everything else in game design.