# Tagged Questions

Rigid body dynamics is the simulation of physical objects which are "solid" and cannot deform or change shape during simulation.

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### Difference between Update method and FixedUpdate in Unity?

i am starting to learn Unity3d and one of the confusion i get is difference between Update() and FixedUpdate(). I am following Lynda Unity 2D game development tutorial there, the instructor uses ...
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### Why do objects interpenetrate in this simple collision solver?

The code below is from a Microsoft XNA sample here. This is quite a simple rigid body simulation that ignores many physical effects (such as angular momentum), but it does try to push objects (spheres)...
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### Calculating impulse propagation through a rigid body after a collision

I'm working on a game. I need to work out what the impulse is at different points on a body as a result of a collision. For example, in the following diagram, if there is a collision that results in ...
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### How can I implement fixed joints in a 2D physics system?

I'm developing a simple, 2D physics system to complement an entity/component game object framework. So far, I have implemented some basic, tutorial-level physics. An entity that is affected by physics ...
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### How to detect collision in Unity3D without rigid bodies?

The target platform of my game is mobile devices therefore I try to develop it performance oriented. It will be a strategy game so I don't really need physics in it, consequently I did not add ...
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### Kinematics of a die roll?

I'm working on a simple 3D game. In the game, sometimes the players have to roll die (a D8 to be exact). I wish to represent the rolling die with a 3D model, and I'd like to animate it in 3D space as ...
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### Calculating impulse with multiple collision points

In my amateur 2D rigid body physics engine for a game I react on collisions between two bodies with an impulse j (formula 11) as explained here. To calculate this impulse I need one contact point P ...
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### Creating stable tentacle structures

I am using verlet integration to simulate some tentacles. So far it works great and I am satisfied with how it looks in general. Here is how a tentacle is built: The very stiff sticks are colored ...
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### Procedural generation of physics-enabled structures (in a 2D world)

Is it possible to procedurally generate stable structures out of rigidbody objects at a reasonable runtime speed? Imagine Angry Birds's levels kind of structures but generated procedurally.
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### In Unity3D, what is the relation between inertiaTensor and inertiaTensorRotation?

In unity3d there are two properties on rigidbody that correspond to the moment of inertia tensor. One of them is: rigidbody.inertiaTensor, which I know is the diagonal of the inertia tensor, The ...
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### Stopping 3D object in place

I am at 1.2 stage (moving the player) at Unity course "Roll-a-ball" and have question: I want to add feature that stops a player and sets his new position on 0, 0, 0. I can reset the position, but I ...
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### Unity 4 - Some Rigidbodies Won't Fall Asleep

I'm having this problem in the free edition of Unity 4.1 where rigidbodies aren't falling asleep (and yes, I've tried playing with the sleepVelocity and sleepAngularVelocity values!). I've read the ...
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### Adjusting a skeleton to a Specific Stance

Imagine having a climbing wall and you take 4 adjacent handholds and footholds where together they create a stance. Is there any algorithm or technique with which it would give you a realistic human ...
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### How can I implement revolute (hinge) joints in a 2d physics system?

Further to my previous question on fixed joints, I am now going toe-to-toe with hinge joints in 2D physics. Though the answer to the previous question was excellent, I have come across a few problems ...
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### Physics: calculating angular acceleration in world vs local space

I have a pretty simple rigid body simulation written in Python. In my code I calculate the angular acceleration using formula: angAcc = torque * inertiaTensor^-1 (note row-major matrix order) Now, ...
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### Rigidbody physics concept: Why translate collision shape on-the-fly instead of mutating it?

Crossposting at http://stackoverflow.com/questions/29993547/rigidbody-physics-concept-why-translate-collision-shape-on-the-fly-instead-of-m I've spent some time going through physics engine's ...
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### Understanding Unity3d physics: where is the force applied?

I'm trying to understand which is the right way to apply forces to a RigidBody. I noticed that there are AddForce and AddRelativeForce methods, one applied in world space coordinate system meanwhile ...
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### Getting one rigidbody to follow another, but still react to stuff Unity3D/C#

Basically what I'm doing is having a ball you can pick up and drop on a ramp. When you pick up the first ball, the second ball follows close behind, and when you drop the first ball on to the ramp the ...
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### How can I ensure character weapon is also included in collision detection?

I have two models, my player character and her weapon. Each can be controlled independently (that is, I allow the player to aim the weapon). The object hierarchy is: Character (with ...
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### Can I make a character solid but not lose non-physics behaviour?

My character can walk around in the world, but walks through other objects, for example a cylinder (stand-in for a cannon). To fix this I added a capsule collider to each of the character and cylinder,...
895 views

### Inverse Explosion with Unity2d

I am currently trying to make all other objects push away from the player when the player explodes. It currently works, but it pushes close objects a little and far objects very far. What I want is ...
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### bullet character controller sliding down any slope gradient

I've been experimenting with the btKinematicCharacterController. I've seen very old complaints that it has issues but I can't find anything recent stating that these issues remain (and nobody ever ...
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### Getting the Volume of an Uneven Mesh

Let's say I have a cube, and that cube breaks apart into 100 different unevenly sized pieces. How can I get the volume of each of those pieces compared to the cube's volume? Using this in order to ...
471 views

### Jumping higher when the player touches a trigger collider in Unity

Im using Unity engine to create a 2D platformer. My character can single/double jump, this works fine everywhere except when i am in range of a collider with a IsTrigger set to TRUE, then my character ...
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### How can I trigger an event each time the rotation of my rigidbody2D is at a given value?

I would like to trigger an event each time my rigidbody2D is at a particular value. The event should only be triggered once for each given value per complete object revolution. Initial attempts at ...
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### How can I add an impulse to specific rigid bodies at rest?

Scenario Rocks falling down a rocky slope, with a flat surface at the bottom. When they land on the surface, the rocks move slightly before coming to a rest. GLESDebugDraw shows the bright orange ...
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### In Unity3D (and PhysX), how do I calculate the products of inertia?

Since unity3d uses physx underneath the surface, obviously they share the same features. One of the features is the moment of inertia tensor - Unity3D one, PhysX one. Though, they use the diagonal ...
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### Keep gravity velocity the same all the time

I have 2D rigidbodies that fall to the ground, however they speed up while falling. Also, when they freeze in the air and then unfreeze, the velocity is set to 0 and they gradually start speeding up ...
610 views

### Why does my RigidBody collision fail depending on which entity is moving?

I am working on a UDK project and have a collision problem. I have a Crate which is a kActor with RigidBody physics and my player who is a Pawn. When my player moves and collides with the crate, the ...
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### Inverse Dynamics How to [closed]

I have some motion capture data (kinect) that records all body joints (32fps) and I want to take particular positions (for example when a person moves both of his hands up in the sky in celebration ...
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### How to move rigidbodies

Have i understood this correct: If i want to use a rigidbody for physics then i should not move an object through its transform.position. I should never move it by riigidbody.velocity since i then ...
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### How to freeze rotation with a Rigidbody 2D? [closed]

So I am looking to freeze rotation in the Y axis on a Rigidbody 2D. I'm not sure how to set this in my code. This is what I have so far, can you point out my errors? public class PlayerMovement : ...
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### Calculating the angular momentum of rigidbody in Unity3D

Knowing that angular momentum in 3D is L = Iω (moment of inertia times angular velocity), how do I calculate it in video game world? In unity3d I have the diagonal inertia tensor rigidbody....
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### How to slide a non-kinematic rigidbody?

I'm studying Unity3d, coming from a 2d background, and I'm a bit confused how some things work. I'd like to slide a non-kinematic rigidbody, i.e. "just move it forward", like if it was hovering over ...
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### How to destroy bullet on collision but only after it makes the collided object to bounce?

I made a scenario that shooting a bullets on crates make them both bounce nicely (both the bullet and crates are RigidBody2D & Colliders). When I use OnCollisionEnter2D to destroy the bullet when ...
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### Unity: Adjusting 2D physics for different mobile resolutions

I created a test project to see how different mobile resolutions affects Unity's 2D Physics. They way I handled the resolutions was to contain all the objects (including non-UI objects) in a Canvas ...
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### Lots of bouncing balls sink into each other [closed]

I'm trying to model a system that simulates an arbitrary number of bouncing balls with some gravity. So far I've come up with a solution that can be seen here: https://github.com/ahahalol/...
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### How could I get composite rigid body into unity

I am developing a game, in unity, that has accurate destruction physics and from my understanding unity uses plain old rigid body physics. I was wondering if there was a way to bring composite rigid ...
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### Warp GameObject Size When Entering/Leaving Area

Below I have an image describing the desired functionality I am going for. Let's say you control a square and when you move this square into a given area, any part of your rigidbody/model inside of ...
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### Jump without bouncing in physics engine

I am using Ogre3D as my rendering API, and OgreBullet as my physics engine. I have an test entity that when the y part of the velocity is 0 and spacebar is pressed, the velocity changes to, lets say: ...
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### Strange behavior of RigidBody with gravity and impulse applied

I'm doing some experiments trying to figure out how physics works in Unity. I created a cube mesh with a BoxCollider and a RigidBody. The cuve is laying on a mesh plane with a BoxCollider. I'm ...
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### Dynamic body implementation

I am writing a 2D game where one of the characters has some very particular requirements. This character is a body with no particular shape (similar to a fluid, but not so much), it has to be able to ...
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### How would joints work in an impulse-based physics engine?

I want to learn about physics engines, especially impulse-based ones. So I've followed along this tutorial to create some simple rigid-body physics: http://gamedevelopment.tutsplus.com/tutorials/how-...
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### Handling movement on sloped surfaces - clamping character to sloped surface

I've noticed that a lot of people seem to have this issue but I've yet to find an actual working solution - when a rigidbody-based character controller (I'm not using Unity's character controller) ...
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### Changing speed of an object

Is there a way of changing speed of an object at certain time? I want to change my speed to my initial speed after colliding with any object. I have already added bounce Physics to my colliding ...
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### Should I compute impact damage with energy or momentum?

My game uses physics (Box2D in particular). Just about every object in the game can be destroyed, and the primary method of combat is by slamming objects into one another at high speed. It makes ...
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### Colliders for moving inside a spaceship when the whole spaceship is made of a single mesh (in Unity)

I've begun to study a unity engine in one purpose: I have a great multi player game idea! The main essence: In space there are two (or even more) huge spaceships with crew consisted of players (all ...
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### Increasing friction or Adding force relative to transform position in Unity 2D?

Back again with a quick question! I have a few basic platforming mechanics going on in this scene. I have a prefab platform with an animation that loops back and forth between two different x ...