
## What is it

The Compound is a special type of shape that acts as a "container" to other shapes. It allows modeling complex objects by using simple primitives, acheiving a better aproximation than using only one simple geometric shape.

## How to use

Imagine you have a mesh that represents a character. Character meshes are usually pretty complex, thus we want to avoid using it directly for collision. We can aproximate the shape of the character with a sphere representing the head, and a box representing the rest of the body. We will create two meshes to represent these shapes, parent them to the character mesh, create two child PhysicShapes and parent them to a PhysicsShapeContainer:

```javascript
const myMesh = BABYLON.SceneLoader.ImportMeshAsync(...);

const headNode = new BABYLON.TransformNode("headNode");
headNode.position.y = 3;
headNode.parent = myMesh;
const bodyNode = new BABYLON.TransformNode("bodyNode");
bodyNode.parent = myMesh;

const boxShape = new BABYLON.PhysicsShapeBox(new BABYLON.Vector3(0, 0, 0), new BABYLON.Quaternion(0, 0, 0, 1), new BABYLON.Vector3(1, 2, 1), scene);
const sphereShape = new BABYLON.PhysicsShapeSphere(new BABYLON.Vector3(0, 0, 0), 1, scene);

const parentShape = new BABYLON.PhysicsShapeContainer(scene);

parentShape.addChildFromParent(myMesh, boxShape, bodyNode);
parentShape.addChildFromParent(myMesh, sphereShape, headNode);

const body = new BABYLON.PhysicsBody(myMesh, scene);
body.shape = parentShape;
```
The following Playground shows a simple example of creating a Container body to approximate a mesh:
<Playground id="3H3DLR" title="Simple Physics Container example" description="Simple Physics Container example" />
            
The following Playground shows a comparison of using Container, Convex Hull and Mesh shapes on different meshes:
<Playground id="LKPBW5" title="Comparison of using Container, Convex Hull and Mesh shapes on different meshes" description="Comparison of using Container, Convex Hull and Mesh shapes on different meshes" />



# Physics Aggregate

## What is an Aggregate

The Physics Aggregate is a object that contains a Body and a Shape. It's a helper that allows creating all the objects necessary to physicalize your scene in just one call. In that sense, it's similar to Physics V1 Impostors, but with more control. Once created, you can easily get the individual parts and tweak them.

## How to use it

```javascript
const sphere = BABYLON.Mesh.CreateSphere("sphere", 16, 2, scene);
const aggregate = new BABYLON.PhysicsAggregate(sphere, BABYLON.PhysicsShapeType.SPHERE, { mass: 1 }, scene);
```

This is very similar to the Physics V1 Impostor.
At aggregate creation, a body and a shape are instantiated all at once. However, recreating shapes is not the most performant choice. You can alternatively pass the shape instead of the PhysicsShapeType, and the aggregate will reuse that shape:

```javascript
const sphere = BABYLON.Mesh.CreateSphere("sphere", 16, 2, scene);
const sphere2 = sphere.clone("sphere2");

const aggregate = new BABYLON.PhysicsAggregate(sphere, BABYLON.PhysicsShapeType.SPHERE, { mass: 1 }, scene);
const aggregate2 = new BABYLON.PhysicsAggregate(sphere2, aggregate.shape, { mass: 1 }, scene);
```


<Playground id="#4Y813L#1" title="Reuse shapes with Aggregates" description="Reuse shapes with Aggregates"/>

<Playground id="#Z8HTUN" title="Simple scene with Aggregate" description="Simple falling sphere created with an aggregate"/>

## Tweaking and accessing individual components

You can access the individual physics components by using the accessors:

```javascript
const aggregate = new BABYLON.PhysicsAggregate(sphere, BABYLON.PhysicsShapeType.SPHERE, { mass: 1 }, scene);
aggregate.body.setMassProperties({mass: 10});
```

## Disposing of an Aggregate

You can dispose of an aggregate by using the `dispose` method. This will dispose of the body and shape that were created by it, in case the shape was created by the aggregate. If the shape was passed as a parameter, then it will not be disposed, as it could still be in use by another body.



## How to use it

Both forces and impulses don't have any effect on bodies whose mass is 0.

```javascript
body.applyForce(
    new BABYLON.Vector3(0, 10, 0), // direction and magnitude of the applied force
    new BABYLON.Vector3(0, 0, 0) // point in WORLD space where the force will be applied    
);

// .... OR .....

body.applyImpulse(
    new BABYLON.Vector3(0, 10, 0), // direction and magnitude of the applied impulse
    new BABYLON.Vector3(0, 0, 0) // point in WORLD space where the impulse will be applied    
);
```

A reminder that, if a body's transform node contains Thin Instances, you can choose which instance to apply the force/impulse by passing `instanceIndex` as a parameter:

```javascript
// Apply a force to the first instance ONLY
body.applyForce(new BABYLON.Vector3(100, 0, 0), new BABYLON.Vector3(0, 0, 0), 0); 
```

If no index is applied, the force/impulse is applied to all instances.

## Difference between a force and an impulse

A force is a continuous effect that is applied to an object over time, which can change the object's velocity or direction of motion. For example, a force could be used to simulate gravity, wind resistance, or a player pushing an object.

An impulse, on the other hand, is a sudden, instantaneous effect that changes the velocity of an object. It is a specific amount of force applied over a very short duration of time, often modeled as a single frame in a game. For example, a collision between two objects might generate an impulse that changes the direction and speed of both objects.

In summary, a force is a *continuous* effect over time, while an impulse is a sudden, *instantaneous* effect that changes the velocity of an object. Click on the sphere in the following examples to experiment with forces and impulses

<Playground id="#R66K4K#1" title="applyForce" description="An example of using applyForce" category="Physics"/>

<Playground id="#Z8HTUN#677" title="applyImpulse" description="An example of using applyImpule" category="Physics"/>



## Physics Helper

The helper assists you with creating some phenomena like radial explosions or vortices.

```javascript
var physicsHelper = new BABYLON.PhysicsHelper(scene);

var origin = BABYLON.Vector3(0, 0, 0);
var radius = 10;
var strength = 20;
var falloff = BABYLON.PhysicsRadialImpulseFalloff.Linear; // or BABYLON.PhysicsRadialImpulseFalloff.Constant

var explosionEvent = physicsHelper.applyRadialExplosionImpulse( // or .applyRadialExplosionForce
    origin,
    radius,
    strength,
    falloff
);
// the second `radius` argument can also act as options: `.applyRadialExplosionImpulse(origin, { radius: radius, strength: strength, falloff: falloff })`

// or

var gravitationalFieldEvent = physicsHelper.gravitationalField(
    origin,
    radius,
    strength,
    falloff
);
// the second `radius` argument can also act as options: `.gravitationalField(origin, { radius: radius, strength: strength, falloff: falloff })`
gravitationalFieldEvent.enable(); // need to call, if you want to activate the gravitational field.
setTimeout(() => gravitationalFieldEvent.disable(), 3000);

// or

var updraftEvent = physicsHelper.updraft(
    origin,
    radius,
    strength,
    height,
    BABYLON.PhysicsUpdraftMode.Center // or BABYLON.PhysicsUpdraftMode.Perpendicular
);
// the second `radius` argument can also act as options: `.updraft(origin, { radius: radius, strength: strength, height: height, updraftMode: PhysicsUpdraftMode.Center })`
updraftEvent.enable();
setTimeout(() => updraftEvent.disable(), 5000);

// or

var vortexEvent = physicsHelper.vortex(
    origin,
    radius,
    strength,
    height
);
// the second `radius` argument can also act as options: `.vortex(origin, { radius: radius, strength: strength, height: height, centripetalForceThreshold: 0.7, centripetalForceMultiplier: 5, centrifugalForceMultiplier: 0.5, updraftForceMultiplier: 0.02 })`
vortexEvent.enable();
setTimeout(() => vortexEvent.disable(), 5000);
```

*For a more detailed explanation, please take a look at the playground example below.*

<Playground id="#E5URLZ#2" title="Physics helpers" description="Show how to use physics helpers and add various effects with forces" isMain={true} category="Physics"/>


Physics compounds

What is it

How to use

Further reading

Forces

Learn all about applying physical forces in Babylon.js.