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# isAffectedByGravity

A Boolean value that determines whether gravity, as defined by the scene’s physics simulation, affects the motion of particles.

```
var isAffectedByGravity: Bool { get set }
```

## Discussion

Gravity applies a constant acceleration to all particles in the system. SceneKit offers two options for simulating the effect of gravity on particles:

- The [`isAffectedByGravity`](/documentation/SceneKit/SCNParticleSystem/isAffectedByGravity) property, which uses the [`gravity`](/documentation/SceneKit/SCNPhysicsWorld/gravity) vector specified by the [`physicsWorld`](/documentation/SceneKit/SCNScene/physicsWorld) object of the scene containing the particle system. Use this option when you want the system’s particles to be affected by the same gravity as the [`SCNPhysicsBody`](/documentation/SceneKit/SCNPhysicsBody) objects in your scene.
- The [`acceleration`](/documentation/SceneKit/SCNParticleSystem/acceleration) property, which is independent of the simulation SceneKit uses for physics bodies in the scene. Use acceleration to simulate gravity if you have no [`SCNPhysicsBody`](/documentation/SceneKit/SCNPhysicsBody) objects in your scene, or if you want particles to be affected both by the physics world’s gravity and another constant acceleration (such as wind).

The default value is <doc://com.apple.documentation/documentation/Swift/false>, specifying that the physics world’s gravity does not affect particles.

---

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