---
title: mass
framework: gameplaykit
role: symbol
role_heading: Instance Property
path: gameplaykit/gkagent/mass
---

# mass

The resistance of the agent to changes in speed or direction.

## Declaration

```swift
var mass: Float { get set }
```

## Discussion

Discussion The higher the value of this property, the slower the agent will be to respond to goals that change its speed or direction, and vice versa. note: The simulation responsible for agent movement is based on realistic physical behaviors; however, this simulation is not connected to the physics subsystems in SpriteKit, SceneKit, or any other graphics engine. For example, setting the mass property of an agent does not affect the collision behavior of any SpriteKit physics bodies.

## See Also

### Constraining an Agent’s Movement

- [maxAcceleration](gameplaykit/gkagent/maxacceleration.md)
- [maxSpeed](gameplaykit/gkagent/maxspeed.md)
- [radius](gameplaykit/gkagent/radius.md)