--- title: LinearVelocity description: The LinearVelocity constraint applies force on an assembly to maintain a constant velocity along a 3D vector, line, or 2D plane. --- For an overview on creating, visualizing, and simulating mover constraints, including `Class.LinearVelocity`, see [mover constraints](../../physics/mover-constraints.md). Also see [Roblox units](../../physics/units.md) to understand how Roblox units compare to metric units. A `Class.LinearVelocity` constraint applies force on an assembly to maintain a constant velocity. It can be set to apply force along a `Datatype.Vector3`, line, or 2D plane.

The `Class.LinearVelocity` constraint applies a force that attempts to maintain a **constant** linear velocity. If you want to control the amount of force applied, use a [VectorForce](../../physics/constraints/vector-force.md) constraint. Alternatively, if you only need **initial** linear velocity, set the `Class.BasePart.AssemblyLinearVelocity|AssemblyLinearVelocity` property directly on the assembly. ## Relativity Application of velocity can be controlled through the constraint's `Class.LinearVelocity.RelativeTo|RelativeTo` property. If set to `Enum.ActuatorRelativeTo|World`, force will be applied in world coordinates, independent of the parent or attachment orientations. If set to `Enum.ActuatorRelativeTo|Attachment0` or `Enum.ActuatorRelativeTo|Attachment1`, force will be applied relative to `Class.Constraint.Attachment0|Attachment0` or `Class.Constraint.Attachment1|Attachment1` respectively.

RelativeTo = **World**

RelativeTo = **Attachment0**