BasePart.AssemblyLinearVelocity

The linear velocity vector of this part's assembly. It's the rate of change in position of AssemblyCenterOfMass in studs per second.

If you want to know the velocity at a point other than the assembly's center of mass, use GetVelocityAtPosition().

Setting the velocity directly may lead to unrealistic motion. Using a VectorForce constraint is preferred, or use ApplyImpulse() if you want instantaneous change in velocity.

If the part is owned by the server, this property must be changed from a server Script (not from a LocalScript or a Script with RunContext set to Enum.RunContext.Client). If the part is owned by a client through automatic ownership, this property can be changed from either a client script or a server script; changing it from a client script for a server-owned part will have no effect.