ApplyImpulse and AssemblyLinearVelocity doesn't work

I don’t know what else to say. This is the code:

part.AssemblyLinearVelocity += Vector3.new(1000,0,0)

It’s done in a module script that is required with a localscript. Usually, network ownership would interfere here, but the client owns the part entirely…

The absurdly high number is just for testing, but it doesn’t seem to do anything. Any ideas? I tried changing += to =, and *=, but that didn’t help.