How to Launch a Part Up no Matter the Size

Is there a way to apply Velocity onto a part and have it go in that direction no matter how big it is instead of using ApplyImpulse?

VectorForce would apply a consistent force to the part.
Not sure what you mean by ‘big’, I assume you refer to part.Mass so you would need to multiply the VectorForce by the mass if you wanted consistent speeds for all size parts.
You could do the same with ApplyImpulse as well, if you wanted a simple burst of acceleration.
If you wanted to simply move the part without physics you would only need to adjust the part’s CFrame, which you could do via tweenService.

just use BasePart.AssemblyLinearVelocity

Doesn’t make a difference to the op. It doesn’t matter if he uses Velocity or AssemblyLinearVelocity, that’s out of the question.

But, for the answer, multiply the velocity by the part’s mass, and mess around with it for a golden value. If you’re trying to get a constant velocity, use a LinearVelocity, set the MaxForce to math.huge, set VectorVelocity to the direction, create an Attachment, parent it to the part, then set the Attachment0 of the LinearVelocity to the new attachment, and finally, parent the LinearVelocity to the attachment