Well in computer terms 1 can be a very big number as a reference to mass.
Google check an empty balloon has a mass of .012 kg.
Assuming that a physics base result is required then all elements as to the math has to match the real world equivalent.
Or
You can cheat and give the object in question a positivity gravitation value.
And as a though. You did tell UE4 that the object was a movable right?