The weighing scales in my kitchen are currently showing 0 Kg. However, there is a column of air between the scales and the ceiling that is presumably exerting pressure on them. If I were to place those scales in a vacuum, would those scales show a negative weight?
They would show only a very tiny
EDIT: When there's atmosphere, there's a buoyant force pointing up. When we lose atmosphere, there's more force down and the tared scale now reads positive. Originally I got the buoyant force correct but the reading on the scale backwards.
It would vary from weighing scale to weighing scale. In my experience, most of the scales subtract the weight of the "tare", which is the thing that you put your "thing to be weighed on". The scales which use this system will show a noticeable amount of negative weight.
However the types which do not subtract the amount of dare, rather compare it with some "example" weight will not be affected much.
Some scales are more sophisticated and completely ignore the initial dare by some methods. They, also, would not exhibit much difference in any gravity or pressure change.