a measure of the weight (which is what a regular scale measures) gives us directly the mass.
To measure mass in space, we have to use another kind of scale, which is called an inertial balance. An inertial balance is made of a spring on which you attach the object whose mass you’re interested in. The object is therefore free to vibrate, and for a given stiffness of the spring the frequency of the vibrations enables the scientists to calculate the mass.
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https://physics.stackexchange.com/questions/138297/can-mass-be-directly-measured-without-measuring-its-weight
The current devices for measuring mass (be it weighing scale, mass balance etc) all works by measuring the force rather than the mass (since g is assumed to be constant, F α m).
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Does air weigh anything?
https://indianapublicmedia.org/amomentofscience/heavy-air
http://www.slate.com/blogs/bad_astronomy/2014/08/18/helium_how_do_you_weigh_a_balloon.html
