# Measuring Mass In Weightless Space... **URL:** \ **Category:** Factual Questions\ **Created:** [November 16, 2016, 3:54pm UTC](https://boards.straightdope.com/t/measuring-mass-in-weightless-space/772169 "2016-11-16T15:54:03Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Jim\_B](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jim_b/32/4338_2.png) [@Jim\_B](https://boards.straightdope.com/u/Jim_B)\ **Post date:** [November 16, 2016, 3:54pm UTC](https://boards.straightdope.com/t/measuring-mass-in-weightless-space/772169/1 "2016-11-16T15:54:03Z")
Something I have wondered for a long time. And if you all will indulge me, I will even offer my own, possible solution. But my question is simply this: **How do astronauts measure mass, when they are in space, where everything is essentially weightless?** Weight is, of course, relative to gravity. But mass at rest always remains constant. I know when I was in high school, we used to measure mass, it was said, by comparing it to other masses, on a balancing scale. You can’t do that in space. Also, I do have a partial solution myself. But I don’t know if it is even feasible. Why not, _ **throw** _ something in space? Then measure its mass. When something is thrown, the impact is still the same, isn’t it? Though really, I am not even sure about this. IANAPhysicist (or scientist, even). I patiently await your replies:) ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [November 16, 2016, 4:00pm UTC](https://boards.straightdope.com/t/measuring-mass-in-weightless-space/772169/2 "2016-11-16T16:00:30Z")
F= ma. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [November 16, 2016, 4:02pm UTC](https://boards.straightdope.com/t/measuring-mass-in-weightless-space/772169/3 "2016-11-16T16:02:54Z")
Weight isn’t relative to gravity, it’s the measure of gravity … we can say such-and-such “weighs” 100 lbs, or we can say “the magnitude of the force of gravity is” 100 lbs … or even it weighs 500 Newtons … Your solution has merit … if we apply a 1 Newton force to an object and then measure the acceleration … we can use Newton’s 2nd Law of Motion … F = ma … and quickly solve for mass … for a force of 1 N, we have acceleration of 1/4 m/s/s, we know the mass is 4 kg. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [November 16, 2016, 4:14pm UTC](https://boards.straightdope.com/t/measuring-mass-in-weightless-space/772169/4 "2016-11-16T16:14:41Z")
[You asked this question four years ago.](http://boards.straightdope.com/sdmb/showthread.php?t=672256) ---
**Author:** ![Jim\_B](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jim_b/32/4338_2.png) [@Jim\_B](https://boards.straightdope.com/u/Jim_B)\ **Post date:** [November 16, 2016, 4:21pm UTC](https://boards.straightdope.com/t/measuring-mass-in-weightless-space/772169/5 "2016-11-16T16:21:02Z")
> [@Machine\_Elf](#): > > [You asked this question four years ago.](http://boards.straightdope.com/sdmb/showthread.php?t=672256) I had a vague recollection I did. You know, I am not as young as I used to be;). My memory is beginning slow, even now. I’m serious. Just two things, I will say then: (1) always check, to see if your question was asked before (I hope from now on, I will:smack:); and (2) let’s rehash the question, by all means. There are some new people on the boards, I have noticed. Let’s see what they have to say, now:). ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [November 16, 2016, 5:00pm UTC](https://boards.straightdope.com/t/measuring-mass-in-weightless-space/772169/6 "2016-11-16T17:00:28Z")
> [@John\_Mace](#): > > F= ma. Specifically, they use a body mass measurement device which acts as a single degree of freedom oscillator; on Skylab this was known as the M172 Weight Chair as detailed [in this newsletter (pg 7-9)](http://www.vibrationdata.com/Newsletters/October2001_NL.pdf) from Tom Irvine’s [Vibrationdata.com](http://Vibrationdata.com) site. On the International Space Station, a similar device known as the [Space Linear Acceleration Mass Measurement Device](http://www.nasa.gov/mission_pages/station/research/experiments/640.html) is currently used. Stranger ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [November 16, 2016, 5:17pm UTC](https://boards.straightdope.com/t/measuring-mass-in-weightless-space/772169/7 "2016-11-16T17:17:22Z")
In high school we had an inertial balance. I’d guess that use something along those lines. I don’t think gravity would come into play with that. [Here’s a video](https://www.youtube.com/watch?v=n3xjKuFEr2M). FTR, I didn’t watch or listen to it, I just looked for a video. All I really remember from HS is that you put a mass in it, and let it oscillate back and forth and counted the oscillations for a given amount of time (or a set number of oscillations and counted the time) and from there you could calculate mass.