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Simple question

  • 02-02-2010 8:38pm
    #1
    jumpguy
    Registered Users, Registered Users 2 Posts: 7,962 ✭✭✭


    I've been wondering this for the last while, but if you were in a laboratory with no gravity, and you have an object of unknown density? How would you measure the mass? You can't set it on a scales, is there a way you could possibly measure density (without d = m/v, since mass isn't known)?


Comments

  • #2
    [Deleted User]
    Posts: 4,630 ✭✭✭ [Deleted User]


    If you could accelerate the body you could determine the body's inertia, and a body's inertia is directly proportional to its mass. So, quick answer, just measure acceleration.


  • #3
    jumpguy
    Registered Users, Registered Users 2 Posts: 7,962 ✭✭✭jumpguy


    -JammyDodger- wrote: »
    If you could accelerate the body you could determine the body's inertia, and a body's inertia is directly proportional to its mass. So, quick answer, just measure acceleration.
    Ah yes, never thought of that! Is that F=ma you mean?


  • #4
    [Deleted User]
    Posts: 4,630 ✭✭✭ [Deleted User]


    Yah, that's the idea, or some variation of that equation.

    I googled it and there's a good response to this question here.


  • #5
    Bodicea
    Registered Users, Registered Users 2 Posts: 41 ✭Bodicea


    -JammyDodger- wrote: »
    Yah, that's the idea, or some variation of that equation.

    I googled it and there's a good response to this question here.

    I was just going to suggest throwing something of known mass at it and calculating from that.:D


  • #6
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 93,563 Mod ✭✭✭✭Capt'n Midnight


    Bodicea wrote: »
    I was just going to suggest throwing something of known mass at it and calculating from that.:D
    that would work , you could probably measure the angle of deflection more easily than a whirling scales

    spining to get a g-force is problematic since the weight depends on the radius and in current spacecraft you are unlikely to get more than a few meters to swing the cat in so to speak and most things you want to weigh would be in the order of centimeters in size so the acceleration at one part of the object would be different to another part, getting three digits of accuracy would be difficult

    in the old days they used to measure electrical current with a current balance , using weighing scales. Reversing it you could compare current with acceleration to you a far more accurate reading

    An Ampere is defined as the amount of current that will produce an attractive force of 2 × 10–7 newtons per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum.

    If all else fails you can of course measure the current by the volume of gas electrolysised by it.


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