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I'm writing a trivia quiz and intend this question, which dates from a high school physics test I took in 1972. An astronaut tips the scale at 60 kg while on earth, what will she be if she steps on the scale on the moon? Answer 60 kg. Kg measures mass, which is constant. The question is not in pounds, or ask about weight. Yes, it is a trick question, but I think it is an entertaining one. The point is, I've looked around the internet and the discussion all focus on in common usage, weight is mass and nobody knows what a Newton is. I'm certain of my answer, but I'd like to be ready for some blowback.

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    $\begingroup$ As you can see from the variety of answers, you must specify what type of measurement device your are using. Are you using a static spring scale, a strain gauge scale, or a balance scale? And it doesn't matter what units the scale specifies. It's the measurement process that's important. One could also use an oscillating spring system. $\endgroup$
    – Bill N
    Jan 21, 2020 at 4:35
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    $\begingroup$ I'm voting to close this question (v1) as off-topic because it seems to be more about a deliberately misleading trick question than physics. OP already seems to know the difference between mass and weight. Questions on SE should always be stated as clear as possible to the abilities of the asker. $\endgroup$
    – Qmechanic
    Jan 21, 2020 at 9:49

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The answer depends on the type of instrument you are allowed to use for the measurement. The two types are:

  1. Weighing Machine type

  2. Beam Balance type

    Weighing Machine

This instrument (weighing machine) measures the downward force applied by the object and then divides it by $g$. That is if your body applies a force of $W$ on the scale then the scale would show a value of $W/g$. This is because $mg=W$ on earth. But say you are on moon and the machine is celebrated for earth then the body applies applies a force say $W'$ then the reading shown by the scale would be $W'/g$. Now on moon $a=g/6$. Therefore the scale would show a reading of about $m/6$ i.e., this machine on moon measures $10kg$ for a body of $60kg$ on earth.

Beam Balance

This instrument (beam balance) works on the principal of moments and therefore for equal arm length it measures the mass of the body. So if you are using this instrument then the value would be same wethere you are on moon or earth.

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Unfortunately, scales do not measure mass. They measure the force applied by the mass, under the influence of the local gravity. The fact that they are labelled in "mass" is irrelevant. All that happens is that the readout is "adjusted", so that 588 N is shown as 60 kg.

Hence, on the moon your scales will show about 10 kg.

EDIT

I disagree with the comments: even if you are using balance scales, you are measuring force, not mass. Consider the following 2 graphics enter image description here

enter image description here The first shows a normal balance, the second an unequal-arm balance. In the second image, it makes no sense to say that 30 kg balances 60 kg. The balance is achieved by having equal torque (moment of rotation) on both sides. Torque is given by $\tau=r\times F$ where $F$ is force, not mass. Hence balance is achieved by using forces of 588 N and 294 N.

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    $\begingroup$ A balance scale measures mass. (It balances the weight of one mass against the weight of another.) A spring scale measures weight. $\endgroup$
    – G. Smith
    Jan 21, 2020 at 2:44
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    $\begingroup$ aAs was just pointed out,: A balance scale measures mass; a spring scale measures force. The phrase "tips the scale" seems to imply a balance scale... $\endgroup$
    – DJohnM
    Jan 21, 2020 at 2:46
  • $\begingroup$ The original question never mentioned balance scales, but I assume I should have mentioned them - or waited for the edits. $\endgroup$
    – hdhondt
    Jan 22, 2020 at 22:10

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