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  • Weighing machines: what do they read ?

    zaveri

    Member

    Updated: Oct 23, 2024
    Views: 1.7K
    Mass and weight may sound the same thing, but they aren't. while mass is a scalar, which only is the quantity of substance in a body, weight is actually a vector quantity.

    in fact wight is another form of force. it is a force which always acts downwards,(on the negative side of the y axis).

    the equation of force and weight are also similar, F=ma for force, while W=mg for weight.

    this means that weight and mass can never be mistaken to be the same thing, since the equations show that mass is actually a factor of weight.

    similarly both these quantities also have different units, (kg for mass and N for weight).

    but nowadays according to the layman's language, weight actually means mass.

    so now this leads to a confusion as to the units of the readings of the electronic scales.

    when the electronic scale reads a value, its units are kg or newton. ?

    can the reading so obtained be directly assumed to be in newtons and used as data for solving problems in strength of materials , etc.
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  • Ramani Aswath

    Member • Jul 18, 2012

    The old two pan balance just compares two weights. Since the staandard weight and the unknown weight are seeing the same gravitational force, the reading will be the same wherever (including on the moon or elsewhere) the weighing is done.
    The sensors in an electronic balance respond to stressses, hence weight. An electronic scale on the moon will show about 1/6 the value on earth. Even on the earth itself the ploles will show a small increase in the value compared to the equator.
    Having said that, for all practical purposes we can use the values interchangeably. Units must however be conserved.
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  • zaveri

    Member • Jul 20, 2012

    bioramani
    The old two pan balance just compares two weights. Since the staandard weight and the unknown weight are seeing the same gravitational force, the reading will be the same wherever (including on the moon or elsewhere) the weighing is done.
    The sensors in an electronic balance respond to stressses, hence weight. An electronic scale on the moon will show about 1/6 the value on earth. Even on the earth itself the ploles will show a small increase in the value compared to the equator.
    Having said that, for all practical purposes we can use the values interchangeably. Units must however be conserved.
    so what do you mean to say in the end ?
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  • Anil Jain

    Member • Jul 20, 2012

    Take anything to any machine (in practical life, don't go to lab to prove me wrong 😁 ) Any machine would be measuring only weight.

    Even you are using the two pan balance, it also measures the weight; the only difference is their would be weight on both the side which has the equal gravity applied so while measurement we can cancel that out. and can get the mass (just a way to find it).

    To prove this, we can find out mass from the two pan balance (may be 1 Kg mass), and then measure the same mass on a electronic scale (rather I would say maniacal weighing machine, as electronic machine may still show the correct answer after eliminating the gravity value), should it show reading more than 1kg preciously, as it has a gravity including as well.

    Answer is - Yes it should.

    Do you agree?
    Correct me if anyone disagrees.

    -CB
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  • zaveri

    Member • Jul 20, 2012

    crazyboy
    Take anything to any machine (in practical life, don't go to lab to prove me wrong 😁 ) Any machine would be measuring only weight.

    Even you are using the two pan balance, it also measures the weight; the only difference is their would be weight on both the side which has the equal gravity applied so while measurement we can cancel that out. and can get the mass (just a way to find it).

    To prove this, we can find out mass from the two pan balance (may be 1 Kg mass), and then measure the same mass on a electronic scale (rather I would say maniacal weighing machine, as electronic machine may still show the correct answer after eliminating the gravity value), should it show reading more than 1kg preciously, as it has a gravity including as well.

    Answer is - Yes it should.

    Do you agree?
    Correct me if anyone disagrees.

    -CB
    your method seems practical. put a 1 kg mass on an electronic scale, if the reading shows "one", then it reads mass, but if it reads 9.81, or some value in that range, then it is reading weight in Newtons.
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  • Ramani Aswath

    Member • Jul 20, 2012

    crazyboy
    To prove this, we can find out mass from the two pan balance (may be 1 Kg mass), and then measure the same mass on a electronic scale (rather I would say maniacal weighing machine, as electronic machine may still show the correct answer after eliminating the gravity value), should it show reading more than 1kg preciously, as it has a gravity including as well.-CB
    If you have a two pan balance and an electronic balance on the moon the two pan balance will still show 1 kg, while the electronic balance will show about 150 gms.
    Anywhere on earth there will not be much difference.
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  • Anil Jain

    Member • Jul 20, 2012

    bioramani
    If you have a two pan balance and an electronic balance on the moon the two pan balance will still show 1 kg, while the electronic balance will show about 150 gms.
    Anywhere on earth there will not be much difference.

    I agree sire !
    The whole point I was trying to put is two pan balance is doing an comparison; however electronic balance is showing you weight that's why it will be 1Kg here and 150 gm at moon.

    On the contrary I can say, when you are saying that two pan balance would still show 1kg on moon; you are assuming that the slandered weight is of 1 Kg was on earth not on moon, because on moon it should have been 6 KG, right?

    The whole point I want to mention here is it is very tough to measure Mass; practically we always measure weight; do you agree?

    -CB
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  • Ramani Aswath

    Member • Jul 20, 2012

    Not quite. The mass is invariant wherever it is , even in zero gravity. As you said the two pan balance is a comparator. All it says is that this mass is equal to that. It will be in trouble in zero gravity though, as that is equivalent to multiplying by zero which makes everything zero. One possibility is to use inertia. The force required to accelerate a mass is specific to the mass.
    Quote:the standard weight is of 1 Kg was on earth not on moon, because on moon it should have been 6 KG, right? Endquote

    Two pan balances use mass standards, so the mass shown on moon will be 1 kg but the weight will be 150 gms.
    Let us look at it this way. For the moment we ignore density differences due to ambient. If we weigh 1 litre of water on earth and moon it will show 1 Kg on a two pan balance, but a weight of 1 Kg here and 150 gms on the moon.
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