Measurement

[lacyfischer]

what is the tool used to measure mass

[heathfield]

Mass is a measure of how heavy something is. Weighing scales are the tool used.

[vascop]

This is not really correct, as the same mass would be a different weight on the Moon say. However if you stay on the same planet then you can compare masses by using the weight. So if something is twice as heavy as something else then its mass is also double.
Weight is the measure of the force of gravity on a body, whereas mass is just the amount of matter in the body.
However Heathfield is right about using scales - as long as you stay on the same planet while you do your measuring.
You can't compare masses you have measured on the Moon using scales with masses you've measured on earth using scales. You would need to know how much weaker gravity is on the Moon to able to compare them. If say the moon's gravity is a sixth of the earth's then everything on the Moon would weigh a sixth as much on earth.
If a Moon buggy robot does an experiment on the Moon involving mass and using scales, then this fact would have to be taken into account.

[factor-fiction]

Strictly correct vascop.
Next time I am asked what my weight is I'll ask them whether they mean when I'm on earth or on the moon.
I suppose it depends on the reason lacyfischer asked. For GCSE and below weighing scales would be an acceptable answer , eg http://www.bbc.co.uk/schools/ks2bitesize/maths /revision_bites/measures2.shtml

[wildwood]

Wouldn't balance scales work the same on Earth as on the moon?
If they do, I'm sure that's what heathfield meant.

[Symmetryigr8]

A classic pair of "libra" scales will work anywhere as they just compare the masses of the two sides. But if two objects balance the scales in one place then they will always balance assuming the gravitational field is constant for both sides which it should always be.

[vascop]

Yes if you use 'Libra' type scales you would be OK, otherwise you would need to re-calibrate your scales on the Moon.

[vascop]

When I say 'on the Moon', I mean for use on the Moon, not do the calibration on the Moon!

[Maypole]

Mass is the only unit of measurement still defined by a physical object - a standard kilo. In the UK the mass measuring gurus are at the National Physical Laboratory. From their pristine kilo they calibrate scalesat the National Weights and Measures Laboratory which is then filtered down to all of us with all of our calibrated scales in companies, universities etc

http://www.npl.co.uk/server.php?show=nav.394

[heathfield]

Well you wouldn't have to go to the moon. An object's weight will differ depending on where it's situated on Earth. It'll weigh less on a mountain top than at sea level, and will weigh less at the Equator than it will at either of the poles.

Which begs the question... do the French and British standard kilos weigh the same, since they are separated by some degrees of latitude? Hmmm.

[wildwood]

And afaik it doesn't need to be a 'libra' type scales either. Any scales that utilises counterweights such as this should work equally well on the Moon (or a mountain top :-)

[vascop]

The point is though, that mass and weight are two completely different concepts in physics.
Weight is a force and mass is not.

[Bert]

What people mean when they talk about the weight (of a given mass) being different on the Moon, lacyfischer, is the weight when determined by something like a set of bathroom scales, i.e. anything which determines the mass of a body by actually measuring its weight, i.e. by directly measuring the force of gravity on it. There was a type of weighing machine brought out in the 1970s that determined MASS by finding the change in the frequency of vibration of a spring when the mass to be determined was attached to it. This is independent of gravity. It didn�t catch on, however. The London kilogramme was compared with the Paris kilogramme in Paris, heathfield, as were all the other International Standards of mass.