Stoopid basic physics question / just checking (rusty brain).

it's MASS though, isn't it? It's weight would be 1,600 kg x g = 1,600 x 9.81 =

So it's its weight and its mass... weight is not measured in newtons..

Its mass is 1600kg. Its weight varies according to where you are (e.g. slightly less at altitude, and a lot less on the Moon).

it's MASS though, isn't it? It's weight would be 1,600 kg x g = 1,600 x 9.81 =

Assuming you live on Earth, its weight is, for most practical purposes,

Colin Bignell

Weight and mass are different. Strictly speaking weight IS measured in newtons. What we've got here is the difference between the scientific definition and everyday parlance.

Biggles

I'm sure weight was indeed measured in Newtons when I was at school.

David

I'm curious why this in fact matters?

Brian

Well, I never did quite understand this myself. The most useful measurement is the weight, ie if you put it on some scales. The mass of that matters of course when you look at what it takes to move and stop it, however the aire resitance is also important, and that changes with speed and is very complex indeed. Brian

It's becaus'e you're suffering from grocer's' apos'trophe s'yndrome.

Only if you use the bathroom scales type of scales, i.e. with a spring. Then you're measuring how much *gravity* pulls the item down, and it will show much less on the Moon.

If you "weigh" it with a balance, you're actually measuring mass, and you'll get the same result on Earth and Moon.

All but the most pedantic scientists would accept weight 1,600 kg(f) with or without the f for force. There is no ambiguity in common usage. Chances are very good that it was measured as a weight on *Earth*.

The same sort of people that obsess about these things also go on about US vs UK billions (despite the fact we adopted US usage in 1974).

None of this adds anything to understanding of the physics.

There is a fairly strict difference in metrology in that weight is measured by for example by the extension of a calibrated spring balance or strain gauge whereas mass is measured by matching a combination of reference weights on one scale pan to the unknown mass. This latter measurement would give the same answer if done on the Moon or Jupiter.

It is a source of some embarrassment to physicists that whereas the SI units of time and length are precisely defined in terms of universal constants of nature the fundamental SI unit of mass is still a reference lump of platinum in Paris that is slowly deteriorating.

Same problem arises with blood pressures as mmHg in hospitals. They tried converting to Pascals and ended up with meaningless charts where the patients would mostly be dead because of scaling errors made when converting between the familiar old units and the new. They gave up.

The UK public conversion from Fahrenheit to Centigrade/Celsius was a notable success for the metric system. Metres and kg less so. We still have speed limits in mph but petrol sold by the litre. I find miles per litre a very handy hybrid unit amenable to mental arithmetic.

That reminds me of a physics question at school in the late 60s in which NASA did that experiment and did *not* get the same result. The answer was that one of the items had an evacuated void - to be tested by putting the balance in a vacuum chamber on Earth.

Of course in the question NASA weren't weighing cars :)

That's it's MASS though, isn't it? It's weight would be 1,600 kg x g =3D 1,=

MBQ

So, how much did Newton weigh?

I am sure he weighed lots and lots, all that mercury and other alchemical stuff - maybe his notebooks tell us? :-)

I have a vague memory of "poundals"

No that would be mass, (if they were proper balancing scales), put it on a spring scale if you want weight.

The mass of that matters of

New Scientist pointed out a while ago that, each time they do the periodic cleaning of the Reference Kilogram, the mass of every other object in the universe increases instantaneously.

well force is measured in newtons, so you weren't measuring the weight, you were measuring the force exerted by the weight.

Which is why the unit kilogram force exists, which is the force creeted by a mass of one kilogram in standard 1g gravity.

Weight as such is not a property that exists in Newtonian physics. F=ma and nowhere in there is weight mentioned.

Weight is a convenient way for non scientists to talk about mass, thats all.