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I Have read an earlier post regarding this, but the answer wasn't perfect enough or I didn't understand so!

Let me put it to clear, I know difference between weight and mass. Also I know the conventional method of denoting "Kg" and "Kgf" as units of weight in some countries.

My question is, say for example of a car. It is said that Toyota corolla has a curb weight of 2800 pounds or 1270 Kg. Does the above spec actually denote the weight(mass x g) or mass of the car?

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    $\begingroup$ The difference is pretty pedantic. No doubt the car wasn't measured on a mass balance but instead the force of gravity on the car was measured and then gravity factored out to estimate the mass. $\endgroup$ – Brandon Enright Jan 9 '14 at 8:46
  • $\begingroup$ can you link the earlier post, so we can understand better what you're missing? Also, answer is mass, not weight. $\endgroup$ – mart Jan 9 '14 at 8:46
  • $\begingroup$ I am sorry, but I found the post in another site, physics forum, physicsforums.com/showthread.php?t=215885 so mart, I guess u mean the car I just mentioned has a total weight of 1270*9.81 N..right? $\endgroup$ – Roopesh Jan 9 '14 at 8:48
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In 99% of the cases, when you say weight, you mean mass.

It's supposed that weight is the force of gravity experienced, so a reasonable unit would be the Newton.

This means that $9,8 \mathrm{N}=1\mathrm{kgf}$. So, to be consistent with this definition, the Toyota weights $1270\mathrm{kgf}$.

But I don't know any case where the difference is important.

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  • $\begingroup$ When we say weight changes at different altitutes ,does we say mass changes? $\endgroup$ – user31782 Jan 9 '14 at 13:42
  • $\begingroup$ @anupam No, because mass is constant, weight is not. $\endgroup$ – jinawee Jan 9 '14 at 14:17
  • $\begingroup$ Can you cite any of the 1% remaining cases. $\endgroup$ – user31782 Jan 9 '14 at 14:34
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    $\begingroup$ @anupam High school physics where they ask you to tell the difference between both and when people say things like "in the Moon you weight less". There may be other cases which I don't know, like engineering. $\endgroup$ – jinawee Jan 9 '14 at 15:39
  • $\begingroup$ I've forgot an important case, when you analise the forces of an object, like a pendulum, you consider weight as a force. $\endgroup$ – jinawee Jan 9 '14 at 15:53
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Weight in physics is the Force applied by earth on an object given by $F=mg$ where $g=GM/r^2$. But in colloquial language wieght is approximately the mass of that object. Usually 1 Kg in colloquial and in trading of goods represents 1Kgf=9.8 N force.
It is technically different from the actual mass of an object. The difference is that the mass remains always constant but not the weight. Except the weighing scale(Balance) every other equipment( like spring scale or a digital electronic scale) shows different readings of weight of a given object at different altitudes.
When we say a car say Maruti has a weight 650Kg it is approximately its mass. Precisely Measured weight= (Force of gravity)/ 9.80665 which is approximately equal to the actual mass.

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