Conceptually I understand that mass is a measure of the amount of stuff present in an object, while weight is a measure of the force of gravity applied to that object. An object of a given mass will have a bigger weight on Earth than on the moon because Earth’s gravity is stronger. But… mass is determined by weighing an object on a scale. And there is a simple mathematical conversion between grams (mass) and pounds (weight), implying that they’re just different units for the same concept. So what gives? (Also this is a question that applies to so many fields, I had no idea which flair to apply.)
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The difference of these two concepts became apparent to science in the 17th century with the Newton laws. Although he knew the conceptual difference, he used the same word as weight for mass too, as there were no terms coined yet.
In the everyday life it’s a very hard to grasp difference, because you cannot just grab your bathroom scale and check your weight on the moon, and in general, things that have more material naturally have more weight with some weird exception.
Because the imperial system was invented before the distinction was made (and anyways it’s fir everyday use), US people don’t even have different units for weight and mass so they take kilograms from the metric system. Which makes it feel not integral part of the system. (Also in the US there’s this thing called mass-pound (lbm), to cause some more confusion.)
In Europe the bathroom scales and in general the weights of stuff are given in grams or kilograms so basically in mass units. I have my cooking recipes in kilograms. Weight unit in the metric system is called newton but it’s not used in the everyday life. (It’s newton because weight is defined as the downward force an object exerts on the support, and force unit in metric system is newton.)
But in fact European scales cheat because although they tell the results in kilograms, they do not measure mass. They measure in fact the change of electric current due to deformation of a thin wire inside, which is proportional to force. So they measure force but give the result in mass.
Mass is how much stuff you’re made of.
Weight is how hard the earth’s gravity pulls down on your mass.
Bonus: Density is how close the stuff you’re made of is together.
If I took a 4in cube of iron and weighed it, then smushed that block so it was only a 1in cube (increasing the density) it would weigh the same, but still have the same mass.
Edit: I’m dumb and didn’t read the rest of the post.
>But… mass is determined by weighing an object on a scale.
This is where you’re wrong. Yes, in the presence of a known gravitational field (i.e., on Earth), you can weigh an object on a properly calibrated scale to figure out its mass. But what if you were in outer space? A scale would tell you that you’ve got zero mass, which isn’t true. Or what if you were on Pluto, and you didn’t know Pluto’s gravitational force offhand, and you were fresh out of Pluto-calibrated scales? An Earth-calibrated scale would be useless to figuring out your mass here.
Instead, think of mass as a measure of how hard it is to move something, or change something’s momentum. If I’m standing (floating) still in a spaceship in outer space and you throw a 7 kg bowling ball at me and I catch it, I’m going to start moving backwards at a particular speed. That speed will be slower if I have a high mass, and faster if I have a slow mass. Even though a scale is useless here, I could still calculate my mass using this kind of method (and many other methods). But a scale would show that my weight is zero.
F = m•a
m = F/a
If I apply a force of 100 N on an object, and as a result it accelerates at 5 m/s^2, then I know it’s mass is 20 kg.
Mass is the quantity of matter. How much stuff is there. Weight is the force of gravity acting on that mass.
Scales that provide a mass result only work in the special case of roughly 1g. Otherwise it will need to be recalibrated human experience has been mostly confined to our 1G working environment and so this has not proven to be an manageable problem thus far.
Mass is how much stuff something is made up of. Weight is how gravity affects that mass in proportion to the gravity it is being effected by. So say something is made of a bunch of atoms or particles or whatever, that’s the mass. How much that object weighs depends on local gravity’s affect on that mass. The object will always have the same mass whether it’s in space or on earth, but the gravity around it will change the “local” weight of the object.
Mass is *not* measured by weighing it on a scale. Mass is measured with a “balance”. That means it is measured against some item of known mass. The balance checks to see how much of the known item it takes to counteract the effect of gravity on the thing you’re measuring.
Since it’s two items being compared, we know gravity will affect each of them the same if there is the same amount of stuff in each one, so the actual strength of gravity doesn’t matter.
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