Mass explanation: I’ve always been told that mass was not the same as weight, and that grams are the metric unit of mass. But grams are a measurement of weight, so am I stupid, was it was explained to me wrong, or is science just not make sense?
In: 140
So your question is about words, as much as it is about science. In this case, it’s about two things that mean the same thing in one particular case, but they are very different things.
Mass is an amount of ‘stuff’.
Weight is the *force* that ‘stuff’ does to something else.
I have a mass of 100 kilograms. When I stand on a scale at home, I put 220 pounds of force on that scale. If I’m in space, I have a mass of 100 kilograms. But I step on the scale, and I am ‘weightless’.
If I step on a tree branch, then I am using 100 kg, in order to put 220 pounds of force on the tree branch. But I can also take a hammer that weighs 2 kg, and swing it really hard, and put 220 pounds of force on that tree branch.
This actually came up yesterday.
Here is a slightly editted version of my answer from yesterda.
–
In physics:
* Mass is basically how much matter something contains. (Its not exactly that but it is kinda like that.)
* Weight is the force of gravity on that mass. Technically measured in Newtons, (but you can measure it in ‘how much mass would you need to generate this force near the surface of the Earth from its weight’.)
* The weight measurement on a scale is the force needed to hold up the object being measured.
In common, everyday language and scenarios, if you are near the surface of the Earth, and neither you nor the scales are accelerating, then those 3 things are essentially all the same, because they are designed to try to measure the same thing. We calibrate the scale to not show ‘Newtons’, but instead show ‘the amount of mass needed to produce a weight force of this magnitude’.
So if you put a 1kg mass on a scales, then a weight force pressed down on the scales. A physicist would measure the force in Newton’s, but for our every-day use, the readout is calibrated to say “This is as heavy as a stationary object with a mass of 1kg near the surface of the Earth would be.” (which, since you *are* near the surface of the Earth, means that it *is* 1kg of mass).
(If you happen to be not near the surface of the Earth, or and using scales that are accelearating, then these 3 concepts can become separate, and you probably need physics calculations to be able to use them in any useful way. Your scales will display the wrong mass on the Moon, or in an elevator, for instance.)
Assume the universe existed of only balls (the kind that you play sports with, not the ones that all men normally have).
Assume all balls were exactly the same size. Since the universe is made out of balls, you can assume the material the balls are made of “themselves”, so it’s not like one ball is any different than another in terms of material or density and such.
Anyway, mass is basically a count of how many balls something is made of. If I make a statue out of balls, regardless of where I am (underwater, on Mars, on earth, on the moon), the statue is made up of the same number of balls.
Weight is how hard will the statue crush me? In space, it’ll weigh nothing. Because it can’t crush me at all. I guess I’m missing a technicality – weight is how much can something crush me while it’s not moving, but is being attracted towards something when not moving. This is needed to be specified, because if I jump, I’m technically a negative weight by this logic, and when I’m falling back down from the jump, I actually end up weighing more (which is why you might not break a table if you stand on it, but likely will if you jump).
The reason we can swap weight and mass often (“2.2 lbs = 1 kg”) is because how hard you can crush something when at rest is the same all over earth for the most part. You get a little lighter if you’re on a mountain, but not enough to be noticable.
But yeah, if you’re not on earth anymore, 2.2 lbs is no longer 1 kg. You’ll still be whatever kg you were, but you won’t be the same lbs. This is because 1 kg will weigh less on the moon, and so will you. But if you were 100 kg on earth, then you’ll be 100 kg on a tiny planet. But that 100 kg may suddenly weigh 30 lbs. And in that case, you’ll be 30 lbs (but still 100 kg).
The 2.2 is missing a “*on earth” disclaimer.
So back to balls. Your statue is still the same number of balls (kg). But the weight (how hard the balls are pressing down) will change depending on how large the planet/object you’re standing on is.
Mass is like “how many atoms are in this object ?”
It will never change, no matter where you are in the universe.
Weight is like “how does gravity affect the force of the atoms in this object ?”
It will change depending on where you are in the universe because there are different amounts of gravity in different places.
Latest Answers