The difference is gravity. Weight is dependent on gravity while mass isn’t. So if you had a 5 kg object and you brought it to space, the weight would be 0 but the mass would be the same.
Grams are a measure of mass, not weight. If you’re being pedantic, newtons would be the measure of weight in the metric system, but since the vast majority of us only have to deal with Earth’s gravity, we use mass and weight interchangeably.
Mass is how much ‘stuff’ you have in a thing. Weight is how heavy it feels in gravity.
That’s why you would weight differently on different planets.
So your mass isn’t changing, you’re still made of the same stuff…. but your weight changes because bigger planets will pull on you harder than smaller planets…. so you weight more on large planets than you do on smaller planets, but you have the same mass.
Weight is gravity acting on mass. Mass is (very roughly) how much substance the object has whether or not it happens to be subject to any significant gravity at the time.
Because the vast majority of us only ever worry about earth gravity and don’t experience any other circumstance people generally use mass and weight interchangeably, but they aren’t exactly the same.
For example: lifting someone on the moon would be easier. That’s because they weigh less on the moon because the moon has less gravity. If they tackle you on the moon, though, they’re still going to hit just as hard because they have the same mass which carries the same kinetic energy at a given speed. None of their substance vanished by the change in gravity, there is just less gravity to act on it.
You go into a region of space where there is almost no gravity, you will have no weight. If you tried to stand on a scale, it would read zero.
You still have just as much mass as you did before, but now that gravity is gone you have no weight because there’s no gravity pulling that mass down.
If you went to some massive planet with strong gravity, you’d feel waaaay heavier, but your mass wouldn’t change.
What a scale does is measure your weight – the force of gravity pulling you down. Because we are all on Earth, you can calculate your mass based on your weight. A scale can therefore measure both at the same time. However, grams are *technically* a measure of mass.
Mass is measured in grams, and for everyday things so is weight, but wieght’s official unit is actually newtons (N). We use grams instead of newtons because before Newton the difference between weight and mass didn’t really “exist” as the *concept* of inertia didn’t exist, and we have just kinda stuck with it.
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