Hi guys. I know that mass is the amount of matter in an object and weight is the pull of gravity on an object but here's what I don't understand. How can grams be used to measure mass? Let's say an object is 200 grams - which would be like 200 paper clips, right? Would the object still be 200 grams in space? Doesn't a gram measure weight, not mass? So confused. And how can we effectively teach the difference between the two when all students' experiences are grounded on Earth, where the terms weight and mass can be used interchangeably?
The paper clip would remain 200 grams. Grams do not measure weight, but because of common usage, we tend to say "weigh the mass of". The correct verb would be, "I need to find the mass of this." In addition, a mass scale isn't the same as a weight scale. A mass scale takes the weight of an object, corrects for the gravitational constant, and provides the mass. The best way to teach it I think would be to compare the weight of a person when on different planets, i.e. the moon, or Jupiter, etc. The person would remain the same mass (i.e., they're made up of the same parts, but because of the gravity of the planet, their weight would be different). Tell students that when people are trying to lose weight, they are technically trying to lose mass. =]
Think of measuring mass on one of those balances with two pans. You put the paper clips on one side and a 200g weight on the other side, and it balances. It would still balance if you did this on the moon. If you step on a scale on the moon, though, you won't weigh as much because gravity isn't pulling you down as much.
When I taught physics I would make my students calculate their weight on different planets and the moon so they could see how gravity affects it. Because their mass was always the same but the weight changed.
I think I'm starting to get it. So let's say you use snap cubes instead. If an object is balanced by 20 snap cubes on Earth, it should also be balanced by 20 snap cubes in space, right?
Well, assuming that both the snap cubes and the item would stay in the balance pans, yes. They'd certainly balance on the moon. What's more, this is why a proper scientific scale is a balance scale: since gravity is acting on both sides of the scale, it factors out.
