Video transcription

Hi. I'm Steve Jones and I'm going to tell you how to calculate density. Well I'm going to tell you a little bit about how to calculate density and also how to measure density. The two things are linked. So first of all, by definition, density is mass divided by volume. Density tells you how heavy the same amount of stuff is. You know that iron is much heavier than water and wood and things like that. And of course you say lead is very heavy. Well lead is very dense. Of course you can have a small amount of lead which is heavier, sorry, lighter than the same amount of feathers or a larger amount of feathers. So let's have a look at the density. Mass is measured in units of grams and kilograms. Volume is measured in units of centimeters square or cubed or meters cubed. Right. So here is an example. We have a cube one centimeter by one centimeter by one centimeter. Piece of cubic material. Actually this probably something like steel or iron or copper. The mass was measured on a balance. The balance of this kind where you have two pounds, one on each side. That measures mass. And you put your cube on this side and you put your masses, your standard masses on the other side. So this is a mass measuring machine. The mass turned out to be eight grams. The volume is one cubic centimeter. So the density, if I write it here, the density is just the mass over volume. The mass is eight grams over the volume which is one and that equals eight grams per centimeter cubed. Remember the units. If we had done this in meters and measured the mass in kilograms, we would have gotten a result a thousand kilograms per cubic meter. But you wouldn't have been able to lift the cube. Sometimes the masses are not nice even shapes and if they're not, you can lower them into water to measure their volume. Measuring the mass is not difficult. You just put it on a scale. But to measure the volume, you should immerse it in water and what will happen as you lower it in, the water level will rise. You can measure the difference in volume and you can calculate mass over volume and that will give you your density. So that briefly is how to calculate density.