Have you ever picked up something that looks really heavy only to find out that it is really light? This obviously makes you looked like a fool in front of your friends but try to style it out into a fancy dance move (it totally worked BTW). Well, this is the concept of density in action – and (amazingly) the topic of this activity. You will be defining density and explaining how to measure it experimentally by the end of this activity – like a boss!
So – density is a measurement of the mass of each particle AND how many of those particles there are in that object. If you have a lot of heavy particles in 1 cm3 then you will have a high density, but if you have only a few light particles in 1 cm3 then you will have a low density.
The easiest way of picturing this is by looking at the solid, liquid and gas particles models.
In a solid, the particles are close together in a regular lattice. They are vibrating all over the place, but they tend to stay in their one specific spot. This makes solids denser because there are a lot of particles in a small area. What do you think about liquids and gases then?
In liquids, the particles are all touching still but they are free to flow over each other. This can lead to small gaps forming in their shapes and that means that you can’t fit as many particles in the same space. This means that the density is slightly less than a solid – this is why water is so heavy because it has a high density.
In a gas, the particles are free to go wherever they want (they are freeeeee). They tend to move quickly and have large gaps between the particles. This means that they have a low density because the particles are far apart.
So that is an overview of density – now how about we look at how to measure density in a lab. This is a common question, so you need to remember this method of measuring density. Let's start off by thinking about how you would measure density? Well, we know it is the mass of the particles and how many there are in an area. This means that we need to use a divide – what do you think it should be?
This is the equation:
That funny sign (ρ) is the Greek letter Rho, in this case, it means density. Density is measured in kilograms per meters squared (kg/m2), m is mass and is measured in kilograms (kg) and V is volume, measured in meters squared (m2).
So now how do we work it out in a lab? Let’s say you have a block of wood and you want to work out its density. By looking at the equation, we know that in order to work out its density, we have to know its mass and its volume.
Working out the mass is simple; you just need to put it on a top pan balance and read off the measurement that it gives you (making sure that you zero the balance to start off with).
The volume isn’t all that difficult, all you need to do is measure the length, width, and depth of the object. You then multiply these numbers together and you get your volume.
DO EQUATION HERE
You can see from this image that our mass is INSERT MASS and our volume is INSERT VOLUME
So, our density is:
DON’T FORGET the units! Always put them in unless the question tells you otherwise!
And that’s it! Now you are a master of density! Let’s put your newfound knowledge to the test!