# Undersatinding Density

In this worksheet, students will look at the equation for density and understand how to measure density.

### QUESTION 1 of 10

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:

DO EQUATION

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!

Select the correct definition for density from the list given below.

The number of particles in a given space

The mass of all of the aprticels in an object

The amount of space an object takes up

The amount of mass per unit area

Which of these states of matter has the highest density?

Soild

Liquid

Gas

Match the symbol to the unit for the density equation.

## Column B

Density (ρ)
kilogrammes (kg)
Volume (V)
kilogrammes per meter cubed (kg/m3)
Mass (m)
meters cubed (m3)

An object has a mass of 0.1 kg and a volume of 0.4 m3. Calculate the density of the object.

An object has an original density of 1 kg/m3 and is then heated. Its new volume after heating is 0.8 m3. Calculate the change in density of the object.

Object mass = 2 kg.

What happens to the density of an object when you cool it?

It increases

It decreases

Nothing

An object is heated. Describe  and explain what happens to its density by talking about the particles (3 marks)

Describe how to calculate the volume of a cube (2 marks).

Calculate the density of this cube.

Mass of the object = 0.1 kg

Put these objects into an order of most dense at the bottom to least dense at the top.

## Column B

Least dense
Aluminium
In the middle
Ethanol (alcolhol)
Most dense
Oxygen
• Question 1

Select the correct definition for density from the list given below.

The amount of mass per unit area
EDDIE SAYS
This is one of those definitions that you need to remember - you'll find there are a lot of these in science (it's like learning a new language!). These are important, because in science when we say things we are very specific about what we mean. So if a question asks you about density, then it is asking you about this and only this.
• Question 2

Which of these states of matter has the highest density?

Soild
EDDIE SAYS
The particles in a solid are tightly packed together in a regular lattice. This means that there are a lot of them in a small space. When something is dense, there are a lot of particles in a small space - so this definitely applies to solids. Their regular shape means that they literally cannot fit any more particles in!
• Question 3

Match the symbol to the unit for the density equation.

## Column B

Density (ρ)
kilogrammes per meter cubed (kg/m...
Volume (V)
meters cubed (m3)
Mass (m)
kilogrammes (kg)
EDDIE SAYS
You don't really need to remember the symbols (especially Rho (ρ)) but you do need to be able to match the words to their symbols. This will make it easier for you to find the information needed in an exam question making it easier to answer the exam question. Everyone likes tricks that make answering the question easier, right?! So learn to match them together and you'll be well away!
• Question 4

An object has a mass of 0.1 kg and a volume of 0.4 m3. Calculate the density of the object.

0.25
EDDIE SAYS
This is a simple one if you are able to pick out the numbers and put them into the equation (which is what will be asked of you 90% of the time in the exam!). Let's go through it together: Step 1 - identify the numbers and write them down. ρ = ? m = 0.1 kg v = 0.4 m3 Step 2 - put them into the equation ρ = 0.1/0.4 Step 3 - put this into the calculator and write down your answer. ρ = 0.25 kg/m3
• Question 5

An object has an original density of 1 kg/m3 and is then heated. Its new volume after heating is 0.8 m3. Calculate the change in density of the object.

Object mass = 2 kg.

1.5
EDDIE SAYS
This one is a little more complicated because it has 2 parts to it. The first part is the simple 'work out the density' part, but then it turns into a 'work out the difference between these two parts' question. Let's have a look at how we would tackle this type of question. Step 1 - work out the density A - find the numbers and write them down: ρ = ? m = 2 kg V = 0.8 m3 B - put them into the equation: ρ = 2/0.8 C - do the maths ρ = 2.5 kg/m3 Step 2 - Now take this new value for density away from the original value of density. 2.5 - 1 = 1.5 kg/m3 DONE! Amazing :)
• Question 6

What happens to the density of an object when you cool it?

It increases
EDDIE SAYS
When you cool an object, what you are doing is stopping the particles from vibrating as much - this is what heat is, how much particles are vibrating. If the particles are vibrating less, they are taking up less space, this means that the volume of the whole object is going to go down. If you have the same mass in a smaller volume, then your density is going to go up. The correct answer here is increases.
• Question 7

An object is heated. Describe  and explain what happens to its density by talking about the particles (3 marks)

EDDIE SAYS
This question has an 'explain' in it - this means you need to have a BECAUSE in your answer. In this question, you needed to use the 'because' in the part where you were linking the change in volume to density. Let's have a look in a little more detail - heating is making the particles vibrate more, heating is all about vibrating those particles. The more the particles vibrate, the more space they will take up. This will increase the volume. That is the description part done - I have stated facts. Now I need to make a link between the volume and the density. Because the density is increased and the mass has not changed, the density will decrease.
• Question 8

Describe how to calculate the volume of a cube (2 marks).

EDDIE SAYS
This question is all about seeing if you can remember how to calculate the volume of a regular object. There are 2 basic steps that you need to take for this question (you might have guessed this by the 2 marks :O) 1 - find the length, width d breadth of an object. Normally measuring them with a ruler. 2 - multiply them together to get your density. Boom - done!
• Question 9

Calculate the density of this cube.

Mass of the object = 0.1 kg

800
EDDIE SAYS
This question has a few parts and it is the hardest type of question you will get in the foundation paper. Let's look at the steps. Step 1 - work out the volume of the object. It is a cube, so you are expected to know that all of the sides are the same length. This might be where you make your first mistake - did you convert from cm to m? Each side should be 0.05 m, not 5 m! It should look like this 0.05 x 0.05 x 0.05 = 0.000125 m3 Step 2 - Put this into the density equation: ρ = ? m = 0.1 V = 0.000125 ρ = 0.1/0.000125 &rho: = 800 kg/m3 DONE! Awesome question, right?
• Question 10

Put these objects into an order of most dense at the bottom to least dense at the top.

## Column B

Least dense
Oxygen
In the middle
Ethanol (alcolhol)
Most dense
Aluminium
EDDIE SAYS
Did you get it? There was one option from each of the three states of matter! Oxygen (the gas) was the least dense, because it is a gas. Then it was ethanol because it is a liquid. Finally, aluminium because it is solid.