Steps to this lesson:
​
1. Read this page on Density. Take the time to record answers to questions (Reflecting Moments & Try It Yourself) as well as your thoughts on the videos. When you get to the bottom of the page. Transfer the answers from your notebook to the comment section. Please include your initials.
2. Once you have read through this page and you think you have a good understanding of the material, you may move onto a review activity Read the instructions carefully and complete to the best of your ability. If you have any questions, make sure you ask! It doesnt hurt to ask!
3. Finally, once you have looked through all of the web activities on density. Please log into google classroom and under the Science 8/9 tab there will be a "Density Assignment". Complete the assignment and hand it in on google classroom. That assignment is for marks.
What is Density?
Density is the amount of matter in a given volume. Every substance has a different density, because each substance is made up of different particles. The density of a substance depends on the particles it is made up of. When we talk about density, it's usually mass density we're referring to. . Density depends on whether the object is solid, filled with air pockets, or something in between.
Substances that have a higher density than the density of the substance it is placed in will sink, substances that have a lower density than the density of the substance it is placed in will float.
​
​
Calculating Density Density
​
The mass of a substance divided by its volume, which changes as temperature changes. Density is calculated by dividing the mass of a substance by its volume. The units for the density of liquids and gases are uually grams per millilitre (g/mL).
This is shown in the following equation form:
​
​
​
​
​
​
Reflection Moment : In your own words, how would you describe density?
Try it Yourself : A glass of water weighs 3kg and has a volume of 5m. What is the density of this glass of water?
Example Calculation
Still Confused? This video will help provide an alternative explanation.
​
(work through the problem as the video explains it, this will help you remember and understand it better.)
Before moving on, check out this link with some practice problems on the density! https://quizlet.com/1164352/density-8th-grade-science-flash-cards
According to the particle theory, different substances have different-sized particles. The size of the particles determines how many particles can "fit into" a given space. Therefore, each substance has its own unique density, based on particle size
​
How is the density of a substance related to the substance's physical state? Imagine filling a film container with liquid water and another film container with water vapour. Both liquid water and water vapour are the same substance and therefore have particles of the same size. According to the particle theory, gas particles have more space between them than do liquid particles. Therefore, the water vapour in the container would have fewer particles than the li
quid water. It would be reasonable to conclude that the density of the water vapour is less than the density of liquid water
​
Why can I stand on a solid and not a liquid or gas?
​
When an object moves through a fluid, it pushes
particles apart and moves between them. Particles in
a solid cannot be pushed apart. To understand why,
imagine that you and a few friends are together. You
want to prevent anyone else from pushing your group
apart and moving between you. What would you do?
First, you would have to stand quite close together.
Then you would probably hold on to each other very
tightly. If you do not let go of one another, no one can
move between you. That is what particles in a solid do.
Attractive forces among the particles of a solid are
stronger than those between fluid particles and thus th(
particles in a solid cannot be pushed apart
​
​
If you were to step onto the surface of a lake, the water would not support your foot. Instead, your foot would go right through the water. In fact, you would continue to fall through the water, pushing the water particles out of the way, as shown in Figure 5.5. Liquids cannot support objects in the same way that solids can, because the particles of a liquid move apart easily, allowing a dense, solid object, such as your foot, to pass through the liquid. The attractive forces between liquid particles are not strong enough to prevent your foot from pushing them apart.
​
​
​
​
​
​
​
​
​
​
Similarly, you cannot walk on air, because gases are even less dense than solids or liquids. When you move through air, you are moving through mostly empty space. You do not have to move as many particles of air out of the way as you do in*water (see Figure 5.6). This explains why running through air is much easier and faster than running through water. In general, gases are less dense than liquids.
​
If an object changes state (ie. from liquid to solid or solid to liquid), the density will change!
​
As temperature increases, a substance will change from solid, to liquid, to gas. The particle theory states that the particles of a substance spread out as they gain energy when heated. Thus, the particles take up more space, which means that the density of the substance decreases. It is almost always true that, for each pure substance (for example, gold), the density of its solid state is greater than the density of its liquid state. The substance's sohd state and Hquid state are, in tum, denser than its gaseous state.
​
