Defining and Explaining Density
You might be wondering, “What is density?”
In simple terms, density is a property of measurement that determines the amount of space which is taken up an object or a substance. It is a property that compares the amount of matter which an object has concerning its volume. Another way of defining density is that it is the amount of mass present within an object about its volume.
If an object is heavy yet compact, the object is a high-density object. On the other hand, if the object is small and yet it takes up a lot of space, it has a low density.
The concept becomes a lot easier once we relate it to dodgeballs. Have you ever wondered why don’t foam balls hurt? Contrarily, why DO rubber balls hurt when they hit us? It all occurs due to a form of measurement known as density.
If you remember, in a previous section, we raised certain questions regarding foam and rubber balls. Now that you know about the basis of density, you can easily answer all such questions.
Simply said, foam balls are low-density objects. They are small and light objects. In spite of this, they occupy a lot of space. As a result, they don’t hurt as much as rubber balls.
Rubber balls, on the other hand, are high-density objects. They are heavy and yet they don’t occupy a lot of space. This makes them highly compact. As a result, they don’t hurt a lot when they find you as their target.
The formula of density depends on two important properties, namely mass, and volume. These properties are discussed in detail below.
The first constituent of density is mass. Let’s start with it. We have learned before that mass refers to the amount of matter, constituted within an object or substance. It is a universal property of measurement which does not change even when there are changes in the environment around the object or substance.
An object on earth with a certain mass has the same mass in space. It is commonly measured in units, namely grams (g) or kilograms (kgs).
Volume is the second constituent which determines the density of an object. It is the property that determines how much space an object or substance takes up. It is measured in cubic units, such as cubic centimeters (cm3) and cubic meters (m3).
Mass and volume are what ultimately constitutes density’s formula. It is represented as:
Density = Mass / Volume
To find the density of an object or substance, you need to divide the mass of an object by its volume.
The Distinguishing Properties of Mass and Density
In the realm of Physics, there are several properties used to define or describe matter.
Two such properties are mass and density. Not only are mass and density highly alike in nature, but they also share a close mathematical relationship. Owing to this, they are often confused with one another.
However, differentiating between mass and density isn’t that tough if you get a basic understanding of the properties. A few differences which can help you to discriminate between mass and density:
1. The Basic Definition – Mass refers to the amount of matter which is contained within an object. Density, on the other hand, refers to the concentration of matter within an object.
2. The Uses – Mass is used to gain a measure of inertia. On the other hand, density lets you know how compact an object is.
3. The Units – Mass is measured in units such as kilogram or kg. Alternatively, density is measured in kilograms per cubic meters or kg/m3.
Density of Liquids
The concept of density, in association with solids, might have become abundantly clear now. But what about liquids? Do they also share the property of density with their liquid counterparts?
Apparently, yes they do. Similar to solids, liquids have their characteristic density. The density of any liquid depends vastly on the mass and size of the molecules present within the liquid.
Moreover, it also depends on how closely packed these molecules are. The one other similarity which liquids share with solids is the volume. Similar to solids, liquids also have a definite volume.
This volume neither depends on the size or the shape of the container.
Measuring the Density of a Liquid
Numerous people presume the process of measuring the density to be a tough one. However, this is never the case.
Measuring the density of a liquid is easier than measuring the density of a solid. This is primarily because the volume and mass of a liquid can be directly and simultaneously measured.
To measure the density, you will require a volume-measuring container. It could be any form of a container, provided it has the markings that facilitate volume measurement.
At a lot of times, these containers are accompanied by a scale that can measure the mass of the liquid. This makes the process a hundred times easier.
Following this, you will need to comply with these steps:
1. Start by calibrating the scale. Manually adjust the scale until the scale reads a “0” with the container on top.
2. Add the liquid to the container to measure the volume of the liquid.
3. At this point, you will need to record the measurements. Often, it so occurs that the surface of the container is curved. In the event of this, check out the direction in which the container is curved. If the surface is curved upwards, record the top of the curve. Conversely, if the surface of the container points downward, record the volume at the bottom of the curve.
4. Once you are done with recording the volume, record the mass as displayed on the scale.
5. Finally, calculate the density of the liquid by applying the recorded values within the formula of density.
Floating and Sinking of Objects
One of the most important concepts associated both with the density of solids and liquids is the floating and sinking of objects.
You might have noticed that certain solids, when placed in certain liquids, tend to float in some while sinking in others.
Have you ever wondered why is it so? Why do some solids float in some liquids while they sink in other liquids?
Well, the simple answer to this phenomenon is that it is also associated with density.
Whether an object sinks or floats in a liquid depends immensely on the density of the solid as well as that of the liquid in which it is immersed.
An object whose density is greater than that of the liquid will sink in it. On the other hand, an object which is less dense than the liquid tends to float in it.
Relative density refers to the ratio of the density of a substance in respect to the density of another referenced material.
When it comes to choosing a reference material, water is one of the most preferred choices.
Due to this, relative density is also referred to as specific gravity since specific gravity refers to the relative density of a substance in respect to water.
The formula used for representing relative density is:
Relative Density = Density of a Substance / Density of the Referenced Substance
Relative density, once calculated, can be interpreted in three different ways. These include:
1. When the relative density is lesser than 1 – If the relative density is lesser than 1, it indicates that the substance is less dense than the reference substance.
2. When the relative density is equal to 1 – If the relative density is exactly equal to 1, it indicates that the densities of both substances are equal. In essence, it means that equal volumes of both substances have the same mass.
3. When the relative density is greater than 1 – If the relative density is greater than 1, it indicates that the density of the substance is greater than the reference.
A Few Facts Associated With Density
1. Density and buoyancy are closely related – In the floating and sinking of objects section, we discussed that denser objects sink in less dense liquids and vice-versa. This is what connects density and buoyancy. Their relationship can be defined as an increase in volume decreases density while increasing the buoyancy force.
2. Used in cases of weight and weight distribution – In certain tasks, such as the construction of ships, buildings, airplanes, etc. weight and weight distribution are highly important. In such cases, density measurements are extensively used.
3. A Natural Property – Density is an intrinsic property of all substances. Therefore, the density of all instances of a particular substance is the same regardless of their size or their shape. Owing to this property, we can identify unknown materials by determining their density and comparing it with the list of known substances.
Activities For Teaching Density To Kids
Even though this article makes density an easy concept for children, there are still some kids who may feel overwhelmed by the concept. A few easy concepts for teaching such children include:
1. With the help of different layers of liquids
In this activity, you can help your students to understand density by showing them the different layers that form when you add liquids of different densities. All that you need is some vegetable oil, water, other liquids such as golden syrup, milk, etc. You can check out the entire density rainbow activity here.
2. An aquarium and some balls – For this activity, you need an aquarium and some balls made of different materials.
Once you fill the aquarium with a liquid, you can ask your students whether a particular ball will sink or swim. The full activity can be found here: http://www.proteacher.net/discussions/showpost.php?p=380278
3. A Sink or Float Activity – Get a bucket of water into your classroom. Along with it, get certain everyday objects that you can find in the vicinity of your classroom.
These could be anything, either solid or liquid. Before actually carrying out the experiment, let your children guess whether the objects will sink or float. Once they are done with this, perform the activity and check out the students having the most number of correct answers.
These students could be offered some form of a reward for being right. A few summaries of this experiment can be found right here: https://www.giftofcuriosity.com/sink-or-float-density-activity-for-kids/
4. Salt Water and Fresh Water – With the help of this experiment, you can show your students how saltwater is denser than freshwater.
You can do this by weighing or balancing equal quantities of both. For more details, regarding this activity, you can check out: http://www.proteacher.org/a/29599_Salt_water_and_fresh_water..html
5. With the help of eggs, salt, and water – This is another float or sink method for teaching children how gravity works. However, it is different in the form that it changes the liquid’s ability to sink or float the object.
You will need an egg, 2 glasses, measuring spoon, table salt, and water. Pour water in both glasses but add salt just in one.
Now drop the egg in the glass with no salt. It will sink. However, when you add the egg in the glass with saltwater, it floats. Explain why this happens with the help of this: https://www.education.com/activity/article/teach_density_fourth/