Back To CourseEarth Science: Middle School
12 chapters | 101 lessons
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Paul has been teaching middle school science for the last 10 years, and has his bachelors degree in Elementary Education.
You know how superheroes always seem to have secret identities? Take Clark Kent, for example. He works as a newspaper journalist - and is also, by the way, Superman! He simply hides his identity by wearing glasses. His co-workers must not be paying much attention around the office!
Some superheroes wear masks, and a few even have a whole suit that covers them, but they usually conceal themselves somehow. They have secret identities; it's like they just go by a different name at times.
Sometimes we even use different names for things to make them simpler to understand. Today, we're going to be looking at a few terms from the graphing world which have been called by their nicknames for too long; it's time we call them by what they really are. Specifically, this lesson will be looking at the terms scale and range. We'll also be discussing the X- and Y-axes and the concept of scale breaks on a graph.
Have you ever heard of the scale? No, he's not a new superhero who has the ability to change his weight, nor does he have a layer of bony outer coverings impervious to all forms of damage. While that would be pretty interesting, I'm talking about graphs here. Scale is the distance between points on a line. It might be best to look at a graph while we do this to help understand what's going on. Bring out the sample!
In a recent poll, these were the top ways that superheroes arrived at their mild mannered daily jobs. As you can see, some take cars, one teleports to work, a few are even riding the subway! But what I want to focus on is the way the graph is counting. Look at the far left side. See where it says, 'number of superheroes?' That side of the graph is counting by ones. We could say that the scale of this line is by ones. Just like the superheroes themselves, that term scale has a hidden meaning - it's simply a distance between those numbers, or the distance between points on a line.
But what if we had more superheroes? If our numbers were much bigger, we would have a graph that was so long it wouldn't fit here. But we can always change the scale! If we were to count by tens instead, that would make our graph fit into the same physical area. So, if we were to get a larger group of superheroes together and ask them how they all get to work, maybe our numbers would look more like this graph.
As you can see by looking at the graph, we're counting by tens, which means the scale of this line is ten. The graph is physically the same dimensions as before, but now it covers a much larger set of numbers, which brings us to our next term: range. Range means all the numbers in a set of data. If we wanted to tell someone the range of our graph here, you could look at the left side and see that we are counting numbers of superheroes; our range would be zero to 50.
As a quick review, look back at our original graph again. Here we can see that we are counting by ones as we go up the side of the graph. That makes our scale counting by ones. The range of this scale is zero to five.
Just like the scale and range are terms we don't normally hear, there are other parts of the graph, which just like our superheroes, can and often do go by a different name from time to time. For example, the bottom line of the graph is sometimes called the X-axis, and the side line of the graph is sometimes called the Y-axis. These parts are often just called the bottom and the side and that's okay, but you should also know there are other names.
Every graph we make in this lesson will consist of these two lines because they represent our two variables. An axis is just another way to name those lines. Let's just focus on the bottom of our graph first. Sample please?
As you can see, we're looking at a graph of escaped creatures from Mrs. Amiee's classroom. Wow, that's a lot of free roaming hamsters! Looking at the bottom variable on the graph, where it says the type of creatures, you could call this the X-axis. But, all four of these terms (bottom, horizontal, independent variable and X-axis) are referring to the exact same part of the graph. They are like our superheroes in that aspect; they have secret identities but are all actually the same person. So when you see one of those terms, just know that they're all referencing the exact same place.
We encounter the same idea when we look at the side of our graph as well, here labeled the number of creatures. These terms (side, vertical, dependent variable and Y-axis) all mean the same thing for this part of the graph, too. They are, however, different from the other set; don't mix these two groups up.
Let's find another example to look at. Ah, here's a good one, weights of turtles and tortoises.
First, let's practice what we just learned. There are a few terms for that part of the graph labeled 'Name of Animal.' Can you remember any of them? I'll give you a second. Hopefully you remembered that this is called the X-axis, or the independent variable. And how about that left side? Do you think you can remember those? It's called the dependent variable, or the Y-axis.
Also, think back to our scale from before. What is this graph counting by? What's its scale? I know you remembered this! This graph has a scale of 50 and a range of zero to 300. But look at how small the bar is for the painted turtle. There's a way that the graph can be made to display our data better. It's called a line break. A line break is where a line is shown which breaks the scale. This is again best shown by an example. Look at our original graph. Now take a look at what it looks like with a line break in it.
One thing that this does for the graph is to display the information in a more detailed way. It also makes the scale more accurate to read.
You can see that the scale has changed a bit once the break was added; now we're counting by fives. See the split right above the 40-pound mark shown by the two wavy lines? This means that our bar for loggerhead turtles should be much longer; you can see that the numbers jump quite a bit after that break. Line breaks are a good idea for graphs with one or two data points that are much higher or lower than the rest of the numbers. Just show on the graph that there will be a break in the scale somehow. Most graphs use a squiggle or a zigzag line to display this.
Let's review. Today, we focused mainly on the names and parts of graphs. First, we saw how a scale is just the distance between points on a line and how it's the same as counting by a number on that line. After that, we looked at range, which is all the numbers from a set of data.
We also covered two terms that define the two separate lines which make up a graph. The bottom line sometimes is called the X-axis, which represents the independent variable, and the side line, called the Y-axis, which represents the dependent variable. An axis is just another way to name lines on a graph.
Lastly, we looked at making a graph more efficient by using a line break to split our scale on the Y-axis. This made our graph more concise and gave a clear picture of the data being represented. Thanks for watching.
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Back To CourseEarth Science: Middle School
12 chapters | 101 lessons