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This is the one skill every Year 8 Science student needs to have... so they don’t struggle with it in Year 12! Here's our Part 2 step-by-step guide on how to draw and interpret scientific graphs.
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In Part 1 of scientific graphs, we covered how to enter data onto a set of numbered axes accurately. But the real challenge comes now with Year 8 Science graphs, as we move on to working with blank grids!
They might look like this…
Or just like this!
We need to be able to create our own axes from scratch. We’ll follow these steps to draw Year 8 Science graphs from blank grids:
Download your free worksheet to practise the graphing skills you need for high school science.
Most of the data we get from experiments in Year 8 can be arranged in a table like this:
| Force (N) | Distance (m) |
| 1 | 10 |
| 2 | 18 |
| 3 | 25 |
| 4 | 31 |
So, if we’ve got two columns and two axes, does it matter which variable goes on which axis? Yes it does.
When you did your experiment, the data you collected was from two specific variables.
The independent variable belongs on the x-axis (the horizontal axis). The dependent variable belongs on the y-axis (the vertical axis).
If you can’t work out from the design of the experiment which is which, the independent variable is more likely to be found on the left-hand column of the table of data. This is because you can plan how you will vary the independent variable before you start taking measurements, so it’s often written down first.
So we put the variables on the correct axes, with units. Surely at this point we can’t mess this up?
WRONG!
If we put the labels that close to the grid, we won’t have room for our values! Leave a space.
The grid lines each represent a number, but we can’t start every graph at 1 and count 2, 3, 4… What if the values go up to a thousand? Or a million?
We also don’t want to crowd all of our data into one corner of the grid, because that makes it harder to draw and harder to read. Teachers may take marks off if you don’t use more than half of the grid, or two-thirds, or three-quarters!
We can choose a scale that works best for our data. Each line could represent an increase of 1, or 0.1, or 1000 – whatever works best.
Let’s look at our grid again, but I’ve removed the faint lines for clarity.
I must label the lines and not the boxes. To help remind yourself of that, add some tick marks – extensions to each line outside the grid.
You don’t have to label every line! Notice how I didn’t bother labelling 0.5, 1.5, etc? In theory, I could even put 0, 2, and 4 on this graph and leave the 1, 3, and 5 lines blank.
However, it is important to label the line that’s furthest to the left, in this case, with a zero. This is to avoid a CLASSIC STUDENT MISTAKE, as seen below.
See how the 0 and 1 are closer together than the 1 and the 2? That’s not allowed! Every time we go up by one on the scale that we’ve chosen, we go over by two lines.
Now let’s repeat for the y-axis. Another classic student mistake incoming…
Students seem to think that because they put the numbers from the Force column on the x-axis tick marks, that means they can put the exact numbers from the distance column onto the y-axis tick marks. But that’s not a real scale! The difference between 0 and 10 is 10, but the distance between 10 and 18 is only 8!
To avoid this problem, let’s just focus on the biggest value in our table for now, which is 31.
To make our scale, let’s count by tens.
If we make every second line the next tens value, the scale goes up to 50. Our data will cover more than half the graph, but less than three-quarters. Can we stretch it out more?
If we make every third line the next tens value, we only go up to thirty. That’s not enough.
Technically, we could do something like counting by sevens or eights instead! You should probably avoid this unless you’re VERY confident in your mental Maths skills, as it can make it harder to tell intuitively where the data should go if it doesn’t fall exactly on a line. Can you quickly tell where 18 is on this scale, for example?
So going back to our distance axis, we’ll count by tens and create our first set of labelled axes. Time to put the data on and draw a line of best fit. For more advice about this, check out our other blog post.
There are only a few more situations that we need to cover to be masters of axes.
Some data sets aren’t even spread out between zero and the maximum number. Let’s look at one.
| Year | Average Global Temperature (°C) |
| 1980 | 14.2 |
| 1990 | 14.4 |
| 2000 | 14.3 |
| 2010 | 14.6 |
| 2020 | 14.9 |
What does this graph look like if we start both axes at zero? In a word… silly.
If we start the x-axis at 1970 and the y-axis at 14.0, we can actually read the data!
There is one other approach you may see used for data like this is the “zigzag line” approach, aka “the squiggle”. This creates a broken or discontinuous axis, where the squiggled area represents all the numbers we’re not including.
In this case the squiggle represents the temperatures from 0 – 14.1 °C.
In our previous post we covered the extrapolation of lines of best fit to make predictions. Let’s look at the force-distance graph we created earlier.
If we were asked to make a prediction about how far the object would go if we pushed it with a force of 0.5 Newtons, or 5 Newtons, our graph could tell us that.
At 0.5 Newtons the distance is around 7 metres, and at 5 Newtons the distance is around 38 or 39 Newtons (more grid lines or a ruler could help us tell). But what if we want to extrapolate to 6 Newtons? Or 7 Newtons? Our graph doesn’t let us do that.
To prevent this, we must include extrapolation values when we create our scale in the first place. The problem is, questions about extrapolation often come after the question requiring you to draw the graph. This is why it’s essential to read ahead.
There are other skills involved in Year 8 Science graphs. You’ll need to learn how to make neat graphs when the values are in scientific notation, and discover that the gradient (slope) of a line of best fit can often yield unexpectedly deep insights. The gradient of one graph even helped Einstein win a Nobel Prize! And once you’ve learned to read the gradient from a straight line graph you’ll learn about linearisation, which can turn tricky curves into useful straight lines. But for now, focus on getting your axes right, before you become the lost Year 12 student wondering where it all went wrong.
Learn how to read, plot, and analyse graphs with step-by-step examples and practice questions. Download our free worksheet and build confidence in interpreting and drawing graphs!
Download your free worksheet to practise the graphing skills you need for high school science.
Written by Matrix Science Team
The Matrix Science Team are teachers and tutors with a passion for Science and a dedication to seeing Matrix Students achieving their academic goals.
© Matrix Education and www.matrix.edu.au, 2023. Unauthorised use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Matrix Education and www.matrix.edu.au with appropriate and specific direction to the original content.
