Lesson video

Hello, my name's Mrs. Navin, and today we'll be talking about variables as part of our topic on solutions.

You may have come across variables in some of your prior learning, but you'll definitely be talking about them going forward in your journey through science because they form the basis of all of our science experiments and it's these experiments that help us to answer that big question of how can we explain how substances behave? So by the end of today's lesson, you should be able to identify an independent, dependent, and control variable, for an experiment and also be able to describe the differences between each of those.

The keywords that we'll be using in today's lesson include variable, independent variable, dependent variable, control variable, and fair test.

Now the next slide shows the definitions of these keywords being used in a sentence, and you may find it useful to pause the video here to read through them and perhaps make a note of those definitions to refer to as we go through in today's lesson.

Today's lesson will cover three main things, firstly, variables and values.

Then we'll look at changing or measuring variables, and we'll finish off today's lesson by looking at fair testing.

So let's get started by looking at variables and values.

First thing we need to understand is that anything that can change or vary is called a variable, and you'll have experiences of lots of different things that are a variable.

The most common one is probably temperature.

You'll notice that as soon as you pull back your covers in the morning, you might feel a cold temperature.

If you go outside, that might be a different temperature, and temperatures can vary from building to building, day to day, season to season, all sorts of things.

Another variable that might change season to season is the hours of sunlight you experience between the spring and summer months versus the autumn and winter months.

In fact, as you make your way from place to place throughout the day, you'll see another variable as simple as the different car colours that you come across in that journey.

Now, how a variable actually changes is known as its values.

So if we look at that variable of temperature, again, the different values it could have are these.

The simple measurements of those temperatures could be described as the values for the variable of temperature.

If we look at that variable of sunlight, the possible values that we could give it are the actual numbers of hours.

Do you have six hours of daylight? Do you have 12, perhaps 18? So those are some examples of values for these particular variables.

I'd like you to have a go now and come up with some values, sorry, for the variable of a car colour.

You might like to pause the video here and come back when you're ready to check your work.

Let's see how you got on.

There were so many different options you could have put here.

These are some that perhaps you have suggested.

The colours of a blue, black, silver, grey, red, yellow, green, gold.

Any colour you can imagine could be considered a value for the variable of car colour.

Let's have a go then at our first task.

What I'd like you to do is to complete these sentences.

Pause the video here and come back when you're ready to check your work.

Let's see how you got on.

Well, for sentence A, it should read an aspect of something that can change is known as a variable.

And for sentence B, how that aspect changes is called its values.

Well done if you've got those two key terms in the correct places of those sentences.

For the next part of this task, I'd like you to look at this table of variables and possible values, and I'd like you to either suggest some possible values for that variable, or suggest what the variable is called based on the values that have been provided.

Pause the video here and come back when you're ready to check your work.

Let's see how you got on then.

So there were a lot of different things that you could have said for either the, for the values in particular, but you might have suggested for instance, for the length, some different numbers, values, and some units.

So here we have offered perhaps two, five, a hundred centimetres.

You may have suggested something along the lines of metres or miles or kilometres.

The key though, when offering different values is having the measurement for them, the units themselves are insufficient.

You need to have a number to go with them for it to be a possible value.

For the values of 10 grammes, a hundred grammes, or 1.

5 kilogrammes, hopefully you've noticed that that is the values that you would associate with mass.

For volume, these ones again, you could have had a variety of answers here.

I've suggested centimetres cubed as the possible values, and again, remember I've added some numbers with those.

So five centimetres cube, 25, or a hundred centimetres cubed.

Some other values you might have used could have had the units of metres cubed or pints.

You might have had gallons, you might have had litres.

But again, regardless of the unit that you're using, the value has to have some kind of measurement involved, so a number.

Finally then for those last possible values that have been suggested, hopefully you've recognised the S as being seconds and therefore those are values for the variable of time.

Well done if you manage to have a go at that and get a few of those correct.

Good job guys.

Now that we're feeling a little bit more comfortable understanding variables and being able to suggest some values for them, let's look at the difference between changing or measuring variables.

The other thing that we need to understand is that scientists conduct investigations in order to gather evidence that's going to help them to answer a question.

So for instance, if we wanted to know if the amount of sunlight affects the temperature that's being measured, we would need to consider and classify the variables involved in that question so that the evidence that we're gathering is useful and valid in order for us to be able to answer that question confidently.

Now, if we take a closer look at this question, does the amount of sunlight affect the temperature? There are two variables within that question.

There's the amount of sunlight that could change and then the temperature that could change.

Now one variable will be changed and the other variable will then be observed or measured, and it varies because the other variable is what has been changed.

Seems a little confusing.

But now that we've at least identified the variables in our question, we need to now classify them.

What's being changed and which one's being observed and measured.

So in any investigation, the variable that is being changed is known as the independent variable, okay? It's not reliant on something else, it's something that we are changing ourselves.

And in this investigation, it's the amount of sunlight.

Now, I know it's not something that we can control, but it is something that is changing and we can monitor that.

The other variable in an investigation then is what's being observed or measured, and that's known as the dependent variable.

So our observations, our measurements, depend upon how that other variable has been changed, and in our example, does the amount of sunlight affect the temperature? What we're measuring is that temperature, our observations are how that temperature is being changed as a result of the amount of sunlight.

Let's look at another example where we try to identify the independent and dependent variables for an investigation.

So for this example, I would like to know, does the volume of water affect the size of the flowers that are produced? So the first thing I need to do is identify the variables within that question.

And for this example, I would say that the variable is the volume of water that's being used and the size of the flowers produced.

The next thing I need to do then is decide which of those two variables is the independent variable and which is the dependent variable.

So the one that I can control, the one that I can change myself, is going to be the volume of water.

That's gonna be the independent variable.

The dependent variable then, the thing that I'm going to be observing or measuring, is gonna be the size of the flower, and that is dependent upon how my independent variable, the volume of water, has changed.

Now that I've done an example, I'd like you to have a go yourself.

So I'd like you to identify the independent and dependent variables in this example.

Does the temperature affect the number of ice lollies sold? Pause the video here and come back when you're ready to check your work.

Let's see how you got on.

So the first thing we needed to do was to identify the variables within that question, and hopefully you chose temperature, a number of ice lollies.

The next thing that we need to look at is to classify each of those as either the independent or dependent variable.

And in this instance, it's the temperature that is the independent variable and the dependent variable then, is the number of ice lollies that are being sold, is it being affected by that temperature changing? Well done if you got those correct.

It's okay if you didn't quite get the classification of independent and dependent variable correctly.

If you are able to identify the variables in the first place, that's the first step in order to make those decisions.

So well done, good job guys.

Time for our next task.

So the first thing I'd like you to do is to match each keyword to the correct definition.

Pause the video here and come back when you're ready to check your work.

Okay, let's see how you got on.

Right, the first keyword we have here is variable, and a variable is the second definition of any aspect in an investigation that can vary.

So it's a very vague definition.

An independent variable then, we need to be a little bit more specific in our definition, and that's the part of the investigation that is being changed.

The dependent variable then is what is being observed or measured, and it depends on how that independent variable has changed in the first place.

So well done if you managed to match those keywords up correctly.

For the next part of this task, what I'd like you to do is to look at each of these investigation questions and decide what the variables are, and then to classify them as being either an independent or dependent variable.

You may find it useful to refer to your answers for question one of this task as as you go through, but definitely pause the video, and then come back when you're ready to check your work.

Okay, so let's see how you got on.

For part A, the question was, does the length of the rubber band affect the distance a paperclip travels when it's launched? And the independent variable here then is the length of the rubber band.

You can just simply swap out your rubber bands.

The dependent variable then is the distance that's measured when a paperclip then travels.

For question B, the question was, is the time taken for a loaf of bread to bake affected by the type of flour that's being used? So the independent variable, the thing that you can easily change, is the type of flour that's used.

The dependent variable, what's being observed or measured, is the time taken for that loaf of bread to bake.

For part C, does the type of a metal a spring is made of affect the distance it can extend? The independent variable was the type of metal.

You can simply swap out the spring based on the metal that it's formed from.

And the dependent variable, what you're measuring, is the distance a spring can then extend as it's stretched.

For Part D, is the speed a car can travel affected by the width of its tyres.

The independent variable is the width of the car tyres 'cause those can be changed out very easily.

The dependent variable, what's being measured or observed, would be the speed the car is travelling at.

And the last part E question then, does the colour of suitcase affect how often it is lost in transit? The independent variable then would be the colour of suitcase.

So you can simply take lots of journeys with a different coloured suitcase and the dependent variable then would be recording and observing how often it is lost in transit.

Now this is quite a lot of information to try and keep track of in one particular task, and sometimes the wording can get a little confusing.

So I would almost recommend in questions like this going forward, if you're struggling to, one, identify those variables, or two, to classify them, consider using two different highlighters or two different pens, or maybe putting circles around the independent variable and squares around the dependent variable.

Just something that will help you to keep them clear in your head and identify them.

It just makes it a little bit easier to classify and identify them as you go forward, but very well done on what can be a challenging task when there's so many words to keep track of.

So, well done.

Let's now look at the last part of today's lesson, fair testing.

Now, I mentioned at the start of today's lesson that scientists conduct experiments in order to collect evidence, in order to answer a question.

But for that evidence to be considered useful, it really needs to be collected using a fair test.

Now, a fair test is an investigation that takes place in which only one variable has ever been changed.

Let's return to that original question of, does the amount of sunlight affect the temperature? Besides the sunlight and the temperature that we identified as variables earlier, what other variables, what other things, could change in this investigation? Well, there's quite a few.

If we think about it, other variables might include the material that you're actually measuring the temperature of.

Are you measuring the temperature of a piece of metal, a glass of water, a cup of tea? So that material could actually affect the temperatures that you're measuring.

How much of that material are you using? Are you using an A5 sheet of metal? Are you using 50 centimetres cubed or 250 centimetres cubed of water? That might affect the temperature that's being measured.

What's the starting temperature of the material you're using? Does it matter if the starting temperature of your material is different? All of these particular other variables, the other things that might impact on my measurements, are known as control variables.

All the other variables are control variables.

So for an investigation to be considered a fair test, these other variables need to be kept constant.

That means the same or unchanging, throughout the entire investigation.

Controlling those other variables means then that they're not affecting the dependent variable, that thing that you are observing or measuring.

So why is that such a big deal? There's a very important reason.

If you are not controlling those other variables, they could be affecting those measurements and observations that you're making.

And if that's happening, the results that you're collecting could be incorrect.

That then means that the evidence you're collecting to answer a question won't be so strong.

And the knock on effect of that then is that the results you're collecting won't be acceptable to confidently answer the question that you're trying to answer.

People will question your answer to that question, and we really want to try and avoid that.

Let's return to an earlier an example to try to identify some control variables.

So we asked earlier, does the volume of water affect the size of the flowers produced? And we identified the two variables, the independent and dependent variables, as being this.

The independent variable was the volume of water and the dependent variable was the size of the flowers produced.

So I need to consider what are some of the other control variables? What do I need to keep the same to ensure that the size of the flowers that I'm measuring, isn't being affected by anything else other than the volume of water.

So I've had a think, and these are some that I came up with.

I need to make sure that I'm always measuring the same type of flour.

I'm not gonna compare a rose against a dandelion, against a lily.

I also might wanna consider the time of day that that flower is being watered.

Is it being watered at the beginning of the day after perhaps there's quite a lot of dew on the ground? Or is it being watered at midday when the sun is highest? And the possibility of that water evaporating is going to be a little bit higher? Where is this flower actually being grown? Is it being grown in the ground where it might have access to rainwater? Or is it being grown in a pot where the only water that it has is the water that I've put in? And is that pot inside in a conservatory perhaps, or is it outside? I might also wanna consider whether or not there's fertiliser in any of the soil.

For instance, if the flower is in the ground, there might be other nutrients available to it that it wouldn't have if it was in a pot.

So lots of different things that we would need to consider in order to make sure that my dependent variable isn't being affected by anything else.

And I wanna point that out here is that we only have ever one independent variable, one dependent variable, but there can be many control variables.

And I would always challenge you to find about two or three control variables that you would need to consider in any experiment as a minimum.

And when you find out what those control variables are, consider how you might control them.

So I'm gonna give you an example now, and I'd like you to try and find the control variables for the example you looked at earlier.

You identified that the temperature was the independent variable and the number of ice lollies sold would be the dependent variable.

I'd like you to think about what control variables you might need to consider to answer that question.

And if you've finished that, think about how you might control those.

Pause the video here, and come back when you're ready to check your work.

Let's see how you got on.

Now as I said, there's gonna be a lot of different answers that you could possibly suggest for control variables.

Some of the ones that I came up with was maybe the brand of the ice lolly that is being sold.

One might be more popular than another.

Maybe the location of the shop.

So how easy is it to purchase that ice lolly? What's the price of it? Is it affordable or not? What time of the day or the week or the year? I mean, how often would you buy an ice lolly first thing in the morning versus midday, or later in the afternoon? And do the weather conditions, so even if it's the summertime, does it matter if it's raining in the summertime? Will that affect perhaps the number of ice lollies that are sold? So there's a lot of different things that we could consider here.

Well done if you managed to come up with at least two or three of these possible control variables.

And even better well done if you managed to come up with ones that I didn't list here.

Good job guys.

Let's have a quick check to see how you're getting on about fair tests.

I would like you to consider if this statement is true or false.

For evidence to be considered valid, a fair test must be conducted.

Well done if you said true, but why? Is it because a fair test is one in which controlling any variables is optional? Or is it because a fair test is one that controls all the variables other than the independent or dependent variables? Good job, if you decided it was B.

A fair test is one that controls all the other variables other than the independent and dependent variables.

Okay, time for our final task of today's lesson, what I'd like you to do first is consider what Sam has been doing.

Sam has been summarising what they've learned in science, but some of their comments seem a little confused.

So what I'd like you to do is read through what they've written down and I'd like you to correct any of the mistakes that you find.

You'll probably want to pause the video here and then come back when you're ready to check your work.

Okay, let's see how you got on.

Now, if you read through each of Sam's summary statements, there was something that needed to be fixed in each one of them.

And I'm gonna go through these individually.

So in the first of their statements, I would've changed it so it reads, aspects that can change are called variables.

In the next one, I would've changed it to read, the aspect that is measured in an investigation is called the dependent variable.

In the next, change it so that it reads, a fair test is one in which only one aspect is changed.

In the next one, this was a trickier one to try to change, but I would've changed it so it reads like this, control variables can have an impact on investigations and they must be kept constant.

And the final statement, I would've changed it so it reads, the aspect that has changed in an investigation is called the independent variable.

Those were some difficult changes to make, but well done for having a go.

For the second part of this final task, I'd like you to consider the investigation that Sophia is conducting.

She's looking if the surface area of the limestone pieces affects the time it takes for them to fully react with acid.

What I'd like you to do is to identify the independent, dependent, and at least two possible control variables for her investigation.

And you may find it useful to use the images here to help guide you a little bit in your answers.

So pause the video here, and come back when you're ready to check your work.

Okay, let's see how you got on.

So the independent variable in this situation is the surface area of those limestone pieces.

The dependent variable then, what she's measuring, is the time taken for those limestone pieces to fully react.

There were quite a few different control variables that you could have suggested.

Hopefully you got a few different suggestions from the pictures that were there to help guide you.

But you could have said something along the lines of the mass of the limestone that's used, the volume of the acid that she's using, the strength or the type of the acid that she's using as well would've been acceptable.

So well done for having a go at that.

And again, well done if you managed to suggest some control variables that I didn't suggest.

I do wanna point out that if you are suggesting they use the same balance or the same size conical flask, or something like that, that's not an acceptable control variable.

That is a choice of apparatus and that will affect the precision or the accuracy of your measurements, but it does not affect the control aspect, the controlling of the variables that we're talking about here.

The other thing I want to point out is that being able to identify variables, particularly those control variables, and thinking about how to control them, can get confusing at times and it takes practise.

So it doesn't matter what experiment you're doing in future, I would always challenge you to constantly remind yourself what is the independent variable here? What is the dependent variable? And what are those control variables? How am I going to control them? Because the more you practise it, the easier it gets, and you'll find that in some instances you are suddenly doing it by second nature and not having to think about it quite so much anymore.

Very well done today on a lesson that can get a little confusing at times.

Good job.

Finally, let's summarise what we've learned in today's lesson.

We've learned that any aspect of an investigation that can change is known as a variable, and variables can be classified in many ways.

The one variable in an investigation that is changed is called the independent variable.

The variable then that is measured, or observed in an experiment, is known as the dependent variable.

And all those other variables that could be changed in that one investigation are known as controlled variables because they need to be kept the same to ensure that that investigation is a fair test.

And that's really important so that the evidence that you're collecting is going to be useful evidence that can help you to more confidently answer a question about an experiment.

I hope you've had a good time learning with me today and to see you again soon.