Hello and welcome to today's lesson.

My name is Mrs. Mehrin and I'm so excited to be learning with you today.

We are going to be learning all about Mohs scale of hardness.

Welcome to today's lesson from the unit Rocks and Soils.

Your lesson outcome today is, I can learn more about the hardness of rocks from the work of important scientists.

Today you're going to be doing lots of new learning, and I know that learning can sometimes be a little bit tricky, but that's okay because we are going to work together and learn lots of fabulous new things.

Let's go through your key keywords for today.

Now I will refer to these keywords throughout the lesson.

But if you'd like to, you can pause the video here and jot them down.

Fantastic, well done.

And here are all of the definitions for those keywords.

Again, I will be referring to these keywords throughout the lesson, so you don't need to jot them down if you wouldn't like to.

However, if you would like to, you can just pause the video here and do that now.

Fantastic, well done.

So your lesson today is split into two sections.

Let's begin with the first one, which is scientists help us to learn about rocks.

Scientists called geologists study what earth is made of.

They help us to learn and understand more about rocks.

Geologists carry out investigations to compare and group different rocks on the basis of their physical properties.

So here in the picture we have a geologist who is observing rocks really closely.

There are lots of ways to observe and measure the physical properties of different rocks.

We can scratch the surface of rocks to find out their hardness, and we can use the results of our tests to decide which rocks to use for different purposes.

Now, geologists, they investigate rocks in lots of different places.

They may investigate volcanic rock, rocks in a mine, and rocks in a glacial lake.

Now these are just some of the places.

There are many, many more.

So let's go through and do a quick check-in of your learning so far.

What does a geologist study? Is it what the earth is made of, what the sky is made of, or what the oceans are made of? I'll give you five seconds to think about your answer, but if you are going to need longer, that's absolutely fine.

You can pause the video here and you can come back to our lesson when you are ready.

Off you go.

Fantastic, well done.

The answer is A, what the earth is made of.

Geologists study what the earth is made of.

Fantastic, well done.

Let's do another check of your learning.

Which of these careers could help us to find out more about rocks? Is it A, a dentist, B, a firefighter, or C, a geologist? I'll give you five seconds to think about your answer.

But if you need longer, you can pause the video here.

Off you go.

Fantastic, well done.

The answer is of course a geologist.

well done.

Now here we have Jacob, and Jacob is investigating like a geologist, and he has scratched the surface of different rocks with a nail to test their hardness.

And Jacob says, "The problem I had using sorting circles was the rocks ranged from very hard to quite hard to not hard." So here he's only grouped them into two sections, hard and not hard, but he's saying there's a circle in between, an option in between, where they're quite hard.

So is there something else that Jacob could be doing to help him to sort these rocks? I'll give you five seconds to think about your answer, but if you need longer, that's absolutely fine.

Just pause the video and come back when you are ready.

Off you go.

Fantastic.

Well done.

So this is your first task.

You are going to present the information, from your own or Jacob scratch test investigation.

So you will have done this in the previous lesson.

And if you haven't done it, that's okay.

You can do that now.

And you're going to show the order of results, rather than hard or not hard in sorting circles.

So you need to show how some rocks can be in between hard and not hard, and therefore they're not in a definite group.

So here are the results of Jacob's scratch test investigation.

So have a really good think, with your scratch test and Jacob's scratch test, how could he now order these without using those two circles, hard and not hard, to sort them? I'll give you some time to think about that answer.

So you may like to just pause the video here and go off and have ago and come back when you are ready.

Off you go.

Fantastic, well done.

So this is how Jacob has decided to rank the order of hardness.

You may have done something quite similar.

So Jacob here has put his rocks from most soft to most hard.

So he's got chalk as the most soft rock, followed by sandstone, then limestone, then marble, and then gneiss.

So it says chalk crumbled, sandstone showed a deep scratch.

It didn't crumble, but it did show that deep scratch.

Limestone showed a little bit of a scratch and a little bit of crumbling, but not as much as sandstone and chalk, and marble showed a slight scratch.

So we're talking just a really, really, really tiny amount, and gneiss showed no scratch at all.

So Jacob knows that this is the order of the rocks from most soft to most hard.

Now, did you do something similar or did you choose to do something different? So now we are onto the second part of our learning, which is developing a scale of hardness.

So here we have Friedrich Mohs, and he was born in Germany in 1773.

He was extremely interested in rocks and what they could be used for.

Now, in 1801, he started to study the different physical properties of rocks in his collection, and he wanted to use this information to organise rocks into groups because no one had ever done this before.

So let's do a quick check-in before we move on, just to make sure that you know who Friedrich Mohs is.

So it says here, Friedrich Mohs was a famous scientist from the past who helped us learn about which of these things.

Was it, A, plants, B, rocks, or C, animals? I'll give you five seconds to think about your answer.

But if you need longer, that's absolutely fine.

You can pause the video here and have a go.

Off you go.

Fantastic, well done.

The answer is of course, B, rocks.

Now, Mr. Mohs knew that rocks are made up of different materials called minerals, and he observed that some minerals are very soft and others are extremely hard.

And he developed a set of numbers called a scale to compare hardness by how easily different minerals could be scratched using different objects.

Now, Mohs' scale is a list of minerals arranged from the softest, so number one, to the hardest, which is number 10.

So he found that talc is the softest as it can be scratched by all other materials, and diamonds with hardest.

Although scientists today have discovered that there are several minerals that are harder than diamonds.

But at the time when Mohs was doing this, he discovered that diamonds was the hardest.

So let's do a quick check-in of your learning, and it says, which of these things did Friedrich Mohs help us to learn about through his investigation? Is it A, how volcanoes are formed, B, the shape of the earth, or C, the properties of rocks? So I'll give you five seconds to think about your answer.

But if you need longer, that's absolutely fine.

Just pause the video here and come back when you are ready.

Off you go.

Fantastic, well done.

The answer is C, the properties of rocks.

So geologists continue to learn about the physical properties and uses of rocks.

So it's ongoing.

It's not something that they've just stopped and we found all of the rocks.

They're continuously finding new rocks and learning new things about the properties of rocks, and they compare the results of their investigations to what Mr. Mohs did and found out.

So Mohs' scale is still very useful to us, and it helps us to determine the hardness of other rocks, decide what different rocks can be used for, and identify an unknown rock.

So quick check-in of your learning so far.

True or false.

The results of a scientific investigation can be compared to other investigations that have already been carried out.

Is that true or is that false? So I'll give you some time now to think about your answer.

If you need to, you can pause the video and you can come back when you are ready.

Off you go.

Fantastic, well done.

The answer is true.

Let's see if you can justify your answer.

So is it because A, geologist today compare their investigations with the findings of scientists like Mohs to see if they've discovered anything new, or is it B, geologists today compare their investigation with the findings of scientists like Mohs as they are lazy? So I'll give you five seconds to think about your answer.

But as always, if you need longer, just pause the video here.

Off you go.

Fantastic, well done.

The answer is A, geologists today compare their investigations with the findings of scientists like Mohs to see if they've discovered anything new.

It's not because they are lazy.

So here is your second task.

It says try a Mohs test using different objects to scratch and compare the rocks in your collection.

So you're going to be using your results from task A and your rocks from task A as well.

Now, you are going to need the following equipment, steel nail file, a coin, and your fingernail.

And you're going to use the information to help you to find out the following things.

So hardness of nine, a rock can be scratched with the tip of a steel nail file, and that's because those are very sharp.

Hardness of three rocks can be scratched with the edge of a 1p coin.

And the hardness of 2.

5, a rock can be scratched with a fingernail.

So if the rock is really hard, it's hardness of nine and can be scratched with the tip of a steel nail file.

Hardness of three, it's with the coin, so it's less hard than the hardness of nine, and hardness of 2.

5 can be scratched with your fingernail.

So remember Mohs' scale.

It goes from soft to hard.

So I'd like you to have a go at that activity.

You're going to need to pause the video here, and have a go at that and compare the rocks in your collection using a Mohs' test, using different objects to scratch them.

Off you go.

Fantastic, well done.

So we have Aisha and Andeep here.

And Aisha says, "I found that chalk could be scratched very easily with my fingernail.

So I rated it at one on my scale." And that would be right because most scale starts at one which is the softest rock.

Now she says, "I could scratch granite a bit with a nail file, so I rated it at nine on my scale." So it takes a lot to scratch granite, but she was able to do so with a nail file.

Now, Andeep says, "I found that some rocks could not be scratched with a coin, but they could be scratched with a nail file, so they must have a hardness rating somewhere between three and nine." So now what you are going to do is to present the findings from your scratch test to show the range of results using a scale.

So your scale could range from 1 to 10, or it might be different.

So you could use your own surname for the name of your scale, similar to what Friedrich Mohs did.

Now, I'm going to give you some time to have a go at presenting your findings from your scratch test, and show it on a scale.

Again, it could range from 1 to 10.

It might be different to that.

I'd like you to pause the video here and have a go.

Off you go.

Fantastic, well done.

So here we have someone who's done this test, and it says, "After testing my rocks using a 1p coin, a steel nail file, and my fingernail, I ordered them from softest to hardest.

Then I added a scale which showed the softest rock, chalk, as number one, and the hardest rock, granite, as number nine.

I named the scale with my own surname." So have a look at yours.

Is it similar or is it different to how it's been done here? Did you remember to create a scale for the hardness of the rocks? I'll let you pause the video here so you can have a really good look at yours and compare it to the results here.

Off you go.

Fantastic, well done.

So now it's time for our summary.

Geologists study what the Earth is made of and help us to understand more about rocks.

Scientists from the past, today, and in the future help us to learn about the physical properties and uses of rocks.

The results of a scientific investigation can be compared to other investigations that have already been carried out.

Now you have done so much new learning today.

I am so proud of you.

You have been really resilient and tried your best, and you've used your critical thinking.

Well done.