Lesson video

Hi there, everybody.

My name is Mr. Booth, and welcome to your Design and Technology lesson for today.

It's brilliant that you could join me.

We have a great lesson today where you are gonna be testing physical properties of materials.

It's important that we can test the physical properties of materials if we are gonna select materials for products based on those physical properties.

And today, we're gonna carry out three tests so you can do that.

This is part of the Materials Testing unit.

Today's outcome: I can test the physical properties of materials.

It's as simple as that.

We have three tests we are gonna do today.

They are about density, absorbency, and electrical conductivity.

So they, of course, are our keywords as well.

So density, a measurement of mass per unit volume.

We then have absorbency, the ability of material to soak up liquids or moisture.

Electrical conductivity, the ability of material to allow electricity to flow through it.

Look out for these keywords during the lesson.

Three learning cycles today, one for each of the tests you are gonna carry out.

So let's start with density.

Density is a measurement of mass per unit volume.

Mass is a measure of how much matter something contains, and we usually measure this in grams. And then we have volume.

This is how much 3D space matter occupies within whatever material we are looking at.

And this is usually measured in centimeter cubed or sometimes you get it in millimeters cubed.

Now, these materials I'm about to show you range from low to high density.

All shapes have the same volume.

So let's have a look at them.

So here we have one shape, here we have another, and here we have another.

And you can see we go from low density through medium density to high density.

But you can see they have the same volume, they are the same size.

Now we can carry out a test to measure a material's density.

So let's have a look at how we might actually do that.

Firstly, a quick check for understanding.

Which of these objects has the highest density? Is it A, B, or C? Pause video now, have a go at this and come back to me when you've answered it.

It is, of course, A, that one has the highest density you can tell because of the matter that's inside it.

So to calculate a material's density, let's all look at how we're gonna do this.

So first of all, we're gonna measure the mass of the material in grams. So we're gonna use a digital scale to do this.

And in this case, the mass of this material, which is a test piece, an imaginary test piece, it was 40 grams exactly.

I very much doubt you'll be able to get that.

Then what we need to do is measure the material's length, width, and height.

And we're gonna do this in centimeters.

Now, in design and technology, we often work in millimeters, so you'll have to convert it to centimeters if all your rulers are in millimeters.

But that's a pretty simple conversion, which I'm sure you can all do.

But it's important that you measure the width, the height, and the length, so you have all three of those.

And in this case, the length of our material is 1.

7 centimeters, the height of the material was 1.

7 centimeters, and yes, the width of the material was 1.

7 centimeters.

Now, this is just my imaginary test piece.

I'm sure yours will be different, but it's the same process that you'll go through.

We then need to calculate the volume and you'll probably know to calculate the volume of a cube, you need to times the length by the width by the height.

So that's important that we do that.

So in this case, we know our length, we know our height, and we know our width.

And what we're gonna do is we're gonna times all them and that gives us a volume of 4.

913 centimeters cubed.

And now we have that, we can calculate our density.

And to calculate the density of an object, the formula is mass divided by volume.

So we know the mass is 40 grams from weighing our material.

And we know that the volume is 4.

913 centimeters cubed.

So when we divide the 40 by 4.

913, we get 8.

14 grams per centimeter cubed.

That is the density of this material.

Quick check for understanding.

Match the term to the definition.

So the terms we have are density, mass, and volume.

And our definitions are: is a measure of how much matter something contains, a measurement of mass per unit volume, and how much 3D space matter occupies.

Pause the video now, have a go at this and come back to me when you've answered it.

So first of all, density.

Well, that is, of course, a measurement of mass per unit volume.

Mass is a measure of how much matter something contains, and volume is how much 3D space matter occupies.

Well done.

So now your first task, and this is your first test.

Select three pieces of material from around your classroom and calculate their density.

Now, if you can find something that is easy to measure the volume, so it's got a length, a width, and a height, that will make your life a lot easier.

And then what you're gonna do is you're gonna write down your results in a table.

And you can see I've used my imaginary example, which was brass.

The mass was 40 grams. I've calculated the volume and then I've done my density calculation using that formula to work out the density.

So you need to do the same for all three of your test pieces.

Pause the video now, have a go at this and come back to me when you filled out your table.

So how did you get on? Well, in my imaginary world, I did brass, steel, and aluminum.

Now, the masses were all the same.

Now, unless you purposely bought in test pieces, I very much doubt that will be the same.

But what you can see here is you can see that brass is quite obviously the dense material here, this has the most density, and aluminum is obviously the least dense material as well.

You can see that from our density calculations.

Now, what is also interesting from this is you can look at the volume.

So in order for our aluminum to have the same mass as brass, you can see the volume was almost three times bigger.

Now, your results will probably look vastly different to mine, but I'm sure you will still have the kind of same density outcomes that I got depending on the materials that you used.

Well done with that task.

So we're now onto our second learning cycle, which is all about absorbency, so let's get going.

So absorbency is the ability of a material to soak up liquids.

Textiles such as cotton have a high absorbency.

They draw up liquids and moisture within the material.

That's what they're designed to do.

If you think about the function of a towel, it's to dry us.

It's to take that moisture, that water from our bodies and put it into the towel, so that means it's got a high absorbency, whereas other materials such as polymers like polyethylene have a low absorbency.

And, of course, this bottle of water, there's not much point if this bottle of water had a high absorbency 'cause we wouldn't have any water to drink from it.

Now, once again, we can carry out a test to measure a material's absorbency.

Quick check for understanding.

Which material would be the most absorbent out of these three? We have wool, we have steel, and we have pine.

Which one do you think is gonna be the most absorbent? Pause the video now, have a think about this and come back to me when you've answered.

It is, of course, wool that's probably gonna have the most absorbency.

So to measure a material's absorbency, first of all, we need to weigh the material in grams. That's the first thing we need to do.

And in this case, the material is 12 grams exactly.

We then need to fill a measuring jug with water.

And then we're gonna place the material into the water for two minutes.

Now, it's important that you use a standard time for this.

So I've used two minutes.

You might wanna use a little bit less than that or a little bit more than that, it's up to you, but use the same time for every material in the test.

What we're then gonna do is we're gonna remove the material and let the excess water drain from that.

So we're gonna leave it for about 30 seconds.

And again, that's gotta be standardized.

So make sure you leave every material for the same amount of time.

Then what we're gonna do is we're gonna weigh the material again in grams. And again, we'll then obviously get a readout and make sure you write that down.

And in this case, it was 26 grams. So you can see the weight of the material, the mass of the material has increased.

What we're then gonna do is calculate the absorbency.

And we're gonna do this by taking the wet weight, sorry, taking the dry weight away from the wet weight.

So we had 26 grams minus 12 grams. So we know 14 grams of water has been absorbed by this material.

So we're now onto your second test.

I want you to select three pieces of material from around your classroom and calculate their absorbency.

Now, textiles on the whole work quite well, not all textiles, but most textiles will have some kind of absorbency.

So they work quite well for this test.

Write your results down in a table.

So we've got the material and then obviously we've got the absorbency in grams. And remember the formula to work that out is the dry weight, take that away from the wet weight.

Pause the video now, have a go at this and come back to me when you've completed it.

So how did you get on? Well, your results might look like this.

So my test pieces were cotton, polyester, and wool.

And you can see from this, the wool had the highest absorbency and the polyester had the lowest.

And that's probably what I would've predicted with polyester being a polymer and the other two being natural textiles.

Well done with that task.

So we're now onto your third test and this is all about electrical conductivity.

Electrical conductivity is the ability of a material to allow electricity to flow through it.

If we take copper as an example, this is a conductor.

It allows electricity to pass through it.

This means it has low resistance.

We then also have PVC.

This is known as an insulator.

It does not allow electricity to pass through it or it lets very little electricity to pass through it.

This means it has a high resistance.

Quick check from understanding.

If electricity cannot flow through a material, the material is called what? A, a conductor? B, a power source? C, an insulator? Or D, a power blocker? Pause the video now, have a go at this and come back to me when you've got your answer.

It is, of course, C, an insulator.

Well done.

To test a material's electrical conductivity, we need to build a simple circuit.

Now, I have done this virtually.

You are gonna do this in the real world.

So all I've got here is I've got a bulb.

You could use an LED and a resistor if you wanted to.

Some jump wires and two AA cells.

The wires are made of copper, which is, of course, a conductor.

So the bulb will emit light when the circuit is in this format.

What we're gonna do is we're actually gonna break that circuit.

We're gonna use jump wires to break the circuit, and we're gonna connect those jump wires to a test piece of material.

And you can see they've got the test piece there.

Now, once we connect the test piece, if the bulb emits light, we've obviously completed the circuit.

And that, of course, means that the test material is a conductor.

It's allowing electricity to flow through it.

If, of course, the bulb does not emit light, then it means that the test piece is an insulator.

It's not allowing electricity to pass through it.

Now, what you can also do when you're doing this test is you can look at the brightness of the bulb.

If the bulb is as bright as it was when you had the completed circuit with just the jump wires, you can assume that the material is a good conductor.

If it's very faint, then it is still allowing electricity to flow, but it has a higher resistance than the copper wire.

So now onto your final task, and this is your final test as well.

I would like you to build a simple circuit, test the following materials to see if they are conductors or insulators.

So we have a steel paperclip, a wooden spoon, which is probably made of beech, a plastic straw, probably made of PVC, aluminum foil, and a steel rule.

Now, if you don't have any of those products, just use something that is similar.

Record your results in a table.

Pause the video now and come back to me when you've completed this test.

So your test results might look something similar to this.

So first of all, we had the paperclip.

Well yes, of course, the bulb did emit light, so it is a conductor, probably made of steel.

Then the wooden spoon, possibly made beech, no, no light was emitted, so it is an insulator.

The plastic straw, probably made of PVC, also no light was emitted from the bulb, so it is an insulator.

The aluminum foil and the steel, yes, the bulb emitted light for both of those, so they are both conductors.

So yours should look something like that.

Well done.

So that brings us to the end of today's lesson.

I hope you enjoyed carrying out all those tests.

Let's have a quick summary.

The physical properties of materials can be tested.

A material's density can be calculated by comparing its mass and volume.

A material's absorbency can be measured by taking the dry weight away from the wet weight.

Electrical conductivity of materials can be tested using simple circuits.

This can show whether a material is a conductor or an insulator.

Well done today.

I look forward to seeing you all next time.

Goodbye.