Hello, scientists.

My name is Mr. Wilshire.

In this lesson, we're going to be looking at multiple shadows, so let's get into it.

Our outcome for today's lesson is to investigate the number of shadows that can be cast by an object.

As always, there are some key words for us to link to the learning as we go through.

I'll say some of the words and I'd like you to repeat them after me.

The first word is light source, fire, torch, cast, evidence.

Great job.

I wonder if you've heard some of those words before and know what they mean.

Well, let's have a little look through.

So first up, something that is a light source produces its own light.

To get a fire going, you need fuel, air, and heat.

It's known as the fire triangle.

If you take one of those things away, then the fire will go out.

A torch is a handheld light that could be powered by batteries, or it could even have a burning flame.

To cast a shadow is to block some light and then cause a shadow.

Evidence is some further information which helps us to prove that something is true or not true.

Let's take a look at the first part of this lesson.

We're gonna be having a look at everyday lighting.

Now, humans have used light sources to make their lives easier since ancient times.

At first, the sun was the only source of light that the earth and its early inhabitants could really see and really use.

Later on, our ancestors then discovered how to control fire and fire-based light sources have then been used ever since by humans.

Can you imagine that? Sitting somewhere that you couldn't light because you didn't understand how fire worked and waiting, waiting desperately for the sun to come up so that you could see things again? Early humans began with fires on the ground, which were used for heating, cooking, and also providing light.

Later on, they made torches from burning sticks and animal fat, allowing them to carry light sources with them wherever they went.

You can see a ancient human with a early type of torch there.

Now modern torches are still handheld light sources, but they're powered by batteries instead, aren't they? More recently, oil lamps and candles were used as human's main light sources.

With early oil lamps, a wick made of plant material was dipped into the container of oil or fat and then lit to create a flame.

With candles, the wick is held within solid wax and lit to provide a light.

Now, early humans found out that they could use some of this animal fat to keep torches going for longer.

So you can imagine that they'd be very happy to be able to carry around a stick and some animal parts that they could then make their own fires with.

So let's have a think.

Which of these light sources were used in the past in order to make things a little bit easier? Was it torches made of sticks, head torches, or lamps using oil and fat? Have a chat with your learning partner.

Pause the video and restart when you want to know the answer.

Hopefully you had a good discussion with your partner there about what you think the answer could be.

Well, head torches weren't really around in the past to make life easier.

So the answers are quite clear here.

Torches made of sticks and lamps using oil and fat.

So torches and sticks to begin with.

And then humans found out that they could really use some animal fat to start burning things for a little bit longer.

And then of course, progressing from that into storing it in a lamp.

So at the end of the 19th century, it marked the rise of the electric light source.

Light bulbs like this one here produced light when electricity is passed through a thin piece of metal, it's called a filament.

The metal heats up and glows and this produces light.

You can see a light bulb there, but some bulbs come in all sorts of different shapes and sizes.

Nowadays though, there are all sorts of human made electric light sources.

You can see a handheld torch there.

You can get those in most shops.

They can even be really, really small.

A head torch, which is really useful if you're somewhere that you need to be able to use your hands to climb, like down in a cave.

A torch on a mobile phone is used to take some pictures, but you can also use it to find your way.

And of course, there's some LED lights for decoration.

And the invention of LED has meant that things no longer get as hot as they used to.

You used to need to have a lot of heat in order to make a light bulb glow.

But as we progressed and we've found out different technologies, we've been able to use LED to make things a little bit easier and also much more energy efficient.

Light sources come in many shapes and sizes.

An electric candle, for example, can help to light your way or be used as some scenery instead of using fire.

A nightlight is where you might cover up a light source in order to change the colour or change the shape.

And then a ring light used for makeup and photos.

Ring lights are really handy pieces of equipment because you can change the type of light that you're going to get.

If you have seen on different social media platforms, you might have seen people use a ring light a little bit like this, and they're able to change the colour of it depending on the mood that you want to set.

So to be like a whitey blue colour or a clear, maybe a bit more orange to give you a bit more skin tone.

So ring lights and LED lights like this are really, really handy when you're trying to create some sort of atmosphere or mood.

After dark, modern cities are lit up by thousands of light sources.

Scientists and engineers design and invent ways for us to use light to achieve different effects.

And over time, engineers have designed light sources which are brighter and which are more efficient than early lights that we've used.

I can see in the picture there that there's lots of different types of lights.

There's lights inside the buildings.

There's lights on top of the buildings, so you can see some of the things on the outside or to make it decorative.

There's also some lights down in the bay there as well.

Different colour lights as well, marking the edge of the water.

Now, everyday lighting.

You might have seen something a little bit like this before, especially if you visited any sort of stadium for a sports event.

You may have also visited a stadium for different music events as well.

But flood lights will allow people to play and watch sports at night.

And of course, lasers can be used to create patterns in the sky and also on buildings.

There are some fantastic projectors that you can get that you can project whole images on and change the face of the building.

Specialist light sources like those projectors can help people create some kind of special effects.

Photographers use powerful lights like these, and they're not just using the umbrellas there because they're worried that it's going to rain in indoors.

They've actually got lights inside the umbrellas that are aimed away from the person who's doing the presenting or the person who is having their picture taken.

The umbrellas are filled with a silvery material that allows the flash to go off and then cover a wider area, rather than just having a single torch shining a light in a single location.

You can also see lots of other types of lights all around the studio as well.

So you can create some all-encompassing sort of light.

You may have been to the theatre or a concert and see some different colour lights as well.

These lights can move as well as change colour.

So if a follow spot were following the actor or the main singer on the stage, you'd be able to see them wherever they went.

So let's have a think then.

What are some ways that scientists and engineers use lights to achieve different effects? Pause the video now and have a think.

Hopefully you've had a good chat and discussion about that.

And let's have a look at the answer.

Well, it can be two possible answers here.

They can design lights, which create atmosphere, and they also design lights that are more powerful.

Second thing, then, which of these are examples of light sources designed by an engineer? Pause the video and have a discussion.

Hopefully you came up with some good answers there.

Let's see what the answer is.

Again, two possible answers.

Now, sunlight isn't something that an engineer or a scientist has created.

That's natural light up in the sky, isn't it? So floodlights at a tennis court or ring lights used for makeup and photography.

So let's get onto our first task in this lesson.

First part here says make a list of the different light sources that you use in one day.

That's a really good thing to think about, isn't it? I wonder what different lights I've used in my day.

Second part of this is to invent a new light source that would be helpful in your life or in the life of someone that you know.

You can record your design with a label diagram.

I wonder what kind of things I might need to use light for and what's gonna make my life a little bit easier.

I can see that Jun here has, he wants to create a light to help him find things at the back of his cupboard.

I wonder what kind of light would help him there.

And Andeep has an idea for helping his dad walk his dog safely at night.

Yeah, in both of those situations, you don't really want to be holding a torch while you're trying to find your things or walk your dog.

Pause the video, have a go at the task, and then replay when you're ready to start again.

I wonder how you got on.

Hopefully the discussions that you've had have been really fantastic.

Let's have a look at some of the possible answers that you could have come up with here.

The first part here, you might have looked at your light on a clock when your alarm went off if you have one of those.

You might have used some lights in the house as you got up.

If it was dark in the winter, for example.

You may have even opened the fridge to get something and the light went off in there.

That's a good point.

Kind of forget that there's a light inside a fridge.

Maybe you used a light in a cupboard at school to find something or played a game on your phone or watched some TV.

Both of those things use an LED screen.

So there's always has to be a backlight lighting things up so you can see them.

Maybe you even took a photo with a phone and it had a flash on it, or you used a torch under a duvet to read secretly at night.

Second part of this says to invent a light source.

Now I can see that Andeep here has, well, he's created some sort of wristband torch there, which is quite good, isn't it? Because wherever his hand is going to be pointing, it's going to be able to see the dog.

The light is attached to a wristband, so dad can point it where he wants to see without letting go of the dog's lead.

Handheld light sources are really useful, but if you need to use both of your hands, having something that you can attach it to is really useful as well.

Let's get into the second part of the lesson then, and have a look at multiple shadows.

Jacob and Sofia have made some observations here about different light sources that they've seen in real life.

Sofia says that she went to watch a play at the theatre, and the objects on stage cast more than one shadow.

Jacob says that when he went to watch football in the daytime, all the players had a shadow.

But at nighttime, under floodlights, they, well, each player had four shadows.

So how can one object or person cast more than one shadow? Let's get into it.

Well, when more than one light source is used, more than one shadow can be cast by the same object.

So when Sofia went to the theatre here, for example, there were two spotlights.

Each of these spotlights led to a different shadow being cast by the same object.

You can see the box there has a shadow from spotlight one, and then spotlight two cast a shadow over there.

So you can see that by having two different light sources, two shadows are created.

So when Sofia went to a music concert, there were lots of spotlights.

So having multiple spotlights then led to multiple shadows being cast.

You can see here that the box has loads of different shadows.

Sofia is not really sure how many there were.

If you were a lighting engineer, it would be your job to try and get rid of those shadows by placing lights in different places.

When Jacob watches football during the day, the sun is the only light source, and so the player casts one shadow.

But at nighttime, in a floodlit football stadium, well, each player is lit by more than one light source, and you can see all the spotlights up in the roof there.

So that means that multiple shadows are being cast.

So I wonder what you think will happen to the number of shadows cast here.

Is this true or false? When more than one light is used, more than one shadow can be cast by one object.

Pause the video here and decide is that true or false? Then justify your answer using one of the statements below.

Okay, what do you think? It was true.

When more than one light is used, more than one shadow can be cast by an object.

And if we were to try and justify our answer, we know that there, well, one object could block more than one beam of light.

Now that causes multiple shadows, especially if the lights are all in different locations.

So this leads Jacob to think of a question.

How does the number of light sources affect the number of shadows one object can cast? Sofia has an idea.

She wonders if the number of shadows is equal to the number of light sources.

Maybe.

I don't know.

Wonder how they could investigate this.

Have a quick discussion and then we'll move on.

It's important to have those kind of discussions, even if you all kind of know what the answer is.

Scientists can gather evidence to answer questions and support their ideas.

So they have to plan investigations to help them to do this.

Jacob and Sofia want to gather evidence to answer Jacob's question and to see if Sofia's idea is correct.

There's two different things here that they need to look into.

He asks how the number of light sources affect the number of shadows one object can cast, and Sofia asks, I wonder if the number of shadows is equal to the number of light sources.

Jacob and Sofia then decide to shine a torch on a can in a dark room.

That way they're going to be able to see the shadows really easily.

They'll see whether they're able to cast more than one shadow using just one torch and one can.

Then they're gonna add a second torch to see how many shadows that they're able to produce.

They'll explore this using as many torches as they can find.

I wonder how many torches they have and what they're going to be able to find.

So why do scientists gather evidence? Pause the video and have a chat.

Well, scientists need to have these discussions because they need to answer the questions.

If nobody knows the answer to the question, then nobody gets anywhere.

It can also help them to support their ideas so they can prove it to other people.

So here's part one of this task.

Try to answer Jacob's question by exploring shadows and light sources.

Remember he said, how does the number of light sources affect the number of shadows that one object can cast? And Sofia asked, she wonders if the number of shadows is equal to the number of light sources.

So explore how many shadows that you can cast from one object using just one torch.

Add a second torch and repeat your exploration.

Continue to add torches until you've gathered enough evidence to answer the question and the idea.

Make sure that you discuss these ideas with each other as well.

You might have all different ideas as to how this turned out.

Pause the video here and we'll go through some of the answers afterwards.

Well, I wonder how you got on.

Hopefully you had a good time doing that experiment and having some fun, making some shadows as well.

I wonder though, if you found the same thing as Jacob here.

When we had one torch and one object, we could only cast one shadow.

We tried different objects and different torches, and when we had two, we could make two shadows with one object.

And when we had three torches, we could make three shadows.

Did you find the same thing as Jacob there or not? Is the number of shadows equal to the number of light sources? Jacob and Sofia are correct.

Each object can cast one shadow for each light source that is shining on it.

So did you find the same thing as Sofia? Our evidence supported my idea that the maximum number of light sources is equal to the maximum possible number of shadows.

We did find that you could make fewer shadows than light sources if you shone all the torches from the same place.

Yeah, that's right, isn't it? Because if all the torches are in one place, that's just gonna create one big light beam.

The second part of this task says, which of the pairs of images below provides evidence to support the ideas that the number of light sources affects the number of shadows? Is it A, B, or C? Have a discussion.

Pause the video here and continue when you're ready.

Well, I wonder if you found the same as these answers here.

C.

You can see there that the torches are shining onto the can and creating two shadows.

And at the bottom there, one torch is creating one shadow.

In B, there should be a third shadow in the middle of the top one there and in A, well, there's only one shadow, isn't it? I don't think that matches up what you found as well.

So let's summarise our learning, shall we? Humans have used light sources to make their lives easier since ancient times.

Scientists and engineers invent and design ways for us to use light to achieve different effects.

When more than one light is used, more than one shadow can be cast by one object.

And scientists need to gather evidence to answer questions and support their ideas.

Hopefully, you've enjoyed using some different light sources to create some shadows as well during this lesson, and I hope that it inspires you to do some of your own investigating and exploring and answering some of your own questions about light and shadow.

I've been Mr. Wilshire, and I look forward to seeing you again another time.