Bitesize Science

I'm Jon Chase, and I'm a scientist.

Science is everywhere.

Science is amazing!

In the next 60 minutes,

I'm going to show you my top 20 science demos.

Oh, that's warm!

Kicking off at number 20 is osmosis.

Big shout to the students at Copthall School

for throwing stuff at me.

All life needs water.

Water moves in and out of living cells across their cell membranes.

These membranes are partially

or selectively permeable.

Check which term you need to use.

Osmosis is a special type of diffusion

which happens across a membrane, always in regards to water.

The hockey net represents the membrane.

You have some water molecules.

The blue balls represent water molecules

and the other colours are different-sized solute molecules

which are dissolved in the water.

I want you to send different-sized molecules

at this membrane

and see what happens.

The net only lets the smaller blue balls through

and this is what happens in osmosis.

When water molecules move from a high water concentration

to a low water concentration across a membrane,

the process is called osmosis.

Water molecules actually move

back and forth across the membrane all the time.

But overall, there is a movement of water

from an area of higher water concentration

to an area of lower water concentration.

The overall movement is called the net flow. Get it?

I feel a rap coming on.

Plants use osmosis to take in water through their roots.

The net flow of water into the plant causes the plant cells to expand

so they become turgid or stiff.

This means they are able to hold the plant upright.

However, for animal cells, osmosis can cause problems

as animal cells have no cell wall, and there is a danger

they may take in so much water that they explode.

This is called lysis.

There is also a danger

that so much water moves out

that they become irreparably damaged, like this blood cell.

When this happens, this is known as crenation.

Our bodies stop this from happening

by carefully regulating the concentration of our tissue fluid.

It's complicated stuff, so how about another rap to help clear things up?

So, bottom line - Osmosis is the net movement of water

from an area of high water concentration

to one of lower water concentration

across a selectively or partially permeable membrane.

And now, the race is on.

Racing chemicals - rates of reactions at number 19.

Chemical reactions are all about collisions between particles

and the rate of reaction depends on how frequently particles collide

and with how much energy.

There are four methods of increasing the rate of reaction.

My mate Professor Sella is going to talk me through them.

First up - concentration.

What we're going to do is set up these three reactions.

This one's going to be the high concentration one.

You can see there's more stuff in it.

We're going to put a medium one, and then finally

we'll have a low concentration one down at the other side.

This is going to be like a race.

We're going to start them off

and when we get to the end of the race,

the solution is going to turn blue.

-Are you ready?

-Yeah.

-Steady, go!

And now, let's just mix them up.

'The reaction in the beaker finishes with the sudden release of iodine

'which interacts with the starch that is already present

'to turn the solution blue almost instantly.'

We have the reaction going

and we're waiting for those racers to get to the end.

Firm favourite is High Concentration.

Also in the running is Medium Concentration.

Bringing up the rear is Low Concentration.

Whoa! There went the first!

As expected, the firm favourite,

High Concentration, comes storming through the finish line.

Now, what about this one?

I'm wondering if that one's going to go.

-What?

-There went the second one.

The runners are coming in exactly in the order that we were expecting.

And that one, he's been out of training or something.

I wouldn't bet on that guy.

That's not... Ooh! There it went.

Of the three solutions added,

it was the solution with the highest concentration

that resulted in the quickest reaction.

Because the reactant particles are more crowded,

collisions take place more frequently.

So that was concentration.

Now onto temperature.

When the temperature is increased,

the particles in the solution move more quickly.

This increases the frequency of collisions

and the energy with which they hit each other.

We're going to see how temperature affects the rate of reaction.

We'll do that by using a glow stick which reacts when we break it.

Now let's see what would happen if we cooled it down.

So as you can see, the reaction gives off light

but this isn't giving off light

so the reaction appears to have slowed down.

If we cool it down and the reaction slows down,

what happens if we heat it up? Let's give it a go.

A bit of friction to heat it up.

And as we warm up the solution, what happens to the reaction?

Well, it's started to give off light again. Even more light than that,

and because it's now got warmer,

the reaction has sped up.

So we can say that increase in temperature speeds up a reaction

and decrease in a temperature slows down a reaction.

So stick it in your freezer if you want to keep it for tomorrow

to have more raving. Right, I'm off.

Next up are catalysts.

They work by speeding up a reaction and they do this by increasing

the number of successful collisions between particles.

Back to Professor Sella and his great experiments.

Here we have hydrogen peroxide

and I'm going to add a little bit of a solid catalyst.

This is manganese dioxide, tiny bit.

Can you see the tiny little flecks

of manganese dioxide are actually causing the reaction?

They're causing hydrogen peroxide

to decompose to oxygen and water.

So they're reacting and remaining unchanged now?

Absolutely. It's interesting that on this side we have the same hydrogen peroxide, but without the catalyst

and actually, it decomposes very, very slowly.

Even if you leave it in the fridge, eventually it will go off.

Let's not mess around, let's give it a real load of catalyst.

Do I have to step back for this?

Well, you'll see. Go!

It's actually gotten so hot

that it's boiling. You can see a plume of water vapour

accompanies the oxygen as it comes out.

The catalyst is causing the breakdown of hydrogen peroxide

into water and oxygen at a phenomenal rate.

But the catalyst has not changed at all throughout this reaction.

The catalyst is still there.

We could pour this all off, we could filter it away

and we would collect all of that black stuff. That's our catalyst.

And finally, the size of particles.

How does that affect the rate of reaction?

Let's burn this sugar lump.

Well, it burns a bit.

As it burns, the sugar is turned into carbon dioxide and water.

What about if we decrease the particle size?

Using something like icing sugar. Using a smaller particle size

increases the surface area.

We've used the same amount of sugar as is in this cube

and we've put it into this tube.

Let's see what happens when we try and burn it this time.

There was a lot more reacting going on, and a lot more heat.

I could even feel it coming off.

'So by breaking down the sugar into a powder,

'its surface area increased.

'More of the sugar has been exposed to the oxygen in the atmosphere

'so collisions can take place more frequently.'

Decreasing the size of the particle increases the rate of reaction

and that's because we have increased the surface area.

So, let's recap.

To increase the rate of a reaction,

the concentration needs to increase

or the temperature needs to increase

or the size of particles needs to decrease.

And the other way to increase the rate of reaction

is to use a catalyst.

At number 18 is mitosis,

explained through the medium of dance - and rap.

Wouldn't it be great if we could clone ourselves?

Well, the cells in our bodies do this all the time

by a process called mitosis.

It is one of the most basic and beautiful processes on the planet.

'It's just like a dance.

'So I've got the pupils here at Copthall School

'to show you how it works.

'So get settled and check out my mitosis rap!'

Mitosis is a type of cell replication

that enables cells to clone themselves.

It's essential to growth and repair.

It's a brilliant, simple cycle that is fundamental to life.

When you see mitosis through a microscope,

it looks like a dance of the chromosomes.

We're looking at a cell with only a few chromosome dancers.

A human cell contains 23 pairs of chromosomes.

The mitosis cycle starts with the chromosomes of the parent cell

making identical copies of themselves, so when the cell divides

there will be identical chromosomes in each dividing half.

Then the doubled chromosomes line up

along the central axis of the cell

and microtubules called spindle fibres pull them apart

to opposite ends of the cell.

Now, each end of the cell has a full set of chromosomes

around which a nucleus forms.

Then the cell membrane pinches in between the two nuclei,

dividing the original cell into two new daughter cells.

The daughter cells are genetically identical to the parent cell.

The parent cell has cloned itself

and the cycle begins again.

Can I have a parent cell, please?

And now some alchemy, as I turn copper into gold.

Well, not exactly, but it's still impressive.

It's electrolysis: electroplating at number 17.

Electrolysis - so what does it mean?

Well, let's split up the word.

Electro - electricity.

Lysis - splitting.

So electrolysis is splitting a substance by means of electricity.

And it's very useful. Electrolysis can be used to plate jewellery.

Ever wondered how gold can be so cheap?

Well, electrolysis can be used for electroplating,

where one metal is coated with another, so it's not solid gold.

But bling ain't my thing, so in this demo

I'll plate a copper coin with zinc from a nail.

'First of all, we need an electrolyte.

'This is a liquid that conducts electricity.

'In this case, we're going to use dilute hydrochloric acid.'

Next, we need a source of electricity.

'I've attached the negative end of the battery to the coin

'and the positive end to the nail.

'Let's see what happens.'

And there it is, a zinc-plated penny.

So how does it work?

The battery causes electrons to be removed from the positive electrode,

which is called the anode.

Electrons are forced by the battery

onto the copper coin,

which is the cathode.

At the anode, two electrons are removed from each zinc atom,

turning them into positively-charged zinc ions.

These zinc ions are attracted to the negatively-charged cathode,

where they gain electrons.

This turns the zinc ions back into zinc atoms,

which explains why the copper coin

is coated with a layer of zinc.

And that's how the coin becomes zinc-plated.

Right. I'm off to go spend a penny.

Time to look beneath the surface,

with microscopy at number 16.

We can see objects as small as 0.1 millimetres

and that means we can just about see these lice eggs in our hair

and tiny single-celled organisms like amoeba,

but it's possible to see things much smaller than that

if we use magnification.

There's three types of microscope - light, like this one here

and two types of electron microscope

like those ones over there.

'Light microscopes use light and mirrors

'and can see things as small as 400 nanometres.'

This allows us to get down to the world of the cell

and that means some pretty amazing things can be seen.

Here's an amoeba engulfing red blood cells

and red and white blood cells moving through a tiny blood vessel.

And human sperm.

A leaf surface at 600 times magnification

and the head of a dog tapeworm no bigger than a grain of rice.

Plant cells crammed with chloroplasts.

Look at these glucose crystals.

But light microscopes have a limit.

Any object that's smaller than the wavelength of light

appears blurred. But in the 1930s,

a new kind of microscope was invented,

which took our eyes further than they'd ever been before,

to places we'd never seen before - the electron microscope.

The specimen is put in a vacuum

and is viewed not by light waves

but by a single beam of electrons

that scans the surface, building up an image on a screen

rather like a television picture.

Because electrons have a wavelength 100,000 times smaller than light,

electron microscopes can magnify objects up to 10 million times.

There are two types of electron microscope - the transmission

and the scanning.

The scanning electron microscope scatters electrons

across the surface of a specimen. It can magnify in incredible detail.

This is a leaf surface under a scanning electron microscope.

Both types of electron microscopes make black-and-white images

but these have been colourised to make them clearer

and a lot more appealing to the eye.

Check out this fruit fly.

A pubic louse and its claws.

Cancer cells splitting.

A blood clot.

And human sperm cells on the surface of an egg.

But what about a transmission electron microscope?

The difference with a transmission electron microscope

is that it sees THROUGH things.

It does this by sending beams of electrons

rather than light, through ultra-thin specimens.

Using these microscopes, we're able to study the interior of cells

and their organelles

and we've been able to get a better understanding of how pathogens,

such as viruses, invade cells,

like these HIV particles budding on the surface of a T cell.

Now a new type of electron microscope,

a tunnelling electron microscope,

has even made it possible to see the arrangement of atoms.

Just how far will microscopy go?

Now, throwing yourself out of a plane may not be your idea of fun

but if it's all in the name of science...

At number 15, falling bodies.

Aaagh!

Science is always evolving.

About 2,000 years ago, this guy here, Aristotle,

said the rate of acceleration with which a body falls to the ground

depends on its mass.

Look at these bodies falling.

Why have some accelerated to a greater speed then others?

If Aristotle was right and acceleration depends on mass,

this would mean a heavier body

would drop at a different acceleration to a lighter body.

So, let's give it a try.

At ground level, we have Jessica with a camera

to record the exact point when the ball hits the ground.

Hello, girls. Right, to the left, we have a cricket ball

and that's three times greater mass than the tennis ball,

so let's drop them at the same time and see what happens.

OK, are you ready? Three,

two, one,

drop!

How did it look, Jessica?

-They looked like they dropped at the same time.

-Wicked.

Looking at Jessica's footage, it looks like the balls do indeed

hit the ground at the same time,

even though the cricket ball

is three times heavier than the tennis ball.

So our experiment shows that Aristotle was wrong.

The balls drop at the same rate, regardless of their mass.

The first person to point this out was Galileo,

who according to legend, did the same experiment

from the Tower of Pisa 500 years ago.

So if the balls landed at the same time,

the same should be true of a hammer and a feather, right?

Well, let's give it a shot.

Three, two, one.

What happened there?

Air resistance affects the feather - that's why it falls less quickly.

That's right, it is air resistance!

Air resistance is stopping the feather from falling

to the ground at the same rate as the hammer.

Remember our skydivers?

They're able to change their rate of acceleration

by making themselves more or less streamlined.

If we remove the effect of air resistance, all falling bodies

should fall at the same rate, regardless of their mass.

So let's go to a place where

we can try this experiment with no air resistance -

does anyone know a good place where we could do that?

-In space!

-Yes! A vacuum in space!

During the fourth moon landing,

Galileo's theory was put to the test.

'Here in my left hand I have a feather -

'in my right hand, a hammer.

'And I guess one of the reasons we got here today

'was because of a gentleman named Galileo

'a long time ago, who made a rather significant discovery

'about falling objects and gravity fields.

'And we thought, where would be a better place

'to confirm his findings than on the moon?

'I'll drop the two of them here, and hopefully they'll

'hit the ground at the same time...

'How about that?

'That means that Mr Galileo was correct - and his findings...'

The feather and the hammer land at the same time.

Unlike Earth, the moon has no atmosphere

so there's no air resistance to interfere with the experiment.

The moon's gravity causes them to fall with the same acceleration -

even though they have very different masses.

It's a shame Galileo wasn't around to see that.

And for my next trick, I will make money disappear!

Easier than it looks!

For this experiment, I'm going to show you

a disappearing act, with the help of just a coin and a glass of water.

Here we have one coin - simply take a glass,

stick it over the top!

To make the coin disappear, we add a bit of water.

And hey, presto!

The question is, why does the coin disappear?

From the top, you can see the coin is still there,

but from the side, the coin isn't visible.

When there's no water in the glass, light from the coin travels

through the glass to our eyes at a particular angle.

When water's added, the light from the coin hits

the inside of the glass at an angle that's greater

than what is known as the critical angle.

Once this happens, all the light from the coin

is totally internally reflected,

and it can only escape through the top of the glass.

Here's another cool trick that uses total internal reflection.

I've created a stream of water by making a hole in this bottle.

If I shine the laser in the right place,

the laser hits the opening of the hole

and it travels down the actual beam of water.

The light is being totally internally reflected,

and trapped within the water.

Lasers in experiments should always be clamped

or stable on a bench,

as they can be dangerous if they shine into anyone's eyes.

In this fibre-optic lamp, light enters one end of the fibre

just like the light from the laser entering the stream of water,

and this is reflected repeatedly until it emerges at the other end.

Optical fibres have revolutionised the way we communicate,

carrying data as pulses of light over incredible distances

and creating the information superhighway.

It's time to heat things up a little on a cold day in Scotland...

Number 13 - endothermic and exothermic reactions.

We all know that some chemical reactions

release energy in the form of heat.

But what about reactions that do the opposite?

I'm at this shopping centre in Edinburgh on a chilly Saturday

to demonstrate endothermic and exothermic processes.

-Are your hands cold?

-Yeah.

-Aye.

-And you've heard of these, haven't you, hand-warmers?

-No!

You haven't heard of a hand-warmer? You haven't seen these?

When your hands are cold, crack this inside

and this makes your hands warm.

-You've all seen water turn into ice, yeah?

-Yeah.

This is going to turn into something that will seem like ice,

it will go crystalline, but it will get hot. I'm going to cut it open...

-Bang!

-LAUGHTER

Right, here we go. I'm going to pour it into here...

-You know that that was pretty cold when you touched it, yeah?

-Yeah.

-Right... You want to touch it underneath? Cold?

-Yeah, that's cold.

We need something to kick it off,

for it to give off heat to warm your hands.

-So we're going to stick something in it.

-Fire!

-Right...

-Oh, what are you doing?

-Oh...!

Oh, that's warm!

It's getting warm, is it?! But I thought you said it was cold?!

'What is happening here? The blue liquid is actually a super-saturated

'solution of sodium ethanoate.

'The liquid is so full of sodium ethanoate

'that it's very close to becoming a solid.

'I just have to put in this wooden stick

'to start off the process, and the liquid turns into a crystal.

'Because it releases energy, we call it an exothermic process.

'It's easy to remember, because energy "exits".

'Some chemical processes actually absorb energy. Check this out...'

What I'm going to do is, I'm going to try to get this to stick to that.

-Stick to the plank of wood?

-You need glue.

Glue? You could use glue.

Has anyone ever been in a really cold place

and it says, "Don't lick the pole?"

Don't do it. You go skiing, and you get stuck to it, and that's

your holiday finished because your tongue's stuck to this pole.

We're going to do the same thing with that.

So I'll grab some of this.

All right, now, put that lid back on.

So, you put in some of that.

Now, mix it together. See that smell? Really smelly...?

-That's what ammonia is.

-That's Thomas's feet!

-Oh!

-I can't smell it myself.

'The ammonium is a by-product of the reaction taking place in the beaker.

'For this reaction to take place at room temperature,

'energy must be absorbed from the surroundings in the form of heat.

'So much heat is being absorbed

'that it's freezing the water underneath the beaker.

'This is an endothermic reaction.'

Heat is taken from the surroundings and goes into it, so it's

"indo-thermic" or endothermic - that's how I remember it.

Endo's like indo and exo is like, well, exit!

OK, could someone hold this beaker please?

Huh?!

This has taken all of the heat out of the water and cooled it down.

It's cold, isn't it? Right, so, let me break that off...

You can't get it off!

When you take heat from water, it gets cold

and it turns into ice -

and that...was an endothermic reaction.

How do you know that's not long-lasting glue?

It's water.

More magic now - making the handle of a Pyrex kitchen jug disappear.

You never know - might come in handy some day...maybe!

The power of invisibility -

it's not just the stuff of science fiction and superheroes.

It's a reality! This is the handle of a Pyrex jug.

It's perfectly visible, right?

But watch what happens when I add some vegetable oil...

Woah! The handle's disappeared!

The reason this happens is because light refracts.

Light moves at different speeds through different substances,

and this speed is measured by something called refractive index.

When light travels through two substances

with different refractive indexes,

it changes direction at the boundary between the two substances,

if it's travelling at an angle.

This can be seen here by shining a light through a glass block.

This change in direction is called refraction.

Refraction makes looking at objects under water quite tricky,

since water and air have different refractive indexes.

The light from objects under water

changes direction when it leaves the water,

making them appear in a different place to where they actually are.

Diving birds have to make this adjustment when looking for fish.

An object is only visible if it reflects or refracts light.

When the glass is empty, the handle of the jug is visible because

the air in the glass has a different refractive index to the Pyrex.

But the vegetable oil has a similar refractive index to the Pyrex.

When we add oil to the glass, the light leaving the handle

no longer refracts, and hey, presto, the handle disappears!

Ever wondered what your liver was for? Worth looking after it!

Enzymes!

There are tens of thousands of chemical reactions

going on inside our bodies all the time. I'm at a farmers' market

in Edinburgh to show people how enzymes contained in an animal liver

can help turn a dangerous chemical like hydrogen peroxide

into something totally safe.

Welcome to the wonderful world of enzymes!

Do you know what your liver's good for?

-Not really.

-What your liver's good for...

is for breaking down stuff.

-I'm going to show you how that works.

-OK.

First, I'm going to take some of this stuff.

Put on my safety goggles...

Hydrogen peroxide - you can use it

to bleach your hair if you like, to look pretty!

When you eat stuff,

your body breaks it down, but it can produce some harmful chemicals,

and this is one of them.

Because it's the detox organ in the body, the liver is full of enzymes

that work as catalysts to speed up the breakdown of harmful chemicals.

Catalysts speed up chemical reactions

without being used up or chemically changed.

Enzymes speed up reactions - they make things happen quicker.

'In our bodies, hydrogen peroxide is broken down

'by the enzyme called catalase.'

Sorry, I don't do liver - I just, I don't like it.

'What happens when the catalase in liver

'comes into contact with hydrogen peroxide?

'I've added some blue washing-up liquid,

'which shows you the gases more clearly.'

Liver is effective at breaking down the hydrogen peroxide.

'And it does this by breaking it down into water and oxygen.'

That is what we call an enzyme reaction,

and it's caused by catalase in our liver. Thank you!

Hydrogen peroxide has the molecular structure H202.

Catalase splits it up into H20 and 02 - water and oxygen -

but how does it work?

Every enzyme has a place in which the molecule fits exactly.

This is known as the active site.

The active site of the catalase

allows the hydrogen peroxide molecule to fit exactly.

You could say the active site is like the ring of a bottle opener.

The hydrogen peroxide molecule slots exactly into the active site,

and it's that that splits up the molecule into oxygen and water -

breaking up the dangerous hydrogen peroxide and making it safe.

Good stuff, that liver!

Time to inflict senseless violence on a defenceless jelly baby,

to learn about...food as fuel!

All living things are in an energy race.

We have to keep getting enough food to fuel our bodies.

But not quite this much!

The food industry uses the word calories to describe

how much energy is contained in food.

But scientists prefer to use the word joules -

let's see how many joules are in this jelly baby.

Our body uses food like a steam train uses coal.

As we break down our food, it releases the energy our body needs.

This is respiration, and it happens in our cells.

We can look at how this works in the lab, by reacting our food

with potassium chlorate, a powerful oxidising agent.

According to the packet, one jelly baby contains 90 kilojoules.

Let's see what 90 kilojoules of energy looks like

when we release it in 10 seconds.

So, let's give it a go...

90,000 joules released in 10 seconds.

'A reaction similar to this is going on inside our own bodies

'when we eat a jelly baby - just a lot slower and a lot less intense.

'The cells in our bodies release the energy from the jelly baby

'by combining it with oxygen that we breathe.

'This is aerobic respiration.

'Aerobic respiration is a chemical reaction.

'If you've ever wondered how we calculate how many calories

'there is in food, it's probably because someone somewhere

'has been burning it and measuring the joules of energy released.

'If every jelly baby has 90 kilojoules, this means

'there's a lot of energy in this trolley, which is a good thing...'

..considering we need about 11,000 kilojoules a day.

Do you remember that guy who had an apple fall on his head?

Lies! He only saw it fall! Isaac Newton and his 1st Law.

Ever since we invented the wheel,

humans have been moving around faster and faster.

More than 300 years ago, a guy called Isaac Newton

came up with three laws about how things move.

The first law is that a body will continue in a state of rest

or uniform unaccelerated motion

unless acted upon by some external force.

So what's that all about?

For a body to be at rest, the forces need to be balanced.

Here, the boarders are trying to be at a state of rest.

Some of them are better than others!

When they DO manage it, their forces are balanced.

The weight of the boarder is balanced

against the force acting up through the board.

So we've seen bodies at rest, but what exactly happens

when a body is in motion? Well, the forces are still in balance.

To go at a constant velocity, the force from the boarder's leg

must balance the opposing forces of friction and air resistance.

Here, the skater is moving at a constant velocity.

The force from his legs is balanced against the forces of air resistance

and the friction from the ice.

Because there is no force of gravity on this ball in space,

it continues in a perfectly straight line until it hits a wall.

If forces are not balanced, the velocity will not be constant.

When the boarder stops pushing with his leg,

friction and air resistance win the battle,

and the boarder decelerates.

Equally, when the boarder needs to accelerate to do a trick,

the forces are not balanced - he is applying

a greater force than the opposing friction.

Well, that's what he would like to do anyway!

Force = mass x acceleration. Well, that was easy!

So, onto number seven - yep, you guessed it,

it's Newton's Third Law.

These skateboards are great examples of how things move.

Newton's Third Law states that if a body A exerts a force on a body B,

then B will exert an equal, opposite force on body A.

Body A and body B - better know as Phil and Oli -

can you exert a force on Oli please, Phil?

'This force gives them the same initial acceleration,

'and once they've parted company,

'they move off at the same speed, in opposite directions.'

That's because the force exerted by A

had an equal and opposite reaction.

'When Phil pushes Oli,

'there is an equal and opposite force that pushes Phil back.

'Newton's Second Law states that for any force applied on an object,

'acceleration is inversely proportional to the object's mass.

'So here, because Phil and Oli are roughly the same mass,

'assuming friction is a constant,

'this force provides them with the same initial acceleration,

'making them travel a similar distance from their starting point.

'How would increasing the mass on one board affect acceleration?'

We're going to bring in another skater. Martin, if you can step in?

All right, guys?

'They did both move away, but this time the board with two skaters

'didn't move away with as much initial acceleration

'as the board carrying one skater - so what's happening?'

When Phil pushes against Oli and Martin,

Oli and Martin push back with the same force,

but in the opposite direction.

Remembering Newton's Second Law, their initial acceleration

will be inversely proportional to their mass,

and because Oli and Martin are about twice the mass of Phil,

assuming friction is a constant,

the force can only accelerate Oli and Martin half as much as Phil.

So Phil travels twice the distance in the same time.

This is exactly the same principle that gets rockets into space.

Newton's Third Law can help us to understand

how we can change this plastic bottle into a water rocket.

When I first start pumping, the increasing air pressure

pushing down on the water is being held back by the bung.

But as the pressure increases, eventually it's

too much for the bung, and the water comes out with a huge force.

This is where Newton's Third Law comes in.

The rocket exerts a force on the water, pushing it downwards.

The water exerts an equal but opposite force on the rocket,

pushing it upwards.

This is exactly the same principle that gets rockets into space.

The burning fuel is forced downwards -

it exerts an equal but opposite force on the rocket,

forcing it upwards.

You can solve the biggest problems with small solutions.

And to feed the world, you've got to start with seeds -

it's germination at number six.

Germination is the process by which a plant begins to grow from a seed.

Seeds need certain conditions to germinate successfully.

Doctor Laura Bowden is a seed specialist, and I've asked her

to try and germinate crop seeds for us in different conditions.

Well, these are barley seeds,

and these ones I grew in our controlled temperature room,

which is at 20 degrees, so they've been nice and warm.

These ones have been in the fridge

at four degrees, so they haven't germinated at all,

there's quite a difference, showing that temperature really is

very important to seed germination.

So we've seen that warmth is essential for germination,

but there are two other crucial factors.

Water is probably the most important factor for germination.

Without water, most seeds can't germinate.

In hotter parts of the world, the lack of water is a serious problem.

Droughts can result in crops dying, causing terrible starvation.

This experiment here, these are rye grass seeds.

These ones have had a good amount of water - enough for them to grow well.

These ones here haven't had quite as much water, so they're

looking unhealthier. These poor ones have had no water at all.

If you give them too much water, that would also be

a stress and they wouldn't be able to go cope and it would kill them.

We've seen that warmth and water are essential for germination,

but there is one other crucial factor.

Oxygen is very important. They need oxygen because they have to respire.

Seeds contain a food store. Respiration requires oxygen,

and releases energy from the food store.

This is why seeds need oxygen during germination.

Once the young plant has leaves, it no longer needs its food store

because it makes glucose in its leaves by photosynthesis.

Respiration then releases the energy needed from this glucose.

So these are the basic factors that seeds need to germinate...

But to have any chance at solving the world's food shortages,

scientist are helping farmers work out the best ways

of getting their crops to grow quickly.

Quite often, farmers will apply fertilisers to their fields,

which will speed up germination and plant growth.

So these are grass seeds again,

and these ones have had nitrate added to the solution that they're given

to grow with, and these ones haven't, they've just had water.

And you can see there is a huge difference in the growth.

These ones, they have started to germinate, you can see the shoots,

but they're so much smaller,

and that's because of the effect of nitrates,

which is the major component of fertiliser -

so farmers use exactly this principle.

Wow, that really is impressive.

The research that Dr Bowden and her colleagues are doing

is crucial to understanding how to improve our farming techniques.

In 2011, the world population hit 7 billion,

and by 2050, that number will be 9 billion -

9 billion people need an awful lot of food.

Science is helping us understand more and more

about how plants grow and germinate.

And it's helping us to understand

how we can feed our ever-expanding population.

Get in line for more skateboarding tricks -

putting the "sick" into physics! Time to create some friction!

So now, we're going to talk a bit about friction.

Any time one surface moves over another,

there is a force of friction. Friction is a force

that always acts in the opposite direction to movement.

Here, the force of friction

is opposing the motion of the skateboard.

We spend a whole lot of time battling with friction.

Friction can be a surprisingly strong force.

Try this next experiment for yourself -

fan the pages of two books together.

I've got a challenge for you.

I want to see if you can pull these two interleaved books apart.

-Oh!

-Oh, is it...?!

-It's still not working, is it?

-LAUGHTER

So, why is it so hard to pull the books apart?

Well, it's down to friction.

Friction is caused by two things - at a microscopic level,

the surfaces are uneven and therefore lock into one another.

And also, the molecules of the paper

are very slightly attracted to one another.

When we're talking about two pages, it's very easy to pull them apart.

But when you add up all the friction resulting from

300 pages being on top of each other, it's a different story.

The force of friction is useful to us in all kinds of ways.

The parachute here is creating air resistance, a kind of friction.

It opposes the downward movement of the space capsule,

slowing it down and creating a smoother landing.

It provides the force that keeps the tyres of this car on the road.

Replace tarmac with ice

and the tyres can no longer grip the surface due to reduced friction.

CRUNCH

Next, I'm live and direct,

dissolving things in liquids to demonstrate solubility.

Oh man, I wouldn't mind a nice cup of tea -

I've been talking for ages now!

I've got a question for you guys. Do you think I can fit

this length of polystyrene into this jar?

-Yes.

-No.

No? Yeah? I like that - you lot have got some faith in me!

Excellent.

Right, this is what we're going to do...

We're going to take this length of polystyrene

and stick it into this Pyrex jug.

But we're going to use something to help us do it.

It's this stuff. It's called propanone, or acetone.

We're going to dissolve this polystyrene into this.

And when we dissolve it in, this will be called the solute,

and this stuff, that does the dissolving,

will be called the solvent.

And when they're mixed together, they will be called a solution.

You add a bit of the solvent...

Something's happening.

-GIGGLING

-Slowly but surely,

it's going in.

So, remember, acetone's the stuff that you've actually got

in nail varnish remover.

Aw, yeah!

-Swill that around.

-Hurray!

-One, two, three...! Magic!

-Oh, yes.

So there we have it,

a whole polystyrene rod fitted into a little Pyrex jar.

-Hi. Can I have two cups of tea, please?

-Sure.

'Solubility is a measure of how much solute can dissolve in a solvent.

'The solubility of a solute in a solvent changes with temperature.

'And importantly, it depends on whether the solute

'is a gas or a solid. So, let's look at solids first.'

Here we have two identical hot cups of tea.

And we want to see how much sugar

can be held in solution in these hot cups of tea.

When no more sugar can dissolve, the solution is said to be saturated.

I think that's getting just about saturated now.

But the situation changes when the liquid is cooled down.

Luckily, I've got a bit of dry ice here,

and that should do the job perfectly.

Dry ice is at a temperature of minus 78 degrees centigrade,

so it's going to cool the water down.

In this one a tiny bit of sugar has crystallised at the bottom

because it's a bit cooler. But this one, look how much sugar

is actually in the bottom.

The sugar behaves like most solids - the solubility increases

as the temperature of the solvent does.

What's interesting about gases

is that they behave in the opposite way to solids.

The solubility of gases decreases as the temperature increases.

I'm going to show you a neat trick.

Check out these ice cubes.

One set's lovely and clear,

but the other one's pretty cloudy.

It's all down to the solubility of gases in a liquid.

So to make cloudy ice cubes, all we need to do is, take tap water

and put it straight in.

But if we want our ice cubes to be clear,

you have to boil the water first.

And here's why boiling the water makes a difference.

At room temperature, the water contains a certain amount

of dissolved gases from the air.

The water straight from the tap creates cloudy ice cubes

because these gases that were dissolved in the water

form tiny bubbles in the ice.

By heating the water to boiling point,

we have decreased the solubility of the dissolved gases.

They come out of the solution as bubbles

and the remaining water has less gases dissolved, so is less cloudy.

For a solution, the solubility of gases decreases

as we increase the temperature.

And now we uncover the secret world of photosynthesis,

here in its natural habitat.

Photosynthesis is one of the most important reactions on this planet.

Let's have a look at the word... "Photo" means light,

"synthesis" means to make - and that's exactly what it does.

So, plants harness the energy from the sun to make food.

Photosynthesis happens in the leaves of all green plants.

Without photosynthesis there would be no oxygen in our atmosphere

and life as we know it would not exist.

It happens inside the chloroplasts,

which are found in leaf cells and other green parts of the plant.

Chloroplasts contain a substance called chlorophyll,

which gives the plant its green colour.

Chlorophyll absorbs sunlight and uses its energy

to convert carbon dioxide and water into glucose.

Oxygen is also produced.

Time for a demo here.

Here we have the aquatic plant named Cabomba.

It's very fast at growing

and particularly efficient at photosynthesizing.

We're going to have a look at two things.

First, the oxygen produced.

If photosynthesis is happening,

the gas collected in the tube over the last 30 minutes

should be oxygen.

If it is oxygen, it will re-light this glowing splint.

Wicked!

Second thing, light!

The good thing about using underwater plants

is that you can actually see the oxygen being produced.

The amount of bubbles coming out of the stem of the plant

are a good indication of the rate of photosynthesis.

But what happens if we reduce the light intensity?

It's practically stopped.

See, without light photosynthesis can't happen.

So you can imagine if you were to put this in a pitch black room,

there would be no photosynthesis and hence no bubbles being released.

So for photosynthesis to happen,

we need water, carbon dioxide, chlorophyll and light.

We've already seen that photosynthesis produces oxygen,

but the other product is glucose.

This glucose is the fuel plants need for energy and to grow.

So, essentially, plants make their own food

and in turn, animals rely on plants for their food.

Animals get their food from plants by eating plants directly

or by eating other animals that have already eaten plants.

Plants are the most fundamental part of the food chain.

Photosynthesis is essential to life on this planet for two main reasons.

One is it provides us with oxygen,

and the second is it harnesses the sun's light energy to produce food.

Wooo-hooo!

Some scary cultures now. Who knows what bacteria we're carrying around?

Number two - microorganisms.

Bacteria are a type of microorganism,

each made up of just one cell.

Some bacteria are harmful and cause disease...

and some are useful, like the 100 trillion bacterial cells

that inhabit our digestive system.

Bacteria reproduce by cloning themselves

through binary fission, a kind of asexual reproduction.

In the right conditions, they can reproduce very quickly.

Some species can replicate themselves

in as little as 20 minutes.

We can grow bacteria in an incubator on plates of agar jelly.

With time, nutrients and an optimum temperature.

These girls at Copthall to investigate the bacteria

growing on their possessions.

They took some Petri dishes and they swabbed some of their stuff.

And put them in an incubator

set at just under 30 degrees centigrade to help them grow.

Two days have passed since we put

the agar plates inside the incubator.

So lets have a look what's been grown.

With any scientific experiment, you need a control,

-don't you?

-GIRLS: Yeah.

So, here was our control here.

Whooo!

Nothing at all.

Brilliant. So there's proof that if you just shut one by itself,

you'll have no bacteria.

What've we got here?

Headphones. Got a few speckles here and there.

-GIRL: That's been in my ear!

-That's not too bad.

You've got a few different microorganisms in there.

Earring.

GIRLS: Eugh!

You know what, I'm glad I don't wear earrings!

So there's a lovely pattern being drawn with the earrings

and you can see the bacteria have grown

in exactly the same place as your pattern.

So everyday objects harbour all types of bacteria

and these can be grown in Petri dishes with some surprising

and rather revolting results,

as shown with the help of the girls at Copthall School.

So finally, at number one,

it's a really important subject about how oceans are turning acidic.

It's acids and alkalis.

We live on a blue planet. 70% of the Earth's surface

is made up of oceans, and there's a problem.

The oceans are changing.

We know they're changing because their pH is changing.

So what does this really mean?

The pH of a solution is a measure of how acidic or alkaline it is.

We can use a universal indicator

to work out the pH levels of different solutions.

If the solution goes green, then it's neutral.

If the solution goes red, then it's very acidic.

And if the solution goes purple, then it is very alkaline.

In fact, if you go through the pH scale

you can get all the colours of the rainbow!

Different parts of the body need different pH levels

to operate efficiently.

The blood has a pH that is very slightly alkaline,

while the stomach needs an acidic pH.

It's the same for aquatic life.

Oceans provide a pH between 7.8 and 8.4

that aquatic life thrives in, but scientists are worried

that the pH of our oceans is now becoming more acidic.

Most scientists believe that this acidification is due

to the CO2 that we are producing, being absorbed by the oceans.

Professor Sella has prepared a simple demo to show

what is happening to our oceans.

The water in this jar has some universal indicator in it

and we can use that to represent the ocean.

We're going to put in a bit of alkali.

First of all, Andrea adds some alkali

so the solution now matches the pH of the ocean, around 8.1.

Nice and purple. OK?

And now we're going to add the carbon dioxide.

Carbon dioxide is actually dry ice.

It's going to bubble and bubble. Watch what happens to the pH.

Boiling away, great effect.

This is happening in our lifetime,

and you can see it's already gone from purple...

To me, its beginning to look blue-ish green.

So we're gradually coming towards neutral,

and if you wait a moment longer,

it's gradually going paler and paler.

We're really past the neutral point.

We're actually into the acidic region.

So as the carbon dioxide bubbles through the water,

it's turning the water more acidic?

Absolutely. What it's doing is making something called carbonic acid,

and this is happening with our atmosphere

much more slowly,

as the CO2 dissolves in the oceans, becoming more acidic.

There are really big questions about what happens

to living things in the oceans.

The oceans certainly should be just slightly alkaline,

just away from neutral, and what's happening is that they're slowly

moving down towards more acidic conditions.

That's why the world needs scientists in the future,

to help tackle some of these big changes to our planet.

So there we have it, my Top 20 Demonstrations. Hope you enjoyed it!

They're all online at...

..including some extra ones!

And, of course, the full-length version of my photosynthesis rap!

Subtitles by Red Bee Media Ltd