0:00:02 > 0:00:04I'm Jon Chase, and I'm a scientist.
0:00:04 > 0:00:06Science is everywhere.
0:00:06 > 0:00:07Science is amazing!
0:00:12 > 0:00:13In the next 60 minutes,
0:00:13 > 0:00:16I'm going to show you my top 20 science demos.
0:00:16 > 0:00:18Oh, that's warm!
0:00:19 > 0:00:22Kicking off at number 20 is osmosis.
0:00:22 > 0:00:25Big shout to the students at Copthall School
0:00:25 > 0:00:27for throwing stuff at me.
0:00:27 > 0:00:29All life needs water.
0:00:29 > 0:00:33Water moves in and out of living cells across their cell membranes.
0:00:33 > 0:00:35These membranes are partially
0:00:35 > 0:00:36or selectively permeable.
0:00:36 > 0:00:39Check which term you need to use.
0:00:41 > 0:00:43Osmosis is a special type of diffusion
0:00:43 > 0:00:46which happens across a membrane, always in regards to water.
0:00:46 > 0:00:49The hockey net represents the membrane.
0:00:49 > 0:00:51You have some water molecules.
0:00:51 > 0:00:54The blue balls represent water molecules
0:00:54 > 0:00:57and the other colours are different-sized solute molecules
0:00:57 > 0:00:59which are dissolved in the water.
0:00:59 > 0:01:03I want you to send different-sized molecules
0:01:03 > 0:01:05at this membrane
0:01:05 > 0:01:07and see what happens.
0:01:07 > 0:01:11The net only lets the smaller blue balls through
0:01:11 > 0:01:14and this is what happens in osmosis.
0:01:15 > 0:01:19When water molecules move from a high water concentration
0:01:19 > 0:01:21to a low water concentration across a membrane,
0:01:21 > 0:01:24the process is called osmosis.
0:01:24 > 0:01:26Water molecules actually move
0:01:26 > 0:01:29back and forth across the membrane all the time.
0:01:29 > 0:01:31But overall, there is a movement of water
0:01:31 > 0:01:33from an area of higher water concentration
0:01:33 > 0:01:36to an area of lower water concentration.
0:01:36 > 0:01:39The overall movement is called the net flow. Get it?
0:01:39 > 0:01:41I feel a rap coming on.
0:02:22 > 0:02:26Plants use osmosis to take in water through their roots.
0:02:26 > 0:02:30The net flow of water into the plant causes the plant cells to expand
0:02:30 > 0:02:32so they become turgid or stiff.
0:02:33 > 0:02:36This means they are able to hold the plant upright.
0:02:36 > 0:02:41However, for animal cells, osmosis can cause problems
0:02:41 > 0:02:44as animal cells have no cell wall, and there is a danger
0:02:44 > 0:02:47they may take in so much water that they explode.
0:02:47 > 0:02:48This is called lysis.
0:02:48 > 0:02:50There is also a danger
0:02:50 > 0:02:52that so much water moves out
0:02:52 > 0:02:55that they become irreparably damaged, like this blood cell.
0:02:55 > 0:02:58When this happens, this is known as crenation.
0:02:58 > 0:03:00Our bodies stop this from happening
0:03:00 > 0:03:03by carefully regulating the concentration of our tissue fluid.
0:03:03 > 0:03:07It's complicated stuff, so how about another rap to help clear things up?
0:03:50 > 0:03:53So, bottom line - Osmosis is the net movement of water
0:03:53 > 0:03:56from an area of high water concentration
0:03:56 > 0:03:58to one of lower water concentration
0:03:58 > 0:04:01across a selectively or partially permeable membrane.
0:04:04 > 0:04:06And now, the race is on.
0:04:06 > 0:04:09Racing chemicals - rates of reactions at number 19.
0:04:11 > 0:04:15Chemical reactions are all about collisions between particles
0:04:15 > 0:04:18and the rate of reaction depends on how frequently particles collide
0:04:18 > 0:04:20and with how much energy.
0:04:20 > 0:04:23There are four methods of increasing the rate of reaction.
0:04:23 > 0:04:27My mate Professor Sella is going to talk me through them.
0:04:27 > 0:04:29First up - concentration.
0:04:29 > 0:04:31What we're going to do is set up these three reactions.
0:04:31 > 0:04:34This one's going to be the high concentration one.
0:04:34 > 0:04:37You can see there's more stuff in it.
0:04:37 > 0:04:40We're going to put a medium one, and then finally
0:04:40 > 0:04:43we'll have a low concentration one down at the other side.
0:04:43 > 0:04:45This is going to be like a race.
0:04:45 > 0:04:47We're going to start them off
0:04:47 > 0:04:49and when we get to the end of the race,
0:04:49 > 0:04:51the solution is going to turn blue.
0:04:51 > 0:04:53- Are you ready?- Yeah.- Steady, go!
0:04:53 > 0:04:56And now, let's just mix them up.
0:04:56 > 0:05:00'The reaction in the beaker finishes with the sudden release of iodine
0:05:00 > 0:05:04'which interacts with the starch that is already present
0:05:04 > 0:05:07'to turn the solution blue almost instantly.'
0:05:07 > 0:05:09We have the reaction going
0:05:09 > 0:05:12and we're waiting for those racers to get to the end.
0:05:12 > 0:05:15Firm favourite is High Concentration.
0:05:15 > 0:05:17Also in the running is Medium Concentration.
0:05:18 > 0:05:21Bringing up the rear is Low Concentration.
0:05:21 > 0:05:23Whoa! There went the first!
0:05:23 > 0:05:25As expected, the firm favourite,
0:05:25 > 0:05:28High Concentration, comes storming through the finish line.
0:05:28 > 0:05:31Now, what about this one?
0:05:31 > 0:05:33I'm wondering if that one's going to go.
0:05:33 > 0:05:35- What?- There went the second one.
0:05:36 > 0:05:40The runners are coming in exactly in the order that we were expecting.
0:05:40 > 0:05:43And that one, he's been out of training or something.
0:05:43 > 0:05:44I wouldn't bet on that guy.
0:05:44 > 0:05:46That's not... Ooh! There it went.
0:05:46 > 0:05:48Of the three solutions added,
0:05:48 > 0:05:50it was the solution with the highest concentration
0:05:50 > 0:05:53that resulted in the quickest reaction.
0:05:53 > 0:05:55Because the reactant particles are more crowded,
0:05:55 > 0:05:57collisions take place more frequently.
0:05:57 > 0:05:59So that was concentration.
0:05:59 > 0:06:01Now onto temperature.
0:06:01 > 0:06:02When the temperature is increased,
0:06:02 > 0:06:05the particles in the solution move more quickly.
0:06:05 > 0:06:07This increases the frequency of collisions
0:06:07 > 0:06:09and the energy with which they hit each other.
0:06:09 > 0:06:13We're going to see how temperature affects the rate of reaction.
0:06:13 > 0:06:16We'll do that by using a glow stick which reacts when we break it.
0:06:21 > 0:06:24Now let's see what would happen if we cooled it down.
0:06:26 > 0:06:29So as you can see, the reaction gives off light
0:06:29 > 0:06:31but this isn't giving off light
0:06:31 > 0:06:34so the reaction appears to have slowed down.
0:06:34 > 0:06:36If we cool it down and the reaction slows down,
0:06:36 > 0:06:39what happens if we heat it up? Let's give it a go.
0:06:39 > 0:06:41A bit of friction to heat it up.
0:06:45 > 0:06:49And as we warm up the solution, what happens to the reaction?
0:06:49 > 0:06:53Well, it's started to give off light again. Even more light than that,
0:06:53 > 0:06:55and because it's now got warmer,
0:06:55 > 0:06:57the reaction has sped up.
0:06:57 > 0:07:00So we can say that increase in temperature speeds up a reaction
0:07:00 > 0:07:04and decrease in a temperature slows down a reaction.
0:07:04 > 0:07:08So stick it in your freezer if you want to keep it for tomorrow
0:07:08 > 0:07:10to have more raving. Right, I'm off.
0:07:11 > 0:07:13Next up are catalysts.
0:07:13 > 0:07:17They work by speeding up a reaction and they do this by increasing
0:07:17 > 0:07:21the number of successful collisions between particles.
0:07:21 > 0:07:24Back to Professor Sella and his great experiments.
0:07:24 > 0:07:26Here we have hydrogen peroxide
0:07:26 > 0:07:29and I'm going to add a little bit of a solid catalyst.
0:07:29 > 0:07:31This is manganese dioxide, tiny bit.
0:07:31 > 0:07:35Can you see the tiny little flecks
0:07:35 > 0:07:38of manganese dioxide are actually causing the reaction?
0:07:38 > 0:07:40They're causing hydrogen peroxide
0:07:40 > 0:07:42to decompose to oxygen and water.
0:07:42 > 0:07:46So they're reacting and remaining unchanged now?
0:07:46 > 0:07:51Absolutely. It's interesting that on this side we have the same hydrogen peroxide, but without the catalyst
0:07:51 > 0:07:54and actually, it decomposes very, very slowly.
0:07:54 > 0:07:57Even if you leave it in the fridge, eventually it will go off.
0:07:57 > 0:08:01Let's not mess around, let's give it a real load of catalyst.
0:08:01 > 0:08:03Do I have to step back for this?
0:08:03 > 0:08:05Well, you'll see. Go!
0:08:06 > 0:08:08It's actually gotten so hot
0:08:08 > 0:08:11that it's boiling. You can see a plume of water vapour
0:08:11 > 0:08:13accompanies the oxygen as it comes out.
0:08:13 > 0:08:16The catalyst is causing the breakdown of hydrogen peroxide
0:08:16 > 0:08:18into water and oxygen at a phenomenal rate.
0:08:18 > 0:08:22But the catalyst has not changed at all throughout this reaction.
0:08:22 > 0:08:23The catalyst is still there.
0:08:23 > 0:08:26We could pour this all off, we could filter it away
0:08:26 > 0:08:30and we would collect all of that black stuff. That's our catalyst.
0:08:30 > 0:08:33And finally, the size of particles.
0:08:33 > 0:08:36How does that affect the rate of reaction?
0:08:36 > 0:08:37Let's burn this sugar lump.
0:08:44 > 0:08:46Well, it burns a bit.
0:08:48 > 0:08:52As it burns, the sugar is turned into carbon dioxide and water.
0:08:54 > 0:08:57What about if we decrease the particle size?
0:08:57 > 0:09:01Using something like icing sugar. Using a smaller particle size
0:09:01 > 0:09:02increases the surface area.
0:09:02 > 0:09:06We've used the same amount of sugar as is in this cube
0:09:06 > 0:09:09and we've put it into this tube.
0:09:10 > 0:09:13Let's see what happens when we try and burn it this time.
0:09:17 > 0:09:20There was a lot more reacting going on, and a lot more heat.
0:09:20 > 0:09:22I could even feel it coming off.
0:09:22 > 0:09:24'So by breaking down the sugar into a powder,
0:09:24 > 0:09:26'its surface area increased.
0:09:26 > 0:09:30'More of the sugar has been exposed to the oxygen in the atmosphere
0:09:30 > 0:09:33'so collisions can take place more frequently.'
0:09:33 > 0:09:36Decreasing the size of the particle increases the rate of reaction
0:09:36 > 0:09:40and that's because we have increased the surface area.
0:09:40 > 0:09:41So, let's recap.
0:09:41 > 0:09:44To increase the rate of a reaction,
0:09:44 > 0:09:46the concentration needs to increase
0:09:46 > 0:09:48or the temperature needs to increase
0:09:48 > 0:09:51or the size of particles needs to decrease.
0:09:51 > 0:09:54And the other way to increase the rate of reaction
0:09:54 > 0:09:55is to use a catalyst.
0:09:55 > 0:09:57At number 18 is mitosis,
0:09:57 > 0:10:01explained through the medium of dance - and rap.
0:10:01 > 0:10:04Wouldn't it be great if we could clone ourselves?
0:10:04 > 0:10:07Well, the cells in our bodies do this all the time
0:10:07 > 0:10:10by a process called mitosis.
0:10:10 > 0:10:14It is one of the most basic and beautiful processes on the planet.
0:10:14 > 0:10:16'It's just like a dance.
0:10:16 > 0:10:19'So I've got the pupils here at Copthall School
0:10:19 > 0:10:21'to show you how it works.
0:10:21 > 0:10:24'So get settled and check out my mitosis rap!'
0:10:41 > 0:10:44Mitosis is a type of cell replication
0:10:44 > 0:10:46that enables cells to clone themselves.
0:10:46 > 0:10:49It's essential to growth and repair.
0:10:49 > 0:10:53It's a brilliant, simple cycle that is fundamental to life.
0:10:53 > 0:10:55When you see mitosis through a microscope,
0:10:55 > 0:10:58it looks like a dance of the chromosomes.
0:10:58 > 0:11:01We're looking at a cell with only a few chromosome dancers.
0:11:06 > 0:11:09A human cell contains 23 pairs of chromosomes.
0:11:09 > 0:11:13The mitosis cycle starts with the chromosomes of the parent cell
0:11:13 > 0:11:17making identical copies of themselves, so when the cell divides
0:11:17 > 0:11:20there will be identical chromosomes in each dividing half.
0:11:20 > 0:11:23Then the doubled chromosomes line up
0:11:23 > 0:11:25along the central axis of the cell
0:11:25 > 0:11:28and microtubules called spindle fibres pull them apart
0:11:28 > 0:11:30to opposite ends of the cell.
0:11:32 > 0:11:35Now, each end of the cell has a full set of chromosomes
0:11:35 > 0:11:38around which a nucleus forms.
0:11:38 > 0:11:41Then the cell membrane pinches in between the two nuclei,
0:11:41 > 0:11:45dividing the original cell into two new daughter cells.
0:11:45 > 0:11:49The daughter cells are genetically identical to the parent cell.
0:11:49 > 0:11:51The parent cell has cloned itself
0:11:51 > 0:11:53and the cycle begins again.
0:11:55 > 0:11:57Can I have a parent cell, please?
0:12:40 > 0:12:43And now some alchemy, as I turn copper into gold.
0:12:43 > 0:12:45Well, not exactly, but it's still impressive.
0:12:45 > 0:12:49It's electrolysis: electroplating at number 17.
0:12:49 > 0:12:52Electrolysis - so what does it mean?
0:12:52 > 0:12:54Well, let's split up the word.
0:12:54 > 0:12:56Electro - electricity.
0:12:56 > 0:12:58Lysis - splitting.
0:12:58 > 0:13:02So electrolysis is splitting a substance by means of electricity.
0:13:02 > 0:13:06And it's very useful. Electrolysis can be used to plate jewellery.
0:13:06 > 0:13:09Ever wondered how gold can be so cheap?
0:13:09 > 0:13:12Well, electrolysis can be used for electroplating,
0:13:12 > 0:13:17where one metal is coated with another, so it's not solid gold.
0:13:17 > 0:13:19But bling ain't my thing, so in this demo
0:13:19 > 0:13:21I'll plate a copper coin with zinc from a nail.
0:13:22 > 0:13:26'First of all, we need an electrolyte.
0:13:26 > 0:13:28'This is a liquid that conducts electricity.
0:13:28 > 0:13:32'In this case, we're going to use dilute hydrochloric acid.'
0:13:32 > 0:13:35Next, we need a source of electricity.
0:13:42 > 0:13:45'I've attached the negative end of the battery to the coin
0:13:45 > 0:13:47'and the positive end to the nail.
0:13:47 > 0:13:50'Let's see what happens.'
0:14:04 > 0:14:07And there it is, a zinc-plated penny.
0:14:11 > 0:14:13So how does it work?
0:14:13 > 0:14:16The battery causes electrons to be removed from the positive electrode,
0:14:16 > 0:14:19which is called the anode.
0:14:19 > 0:14:21Electrons are forced by the battery
0:14:21 > 0:14:22onto the copper coin,
0:14:22 > 0:14:23which is the cathode.
0:14:25 > 0:14:29At the anode, two electrons are removed from each zinc atom,
0:14:29 > 0:14:33turning them into positively-charged zinc ions.
0:14:33 > 0:14:37These zinc ions are attracted to the negatively-charged cathode,
0:14:37 > 0:14:38where they gain electrons.
0:14:38 > 0:14:41This turns the zinc ions back into zinc atoms,
0:14:41 > 0:14:43which explains why the copper coin
0:14:43 > 0:14:46is coated with a layer of zinc.
0:14:46 > 0:14:48And that's how the coin becomes zinc-plated.
0:14:48 > 0:14:52Right. I'm off to go spend a penny.
0:14:54 > 0:14:56Time to look beneath the surface,
0:14:56 > 0:14:59with microscopy at number 16.
0:14:59 > 0:15:02We can see objects as small as 0.1 millimetres
0:15:02 > 0:15:06and that means we can just about see these lice eggs in our hair
0:15:06 > 0:15:10and tiny single-celled organisms like amoeba,
0:15:10 > 0:15:12but it's possible to see things much smaller than that
0:15:12 > 0:15:15if we use magnification.
0:15:15 > 0:15:18There's three types of microscope - light, like this one here
0:15:18 > 0:15:21and two types of electron microscope
0:15:21 > 0:15:22like those ones over there.
0:15:25 > 0:15:27'Light microscopes use light and mirrors
0:15:27 > 0:15:30'and can see things as small as 400 nanometres.'
0:15:30 > 0:15:33This allows us to get down to the world of the cell
0:15:33 > 0:15:37and that means some pretty amazing things can be seen.
0:15:38 > 0:15:41Here's an amoeba engulfing red blood cells
0:15:41 > 0:15:44and red and white blood cells moving through a tiny blood vessel.
0:15:44 > 0:15:47And human sperm.
0:15:47 > 0:15:51A leaf surface at 600 times magnification
0:15:51 > 0:15:55and the head of a dog tapeworm no bigger than a grain of rice.
0:15:55 > 0:15:57Plant cells crammed with chloroplasts.
0:15:57 > 0:16:00Look at these glucose crystals.
0:16:00 > 0:16:02But light microscopes have a limit.
0:16:02 > 0:16:05Any object that's smaller than the wavelength of light
0:16:05 > 0:16:09appears blurred. But in the 1930s,
0:16:09 > 0:16:11a new kind of microscope was invented,
0:16:11 > 0:16:14which took our eyes further than they'd ever been before,
0:16:14 > 0:16:17to places we'd never seen before - the electron microscope.
0:16:17 > 0:16:19The specimen is put in a vacuum
0:16:19 > 0:16:21and is viewed not by light waves
0:16:21 > 0:16:25but by a single beam of electrons
0:16:25 > 0:16:28that scans the surface, building up an image on a screen
0:16:28 > 0:16:29rather like a television picture.
0:16:32 > 0:16:36Because electrons have a wavelength 100,000 times smaller than light,
0:16:36 > 0:16:40electron microscopes can magnify objects up to 10 million times.
0:16:41 > 0:16:45There are two types of electron microscope - the transmission
0:16:45 > 0:16:47and the scanning.
0:16:47 > 0:16:51The scanning electron microscope scatters electrons
0:16:51 > 0:16:56across the surface of a specimen. It can magnify in incredible detail.
0:16:56 > 0:16:59This is a leaf surface under a scanning electron microscope.
0:16:59 > 0:17:03Both types of electron microscopes make black-and-white images
0:17:03 > 0:17:05but these have been colourised to make them clearer
0:17:05 > 0:17:07and a lot more appealing to the eye.
0:17:07 > 0:17:08Check out this fruit fly.
0:17:10 > 0:17:12A pubic louse and its claws.
0:17:12 > 0:17:14Cancer cells splitting.
0:17:16 > 0:17:17A blood clot.
0:17:17 > 0:17:21And human sperm cells on the surface of an egg.
0:17:21 > 0:17:24But what about a transmission electron microscope?
0:17:26 > 0:17:29The difference with a transmission electron microscope
0:17:29 > 0:17:31is that it sees THROUGH things.
0:17:31 > 0:17:33It does this by sending beams of electrons
0:17:33 > 0:17:37rather than light, through ultra-thin specimens.
0:17:37 > 0:17:41Using these microscopes, we're able to study the interior of cells
0:17:41 > 0:17:43and their organelles
0:17:43 > 0:17:46and we've been able to get a better understanding of how pathogens,
0:17:46 > 0:17:49such as viruses, invade cells,
0:17:49 > 0:17:52like these HIV particles budding on the surface of a T cell.
0:17:55 > 0:17:57Now a new type of electron microscope,
0:17:57 > 0:17:59a tunnelling electron microscope,
0:17:59 > 0:18:03has even made it possible to see the arrangement of atoms.
0:18:03 > 0:18:05Just how far will microscopy go?
0:18:08 > 0:18:12Now, throwing yourself out of a plane may not be your idea of fun
0:18:12 > 0:18:14but if it's all in the name of science...
0:18:14 > 0:18:17At number 15, falling bodies.
0:18:17 > 0:18:18Aaagh!
0:18:21 > 0:18:23Science is always evolving.
0:18:23 > 0:18:26About 2,000 years ago, this guy here, Aristotle,
0:18:26 > 0:18:30said the rate of acceleration with which a body falls to the ground
0:18:30 > 0:18:31depends on its mass.
0:18:31 > 0:18:33Look at these bodies falling.
0:18:33 > 0:18:36Why have some accelerated to a greater speed then others?
0:18:36 > 0:18:39If Aristotle was right and acceleration depends on mass,
0:18:39 > 0:18:41this would mean a heavier body
0:18:41 > 0:18:44would drop at a different acceleration to a lighter body.
0:18:44 > 0:18:47So, let's give it a try.
0:18:47 > 0:18:49At ground level, we have Jessica with a camera
0:18:49 > 0:18:52to record the exact point when the ball hits the ground.
0:18:52 > 0:18:56Hello, girls. Right, to the left, we have a cricket ball
0:18:56 > 0:19:01and that's three times greater mass than the tennis ball,
0:19:01 > 0:19:04so let's drop them at the same time and see what happens.
0:19:04 > 0:19:07OK, are you ready? Three,
0:19:07 > 0:19:09two, one,
0:19:09 > 0:19:10drop!
0:19:13 > 0:19:15How did it look, Jessica?
0:19:15 > 0:19:18- They looked like they dropped at the same time.- Wicked.
0:19:18 > 0:19:22Looking at Jessica's footage, it looks like the balls do indeed
0:19:22 > 0:19:23hit the ground at the same time,
0:19:23 > 0:19:25even though the cricket ball
0:19:25 > 0:19:28is three times heavier than the tennis ball.
0:19:28 > 0:19:32So our experiment shows that Aristotle was wrong.
0:19:32 > 0:19:35The balls drop at the same rate, regardless of their mass.
0:19:35 > 0:19:39The first person to point this out was Galileo,
0:19:39 > 0:19:42who according to legend, did the same experiment
0:19:42 > 0:19:44from the Tower of Pisa 500 years ago.
0:19:44 > 0:19:46So if the balls landed at the same time,
0:19:46 > 0:19:49the same should be true of a hammer and a feather, right?
0:19:49 > 0:19:52Well, let's give it a shot.
0:19:52 > 0:19:53Three, two, one.
0:19:56 > 0:19:57What happened there?
0:19:57 > 0:20:02Air resistance affects the feather - that's why it falls less quickly.
0:20:02 > 0:20:04That's right, it is air resistance!
0:20:04 > 0:20:08Air resistance is stopping the feather from falling
0:20:08 > 0:20:11to the ground at the same rate as the hammer.
0:20:11 > 0:20:13Remember our skydivers?
0:20:13 > 0:20:15They're able to change their rate of acceleration
0:20:15 > 0:20:18by making themselves more or less streamlined.
0:20:18 > 0:20:21If we remove the effect of air resistance, all falling bodies
0:20:21 > 0:20:25should fall at the same rate, regardless of their mass.
0:20:25 > 0:20:26So let's go to a place where
0:20:26 > 0:20:28we can try this experiment with no air resistance -
0:20:28 > 0:20:31does anyone know a good place where we could do that?
0:20:31 > 0:20:34- In space!- Yes! A vacuum in space!
0:20:34 > 0:20:36During the fourth moon landing,
0:20:36 > 0:20:39Galileo's theory was put to the test.
0:20:39 > 0:20:42'Here in my left hand I have a feather -
0:20:42 > 0:20:45'in my right hand, a hammer.
0:20:45 > 0:20:47'And I guess one of the reasons we got here today
0:20:47 > 0:20:50'was because of a gentleman named Galileo
0:20:50 > 0:20:54'a long time ago, who made a rather significant discovery
0:20:54 > 0:20:57'about falling objects and gravity fields.
0:20:57 > 0:21:00'And we thought, where would be a better place
0:21:00 > 0:21:04'to confirm his findings than on the moon?
0:21:04 > 0:21:07'I'll drop the two of them here, and hopefully they'll
0:21:07 > 0:21:09'hit the ground at the same time...
0:21:11 > 0:21:13'How about that?
0:21:13 > 0:21:17'That means that Mr Galileo was correct - and his findings...'
0:21:17 > 0:21:20The feather and the hammer land at the same time.
0:21:20 > 0:21:23Unlike Earth, the moon has no atmosphere
0:21:23 > 0:21:26so there's no air resistance to interfere with the experiment.
0:21:26 > 0:21:30The moon's gravity causes them to fall with the same acceleration -
0:21:30 > 0:21:33even though they have very different masses.
0:21:33 > 0:21:36It's a shame Galileo wasn't around to see that.
0:21:36 > 0:21:41And for my next trick, I will make money disappear!
0:21:41 > 0:21:43Easier than it looks!
0:21:45 > 0:21:48For this experiment, I'm going to show you
0:21:48 > 0:21:53a disappearing act, with the help of just a coin and a glass of water.
0:21:53 > 0:21:56Here we have one coin - simply take a glass,
0:21:56 > 0:21:58stick it over the top!
0:21:58 > 0:22:01To make the coin disappear, we add a bit of water.
0:22:05 > 0:22:07And hey, presto!
0:22:08 > 0:22:11The question is, why does the coin disappear?
0:22:11 > 0:22:14From the top, you can see the coin is still there,
0:22:14 > 0:22:18but from the side, the coin isn't visible.
0:22:18 > 0:22:22When there's no water in the glass, light from the coin travels
0:22:22 > 0:22:26through the glass to our eyes at a particular angle.
0:22:26 > 0:22:29When water's added, the light from the coin hits
0:22:29 > 0:22:33the inside of the glass at an angle that's greater
0:22:33 > 0:22:36than what is known as the critical angle.
0:22:36 > 0:22:39Once this happens, all the light from the coin
0:22:39 > 0:22:41is totally internally reflected,
0:22:41 > 0:22:45and it can only escape through the top of the glass.
0:22:46 > 0:22:51Here's another cool trick that uses total internal reflection.
0:22:51 > 0:22:55I've created a stream of water by making a hole in this bottle.
0:22:55 > 0:22:57If I shine the laser in the right place,
0:22:57 > 0:23:01the laser hits the opening of the hole
0:23:01 > 0:23:05and it travels down the actual beam of water.
0:23:05 > 0:23:09The light is being totally internally reflected,
0:23:09 > 0:23:11and trapped within the water.
0:23:11 > 0:23:14Lasers in experiments should always be clamped
0:23:14 > 0:23:15or stable on a bench,
0:23:15 > 0:23:19as they can be dangerous if they shine into anyone's eyes.
0:23:22 > 0:23:26In this fibre-optic lamp, light enters one end of the fibre
0:23:26 > 0:23:30just like the light from the laser entering the stream of water,
0:23:30 > 0:23:35and this is reflected repeatedly until it emerges at the other end.
0:23:37 > 0:23:40Optical fibres have revolutionised the way we communicate,
0:23:40 > 0:23:44carrying data as pulses of light over incredible distances
0:23:44 > 0:23:48and creating the information superhighway.
0:23:48 > 0:23:52It's time to heat things up a little on a cold day in Scotland...
0:23:52 > 0:23:56Number 13 - endothermic and exothermic reactions.
0:23:57 > 0:23:59We all know that some chemical reactions
0:23:59 > 0:24:01release energy in the form of heat.
0:24:01 > 0:24:04But what about reactions that do the opposite?
0:24:04 > 0:24:08I'm at this shopping centre in Edinburgh on a chilly Saturday
0:24:08 > 0:24:11to demonstrate endothermic and exothermic processes.
0:24:13 > 0:24:15- Are your hands cold?- Yeah.- Aye.
0:24:15 > 0:24:17- And you've heard of these, haven't you, hand-warmers?- No!
0:24:17 > 0:24:21You haven't heard of a hand-warmer? You haven't seen these?
0:24:21 > 0:24:23When your hands are cold, crack this inside
0:24:23 > 0:24:25and this makes your hands warm.
0:24:25 > 0:24:29- You've all seen water turn into ice, yeah?- Yeah.
0:24:29 > 0:24:32This is going to turn into something that will seem like ice,
0:24:32 > 0:24:35it will go crystalline, but it will get hot. I'm going to cut it open...
0:24:35 > 0:24:37- Bang! - LAUGHTER
0:24:37 > 0:24:42Right, here we go. I'm going to pour it into here...
0:24:42 > 0:24:46- You know that that was pretty cold when you touched it, yeah?- Yeah.
0:24:46 > 0:24:50- Right... You want to touch it underneath? Cold?- Yeah, that's cold.
0:24:50 > 0:24:53We need something to kick it off,
0:24:53 > 0:24:56for it to give off heat to warm your hands.
0:24:56 > 0:24:59- So we're going to stick something in it.- Fire!- Right...
0:25:01 > 0:25:04- Oh, what are you doing?- Oh...!
0:25:04 > 0:25:06Oh, that's warm!
0:25:06 > 0:25:10It's getting warm, is it?! But I thought you said it was cold?!
0:25:10 > 0:25:13'What is happening here? The blue liquid is actually a super-saturated
0:25:13 > 0:25:16'solution of sodium ethanoate.
0:25:16 > 0:25:18'The liquid is so full of sodium ethanoate
0:25:18 > 0:25:21'that it's very close to becoming a solid.
0:25:21 > 0:25:23'I just have to put in this wooden stick
0:25:23 > 0:25:27'to start off the process, and the liquid turns into a crystal.
0:25:27 > 0:25:32'Because it releases energy, we call it an exothermic process.
0:25:32 > 0:25:36'It's easy to remember, because energy "exits".
0:25:36 > 0:25:41'Some chemical processes actually absorb energy. Check this out...'
0:25:41 > 0:25:46What I'm going to do is, I'm going to try to get this to stick to that.
0:25:46 > 0:25:48- Stick to the plank of wood? - You need glue.
0:25:48 > 0:25:50Glue? You could use glue.
0:25:50 > 0:25:52Has anyone ever been in a really cold place
0:25:52 > 0:25:54and it says, "Don't lick the pole?"
0:25:54 > 0:25:57Don't do it. You go skiing, and you get stuck to it, and that's
0:25:57 > 0:26:01your holiday finished because your tongue's stuck to this pole.
0:26:01 > 0:26:03We're going to do the same thing with that.
0:26:06 > 0:26:08So I'll grab some of this.
0:26:11 > 0:26:14All right, now, put that lid back on.
0:26:16 > 0:26:18So, you put in some of that.
0:26:18 > 0:26:23Now, mix it together. See that smell? Really smelly...?
0:26:23 > 0:26:27- That's what ammonia is. - That's Thomas's feet!
0:26:27 > 0:26:29- Oh!- I can't smell it myself.
0:26:29 > 0:26:33'The ammonium is a by-product of the reaction taking place in the beaker.
0:26:33 > 0:26:36'For this reaction to take place at room temperature,
0:26:36 > 0:26:40'energy must be absorbed from the surroundings in the form of heat.
0:26:40 > 0:26:41'So much heat is being absorbed
0:26:41 > 0:26:44'that it's freezing the water underneath the beaker.
0:26:44 > 0:26:47'This is an endothermic reaction.'
0:26:47 > 0:26:50Heat is taken from the surroundings and goes into it, so it's
0:26:50 > 0:26:53"indo-thermic" or endothermic - that's how I remember it.
0:26:53 > 0:26:58Endo's like indo and exo is like, well, exit!
0:26:58 > 0:27:01OK, could someone hold this beaker please?
0:27:01 > 0:27:03Huh?!
0:27:03 > 0:27:07This has taken all of the heat out of the water and cooled it down.
0:27:07 > 0:27:10It's cold, isn't it? Right, so, let me break that off...
0:27:10 > 0:27:13You can't get it off!
0:27:13 > 0:27:15When you take heat from water, it gets cold
0:27:15 > 0:27:17and it turns into ice -
0:27:17 > 0:27:20and that...was an endothermic reaction.
0:27:20 > 0:27:24How do you know that's not long-lasting glue?
0:27:27 > 0:27:29It's water.
0:27:29 > 0:27:34More magic now - making the handle of a Pyrex kitchen jug disappear.
0:27:34 > 0:27:37You never know - might come in handy some day...maybe!
0:27:37 > 0:27:39The power of invisibility -
0:27:39 > 0:27:42it's not just the stuff of science fiction and superheroes.
0:27:42 > 0:27:46It's a reality! This is the handle of a Pyrex jug.
0:27:46 > 0:27:49It's perfectly visible, right?
0:27:49 > 0:27:52But watch what happens when I add some vegetable oil...
0:27:52 > 0:27:54Woah! The handle's disappeared!
0:27:56 > 0:28:00The reason this happens is because light refracts.
0:28:00 > 0:28:04Light moves at different speeds through different substances,
0:28:04 > 0:28:08and this speed is measured by something called refractive index.
0:28:08 > 0:28:10When light travels through two substances
0:28:10 > 0:28:12with different refractive indexes,
0:28:12 > 0:28:16it changes direction at the boundary between the two substances,
0:28:16 > 0:28:18if it's travelling at an angle.
0:28:18 > 0:28:22This can be seen here by shining a light through a glass block.
0:28:22 > 0:28:24This change in direction is called refraction.
0:28:24 > 0:28:29Refraction makes looking at objects under water quite tricky,
0:28:29 > 0:28:32since water and air have different refractive indexes.
0:28:32 > 0:28:35The light from objects under water
0:28:35 > 0:28:37changes direction when it leaves the water,
0:28:37 > 0:28:41making them appear in a different place to where they actually are.
0:28:41 > 0:28:45Diving birds have to make this adjustment when looking for fish.
0:28:45 > 0:28:48An object is only visible if it reflects or refracts light.
0:28:48 > 0:28:52When the glass is empty, the handle of the jug is visible because
0:28:52 > 0:28:55the air in the glass has a different refractive index to the Pyrex.
0:28:55 > 0:28:59But the vegetable oil has a similar refractive index to the Pyrex.
0:28:59 > 0:29:04When we add oil to the glass, the light leaving the handle
0:29:04 > 0:29:08no longer refracts, and hey, presto, the handle disappears!
0:29:09 > 0:29:13Ever wondered what your liver was for? Worth looking after it!
0:29:13 > 0:29:15Enzymes!
0:29:16 > 0:29:20There are tens of thousands of chemical reactions
0:29:20 > 0:29:23going on inside our bodies all the time. I'm at a farmers' market
0:29:23 > 0:29:28in Edinburgh to show people how enzymes contained in an animal liver
0:29:28 > 0:29:31can help turn a dangerous chemical like hydrogen peroxide
0:29:31 > 0:29:33into something totally safe.
0:29:33 > 0:29:35Welcome to the wonderful world of enzymes!
0:29:35 > 0:29:38Do you know what your liver's good for?
0:29:38 > 0:29:41- Not really. - What your liver's good for...
0:29:41 > 0:29:43is for breaking down stuff.
0:29:43 > 0:29:46- I'm going to show you how that works.- OK.
0:29:46 > 0:29:48First, I'm going to take some of this stuff.
0:29:48 > 0:29:51Put on my safety goggles...
0:29:51 > 0:29:54Hydrogen peroxide - you can use it
0:29:54 > 0:29:57to bleach your hair if you like, to look pretty!
0:29:57 > 0:29:58When you eat stuff,
0:29:58 > 0:30:03your body breaks it down, but it can produce some harmful chemicals,
0:30:03 > 0:30:04and this is one of them.
0:30:04 > 0:30:08Because it's the detox organ in the body, the liver is full of enzymes
0:30:08 > 0:30:13that work as catalysts to speed up the breakdown of harmful chemicals.
0:30:13 > 0:30:16Catalysts speed up chemical reactions
0:30:16 > 0:30:19without being used up or chemically changed.
0:30:19 > 0:30:23Enzymes speed up reactions - they make things happen quicker.
0:30:23 > 0:30:25'In our bodies, hydrogen peroxide is broken down
0:30:25 > 0:30:27'by the enzyme called catalase.'
0:30:27 > 0:30:32Sorry, I don't do liver - I just, I don't like it.
0:30:32 > 0:30:35'What happens when the catalase in liver
0:30:35 > 0:30:37'comes into contact with hydrogen peroxide?
0:30:37 > 0:30:41'I've added some blue washing-up liquid,
0:30:41 > 0:30:44'which shows you the gases more clearly.'
0:30:44 > 0:30:48Liver is effective at breaking down the hydrogen peroxide.
0:30:48 > 0:30:51'And it does this by breaking it down into water and oxygen.'
0:30:51 > 0:30:55That is what we call an enzyme reaction,
0:30:55 > 0:30:59and it's caused by catalase in our liver. Thank you!
0:31:02 > 0:31:06Hydrogen peroxide has the molecular structure H202.
0:31:06 > 0:31:11Catalase splits it up into H20 and 02 - water and oxygen -
0:31:11 > 0:31:13but how does it work?
0:31:15 > 0:31:18Every enzyme has a place in which the molecule fits exactly.
0:31:18 > 0:31:20This is known as the active site.
0:31:20 > 0:31:23The active site of the catalase
0:31:23 > 0:31:26allows the hydrogen peroxide molecule to fit exactly.
0:31:26 > 0:31:30You could say the active site is like the ring of a bottle opener.
0:31:30 > 0:31:34The hydrogen peroxide molecule slots exactly into the active site,
0:31:34 > 0:31:38and it's that that splits up the molecule into oxygen and water -
0:31:38 > 0:31:42breaking up the dangerous hydrogen peroxide and making it safe.
0:31:42 > 0:31:45Good stuff, that liver!
0:31:47 > 0:31:52Time to inflict senseless violence on a defenceless jelly baby,
0:31:52 > 0:31:54to learn about...food as fuel!
0:31:54 > 0:31:57All living things are in an energy race.
0:31:57 > 0:32:00We have to keep getting enough food to fuel our bodies.
0:32:00 > 0:32:03But not quite this much!
0:32:03 > 0:32:07The food industry uses the word calories to describe
0:32:07 > 0:32:10how much energy is contained in food.
0:32:10 > 0:32:13But scientists prefer to use the word joules -
0:32:13 > 0:32:16let's see how many joules are in this jelly baby.
0:32:16 > 0:32:20Our body uses food like a steam train uses coal.
0:32:20 > 0:32:24As we break down our food, it releases the energy our body needs.
0:32:24 > 0:32:27This is respiration, and it happens in our cells.
0:32:27 > 0:32:31We can look at how this works in the lab, by reacting our food
0:32:31 > 0:32:34with potassium chlorate, a powerful oxidising agent.
0:32:34 > 0:32:39According to the packet, one jelly baby contains 90 kilojoules.
0:32:41 > 0:32:45Let's see what 90 kilojoules of energy looks like
0:32:45 > 0:32:47when we release it in 10 seconds.
0:32:51 > 0:32:54So, let's give it a go...
0:33:06 > 0:33:0990,000 joules released in 10 seconds.
0:33:09 > 0:33:13'A reaction similar to this is going on inside our own bodies
0:33:13 > 0:33:18'when we eat a jelly baby - just a lot slower and a lot less intense.
0:33:18 > 0:33:21'The cells in our bodies release the energy from the jelly baby
0:33:21 > 0:33:25'by combining it with oxygen that we breathe.
0:33:25 > 0:33:27'This is aerobic respiration.
0:33:27 > 0:33:30'Aerobic respiration is a chemical reaction.
0:33:30 > 0:33:34'If you've ever wondered how we calculate how many calories
0:33:34 > 0:33:37'there is in food, it's probably because someone somewhere
0:33:37 > 0:33:41'has been burning it and measuring the joules of energy released.
0:33:41 > 0:33:45'If every jelly baby has 90 kilojoules, this means
0:33:45 > 0:33:49'there's a lot of energy in this trolley, which is a good thing...'
0:33:49 > 0:33:54..considering we need about 11,000 kilojoules a day.
0:34:02 > 0:34:05Do you remember that guy who had an apple fall on his head?
0:34:05 > 0:34:09Lies! He only saw it fall! Isaac Newton and his 1st Law.
0:34:11 > 0:34:14Ever since we invented the wheel,
0:34:14 > 0:34:16humans have been moving around faster and faster.
0:34:18 > 0:34:21More than 300 years ago, a guy called Isaac Newton
0:34:21 > 0:34:24came up with three laws about how things move.
0:34:24 > 0:34:29The first law is that a body will continue in a state of rest
0:34:29 > 0:34:31or uniform unaccelerated motion
0:34:31 > 0:34:34unless acted upon by some external force.
0:34:34 > 0:34:36So what's that all about?
0:34:42 > 0:34:45For a body to be at rest, the forces need to be balanced.
0:34:45 > 0:34:49Here, the boarders are trying to be at a state of rest.
0:34:49 > 0:34:52Some of them are better than others!
0:34:52 > 0:34:54When they DO manage it, their forces are balanced.
0:34:54 > 0:34:57The weight of the boarder is balanced
0:34:57 > 0:34:59against the force acting up through the board.
0:34:59 > 0:35:03So we've seen bodies at rest, but what exactly happens
0:35:03 > 0:35:07when a body is in motion? Well, the forces are still in balance.
0:35:07 > 0:35:11To go at a constant velocity, the force from the boarder's leg
0:35:11 > 0:35:16must balance the opposing forces of friction and air resistance.
0:35:16 > 0:35:19Here, the skater is moving at a constant velocity.
0:35:19 > 0:35:23The force from his legs is balanced against the forces of air resistance
0:35:23 > 0:35:24and the friction from the ice.
0:35:24 > 0:35:28Because there is no force of gravity on this ball in space,
0:35:28 > 0:35:33it continues in a perfectly straight line until it hits a wall.
0:35:33 > 0:35:37If forces are not balanced, the velocity will not be constant.
0:35:37 > 0:35:40When the boarder stops pushing with his leg,
0:35:40 > 0:35:43friction and air resistance win the battle,
0:35:43 > 0:35:45and the boarder decelerates.
0:35:45 > 0:35:49Equally, when the boarder needs to accelerate to do a trick,
0:35:49 > 0:35:52the forces are not balanced - he is applying
0:35:52 > 0:35:54a greater force than the opposing friction.
0:35:54 > 0:35:57Well, that's what he would like to do anyway!
0:36:00 > 0:36:04Force = mass x acceleration. Well, that was easy!
0:36:04 > 0:36:07So, onto number seven - yep, you guessed it,
0:36:07 > 0:36:09it's Newton's Third Law.
0:36:12 > 0:36:17These skateboards are great examples of how things move.
0:36:21 > 0:36:25Newton's Third Law states that if a body A exerts a force on a body B,
0:36:25 > 0:36:30then B will exert an equal, opposite force on body A.
0:36:30 > 0:36:34Body A and body B - better know as Phil and Oli -
0:36:34 > 0:36:37can you exert a force on Oli please, Phil?
0:36:37 > 0:36:40'This force gives them the same initial acceleration,
0:36:40 > 0:36:43'and once they've parted company,
0:36:43 > 0:36:46'they move off at the same speed, in opposite directions.'
0:36:46 > 0:36:48That's because the force exerted by A
0:36:48 > 0:36:50had an equal and opposite reaction.
0:36:50 > 0:36:52'When Phil pushes Oli,
0:36:52 > 0:36:56'there is an equal and opposite force that pushes Phil back.
0:36:56 > 0:36:59'Newton's Second Law states that for any force applied on an object,
0:36:59 > 0:37:03'acceleration is inversely proportional to the object's mass.
0:37:03 > 0:37:06'So here, because Phil and Oli are roughly the same mass,
0:37:06 > 0:37:08'assuming friction is a constant,
0:37:08 > 0:37:11'this force provides them with the same initial acceleration,
0:37:11 > 0:37:15'making them travel a similar distance from their starting point.
0:37:15 > 0:37:19'How would increasing the mass on one board affect acceleration?'
0:37:19 > 0:37:22We're going to bring in another skater. Martin, if you can step in?
0:37:22 > 0:37:24All right, guys?
0:37:28 > 0:37:32'They did both move away, but this time the board with two skaters
0:37:32 > 0:37:35'didn't move away with as much initial acceleration
0:37:35 > 0:37:38'as the board carrying one skater - so what's happening?'
0:37:38 > 0:37:41When Phil pushes against Oli and Martin,
0:37:41 > 0:37:44Oli and Martin push back with the same force,
0:37:44 > 0:37:46but in the opposite direction.
0:37:46 > 0:37:50Remembering Newton's Second Law, their initial acceleration
0:37:50 > 0:37:53will be inversely proportional to their mass,
0:37:53 > 0:37:56and because Oli and Martin are about twice the mass of Phil,
0:37:56 > 0:37:58assuming friction is a constant,
0:37:58 > 0:38:02the force can only accelerate Oli and Martin half as much as Phil.
0:38:02 > 0:38:06So Phil travels twice the distance in the same time.
0:38:06 > 0:38:11This is exactly the same principle that gets rockets into space.
0:38:11 > 0:38:15Newton's Third Law can help us to understand
0:38:15 > 0:38:19how we can change this plastic bottle into a water rocket.
0:38:29 > 0:38:33When I first start pumping, the increasing air pressure
0:38:33 > 0:38:37pushing down on the water is being held back by the bung.
0:38:37 > 0:38:39But as the pressure increases, eventually it's
0:38:39 > 0:38:43too much for the bung, and the water comes out with a huge force.
0:38:43 > 0:38:47This is where Newton's Third Law comes in.
0:38:47 > 0:38:50The rocket exerts a force on the water, pushing it downwards.
0:38:50 > 0:38:53The water exerts an equal but opposite force on the rocket,
0:38:53 > 0:38:55pushing it upwards.
0:38:55 > 0:38:59This is exactly the same principle that gets rockets into space.
0:38:59 > 0:39:02The burning fuel is forced downwards -
0:39:02 > 0:39:05it exerts an equal but opposite force on the rocket,
0:39:05 > 0:39:07forcing it upwards.
0:39:14 > 0:39:18You can solve the biggest problems with small solutions.
0:39:18 > 0:39:21And to feed the world, you've got to start with seeds -
0:39:21 > 0:39:23it's germination at number six.
0:39:23 > 0:39:27Germination is the process by which a plant begins to grow from a seed.
0:39:27 > 0:39:31Seeds need certain conditions to germinate successfully.
0:39:31 > 0:39:34Doctor Laura Bowden is a seed specialist, and I've asked her
0:39:34 > 0:39:38to try and germinate crop seeds for us in different conditions.
0:39:38 > 0:39:40Well, these are barley seeds,
0:39:40 > 0:39:44and these ones I grew in our controlled temperature room,
0:39:44 > 0:39:47which is at 20 degrees, so they've been nice and warm.
0:39:47 > 0:39:50These ones have been in the fridge
0:39:50 > 0:39:53at four degrees, so they haven't germinated at all,
0:39:53 > 0:39:57there's quite a difference, showing that temperature really is
0:39:57 > 0:40:00very important to seed germination.
0:40:00 > 0:40:03So we've seen that warmth is essential for germination,
0:40:03 > 0:40:05but there are two other crucial factors.
0:40:05 > 0:40:10Water is probably the most important factor for germination.
0:40:10 > 0:40:14Without water, most seeds can't germinate.
0:40:14 > 0:40:18In hotter parts of the world, the lack of water is a serious problem.
0:40:18 > 0:40:23Droughts can result in crops dying, causing terrible starvation.
0:40:23 > 0:40:26This experiment here, these are rye grass seeds.
0:40:26 > 0:40:31These ones have had a good amount of water - enough for them to grow well.
0:40:31 > 0:40:35These ones here haven't had quite as much water, so they're
0:40:35 > 0:40:39looking unhealthier. These poor ones have had no water at all.
0:40:39 > 0:40:42If you give them too much water, that would also be
0:40:42 > 0:40:45a stress and they wouldn't be able to go cope and it would kill them.
0:40:45 > 0:40:49We've seen that warmth and water are essential for germination,
0:40:49 > 0:40:51but there is one other crucial factor.
0:40:51 > 0:40:55Oxygen is very important. They need oxygen because they have to respire.
0:40:55 > 0:40:59Seeds contain a food store. Respiration requires oxygen,
0:40:59 > 0:41:03and releases energy from the food store.
0:41:03 > 0:41:06This is why seeds need oxygen during germination.
0:41:06 > 0:41:10Once the young plant has leaves, it no longer needs its food store
0:41:10 > 0:41:14because it makes glucose in its leaves by photosynthesis.
0:41:14 > 0:41:17Respiration then releases the energy needed from this glucose.
0:41:17 > 0:41:22So these are the basic factors that seeds need to germinate...
0:41:23 > 0:41:27But to have any chance at solving the world's food shortages,
0:41:27 > 0:41:30scientist are helping farmers work out the best ways
0:41:30 > 0:41:32of getting their crops to grow quickly.
0:41:32 > 0:41:36Quite often, farmers will apply fertilisers to their fields,
0:41:36 > 0:41:39which will speed up germination and plant growth.
0:41:39 > 0:41:41So these are grass seeds again,
0:41:41 > 0:41:46and these ones have had nitrate added to the solution that they're given
0:41:46 > 0:41:50to grow with, and these ones haven't, they've just had water.
0:41:50 > 0:41:54And you can see there is a huge difference in the growth.
0:41:54 > 0:41:58These ones, they have started to germinate, you can see the shoots,
0:41:58 > 0:42:00but they're so much smaller,
0:42:00 > 0:42:03and that's because of the effect of nitrates,
0:42:03 > 0:42:06which is the major component of fertiliser -
0:42:06 > 0:42:08so farmers use exactly this principle.
0:42:08 > 0:42:11Wow, that really is impressive.
0:42:13 > 0:42:17The research that Dr Bowden and her colleagues are doing
0:42:17 > 0:42:21is crucial to understanding how to improve our farming techniques.
0:42:21 > 0:42:24In 2011, the world population hit 7 billion,
0:42:24 > 0:42:28and by 2050, that number will be 9 billion -
0:42:28 > 0:42:319 billion people need an awful lot of food.
0:42:31 > 0:42:34Science is helping us understand more and more
0:42:34 > 0:42:36about how plants grow and germinate.
0:42:36 > 0:42:38And it's helping us to understand
0:42:38 > 0:42:41how we can feed our ever-expanding population.
0:42:41 > 0:42:43Get in line for more skateboarding tricks -
0:42:43 > 0:42:47putting the "sick" into physics! Time to create some friction!
0:42:47 > 0:42:50So now, we're going to talk a bit about friction.
0:42:50 > 0:42:53Any time one surface moves over another,
0:42:53 > 0:42:57there is a force of friction. Friction is a force
0:42:57 > 0:43:00that always acts in the opposite direction to movement.
0:43:00 > 0:43:03Here, the force of friction
0:43:03 > 0:43:06is opposing the motion of the skateboard.
0:43:06 > 0:43:10We spend a whole lot of time battling with friction.
0:43:12 > 0:43:15Friction can be a surprisingly strong force.
0:43:15 > 0:43:18Try this next experiment for yourself -
0:43:18 > 0:43:21fan the pages of two books together.
0:43:21 > 0:43:23I've got a challenge for you.
0:43:23 > 0:43:27I want to see if you can pull these two interleaved books apart.
0:43:31 > 0:43:33- Oh!- Oh, is it...?!
0:43:33 > 0:43:37- It's still not working, is it? - LAUGHTER
0:43:37 > 0:43:41So, why is it so hard to pull the books apart?
0:43:41 > 0:43:44Well, it's down to friction.
0:43:44 > 0:43:48Friction is caused by two things - at a microscopic level,
0:43:48 > 0:43:52the surfaces are uneven and therefore lock into one another.
0:43:52 > 0:43:54And also, the molecules of the paper
0:43:54 > 0:43:57are very slightly attracted to one another.
0:43:57 > 0:44:01When we're talking about two pages, it's very easy to pull them apart.
0:44:01 > 0:44:05But when you add up all the friction resulting from
0:44:05 > 0:44:08300 pages being on top of each other, it's a different story.
0:44:10 > 0:44:14The force of friction is useful to us in all kinds of ways.
0:44:14 > 0:44:18The parachute here is creating air resistance, a kind of friction.
0:44:18 > 0:44:21It opposes the downward movement of the space capsule,
0:44:21 > 0:44:24slowing it down and creating a smoother landing.
0:44:24 > 0:44:29It provides the force that keeps the tyres of this car on the road.
0:44:30 > 0:44:33Replace tarmac with ice
0:44:33 > 0:44:37and the tyres can no longer grip the surface due to reduced friction.
0:44:38 > 0:44:40CRUNCH
0:44:40 > 0:44:41Next, I'm live and direct,
0:44:41 > 0:44:45dissolving things in liquids to demonstrate solubility.
0:44:45 > 0:44:48Oh man, I wouldn't mind a nice cup of tea -
0:44:48 > 0:44:51I've been talking for ages now!
0:44:51 > 0:44:53I've got a question for you guys. Do you think I can fit
0:44:53 > 0:44:57this length of polystyrene into this jar?
0:44:57 > 0:44:59- Yes.- No.
0:44:59 > 0:45:02No? Yeah? I like that - you lot have got some faith in me!
0:45:02 > 0:45:04Excellent.
0:45:04 > 0:45:06Right, this is what we're going to do...
0:45:06 > 0:45:09We're going to take this length of polystyrene
0:45:09 > 0:45:11and stick it into this Pyrex jug.
0:45:11 > 0:45:14But we're going to use something to help us do it.
0:45:14 > 0:45:19It's this stuff. It's called propanone, or acetone.
0:45:19 > 0:45:23We're going to dissolve this polystyrene into this.
0:45:23 > 0:45:27And when we dissolve it in, this will be called the solute,
0:45:27 > 0:45:30and this stuff, that does the dissolving,
0:45:30 > 0:45:32will be called the solvent.
0:45:34 > 0:45:39And when they're mixed together, they will be called a solution.
0:45:39 > 0:45:42You add a bit of the solvent...
0:45:45 > 0:45:47Something's happening.
0:45:50 > 0:45:54- GIGGLING - Slowly but surely,
0:45:54 > 0:45:56it's going in.
0:46:00 > 0:46:04So, remember, acetone's the stuff that you've actually got
0:46:04 > 0:46:07in nail varnish remover.
0:46:07 > 0:46:10Aw, yeah!
0:46:10 > 0:46:13- Swill that around. - Hurray!
0:46:13 > 0:46:17- One, two, three...! Magic! - Oh, yes.
0:46:17 > 0:46:19So there we have it,
0:46:19 > 0:46:24a whole polystyrene rod fitted into a little Pyrex jar.
0:46:27 > 0:46:31- Hi. Can I have two cups of tea, please?- Sure.
0:46:31 > 0:46:36'Solubility is a measure of how much solute can dissolve in a solvent.
0:46:36 > 0:46:40'The solubility of a solute in a solvent changes with temperature.
0:46:40 > 0:46:43'And importantly, it depends on whether the solute
0:46:43 > 0:46:47'is a gas or a solid. So, let's look at solids first.'
0:46:47 > 0:46:49Here we have two identical hot cups of tea.
0:46:49 > 0:46:51And we want to see how much sugar
0:46:51 > 0:46:55can be held in solution in these hot cups of tea.
0:46:59 > 0:47:04When no more sugar can dissolve, the solution is said to be saturated.
0:47:10 > 0:47:13I think that's getting just about saturated now.
0:47:16 > 0:47:20But the situation changes when the liquid is cooled down.
0:47:20 > 0:47:23Luckily, I've got a bit of dry ice here,
0:47:23 > 0:47:25and that should do the job perfectly.
0:47:25 > 0:47:30Dry ice is at a temperature of minus 78 degrees centigrade,
0:47:30 > 0:47:32so it's going to cool the water down.
0:47:36 > 0:47:39In this one a tiny bit of sugar has crystallised at the bottom
0:47:39 > 0:47:43because it's a bit cooler. But this one, look how much sugar
0:47:43 > 0:47:45is actually in the bottom.
0:47:46 > 0:47:50The sugar behaves like most solids - the solubility increases
0:47:50 > 0:47:52as the temperature of the solvent does.
0:47:52 > 0:47:55What's interesting about gases
0:47:55 > 0:47:58is that they behave in the opposite way to solids.
0:47:58 > 0:48:03The solubility of gases decreases as the temperature increases.
0:48:03 > 0:48:06I'm going to show you a neat trick.
0:48:09 > 0:48:12Check out these ice cubes.
0:48:12 > 0:48:15One set's lovely and clear,
0:48:15 > 0:48:18but the other one's pretty cloudy.
0:48:23 > 0:48:27It's all down to the solubility of gases in a liquid.
0:48:27 > 0:48:31So to make cloudy ice cubes, all we need to do is, take tap water
0:48:31 > 0:48:34and put it straight in.
0:48:37 > 0:48:40But if we want our ice cubes to be clear,
0:48:40 > 0:48:42you have to boil the water first.
0:48:43 > 0:48:47And here's why boiling the water makes a difference.
0:48:47 > 0:48:50At room temperature, the water contains a certain amount
0:48:50 > 0:48:52of dissolved gases from the air.
0:48:52 > 0:48:55The water straight from the tap creates cloudy ice cubes
0:48:55 > 0:48:59because these gases that were dissolved in the water
0:48:59 > 0:49:00form tiny bubbles in the ice.
0:49:00 > 0:49:03By heating the water to boiling point,
0:49:03 > 0:49:07we have decreased the solubility of the dissolved gases.
0:49:07 > 0:49:09They come out of the solution as bubbles
0:49:09 > 0:49:14and the remaining water has less gases dissolved, so is less cloudy.
0:49:17 > 0:49:21For a solution, the solubility of gases decreases
0:49:21 > 0:49:24as we increase the temperature.
0:49:33 > 0:49:37And now we uncover the secret world of photosynthesis,
0:49:37 > 0:49:39here in its natural habitat.
0:49:39 > 0:49:43Photosynthesis is one of the most important reactions on this planet.
0:49:43 > 0:49:47Let's have a look at the word... "Photo" means light,
0:49:47 > 0:49:51"synthesis" means to make - and that's exactly what it does.
0:49:51 > 0:49:56So, plants harness the energy from the sun to make food.
0:49:56 > 0:50:00Photosynthesis happens in the leaves of all green plants.
0:50:00 > 0:50:04Without photosynthesis there would be no oxygen in our atmosphere
0:50:04 > 0:50:06and life as we know it would not exist.
0:50:06 > 0:50:08It happens inside the chloroplasts,
0:50:08 > 0:50:11which are found in leaf cells and other green parts of the plant.
0:50:11 > 0:50:14Chloroplasts contain a substance called chlorophyll,
0:50:14 > 0:50:17which gives the plant its green colour.
0:50:17 > 0:50:20Chlorophyll absorbs sunlight and uses its energy
0:50:20 > 0:50:23to convert carbon dioxide and water into glucose.
0:50:24 > 0:50:26Oxygen is also produced.
0:50:47 > 0:50:49Time for a demo here.
0:50:50 > 0:50:53Here we have the aquatic plant named Cabomba.
0:50:53 > 0:50:54It's very fast at growing
0:50:54 > 0:50:57and particularly efficient at photosynthesizing.
0:50:57 > 0:50:59We're going to have a look at two things.
0:50:59 > 0:51:02First, the oxygen produced.
0:51:02 > 0:51:05If photosynthesis is happening,
0:51:05 > 0:51:07the gas collected in the tube over the last 30 minutes
0:51:07 > 0:51:09should be oxygen.
0:51:10 > 0:51:13If it is oxygen, it will re-light this glowing splint.
0:51:20 > 0:51:21Wicked!
0:51:21 > 0:51:23Second thing, light!
0:51:23 > 0:51:26The good thing about using underwater plants
0:51:26 > 0:51:28is that you can actually see the oxygen being produced.
0:51:28 > 0:51:32The amount of bubbles coming out of the stem of the plant
0:51:32 > 0:51:35are a good indication of the rate of photosynthesis.
0:51:35 > 0:51:38But what happens if we reduce the light intensity?
0:51:44 > 0:51:46It's practically stopped.
0:51:46 > 0:51:49See, without light photosynthesis can't happen.
0:51:49 > 0:51:52So you can imagine if you were to put this in a pitch black room,
0:51:52 > 0:51:56there would be no photosynthesis and hence no bubbles being released.
0:51:56 > 0:51:59So for photosynthesis to happen,
0:51:59 > 0:52:04we need water, carbon dioxide, chlorophyll and light.
0:52:13 > 0:52:16We've already seen that photosynthesis produces oxygen,
0:52:16 > 0:52:18but the other product is glucose.
0:52:18 > 0:52:23This glucose is the fuel plants need for energy and to grow.
0:52:23 > 0:52:25So, essentially, plants make their own food
0:52:25 > 0:52:27and in turn, animals rely on plants for their food.
0:52:29 > 0:52:32Animals get their food from plants by eating plants directly
0:52:32 > 0:52:35or by eating other animals that have already eaten plants.
0:52:35 > 0:52:39Plants are the most fundamental part of the food chain.
0:52:39 > 0:52:44Photosynthesis is essential to life on this planet for two main reasons.
0:52:44 > 0:52:46One is it provides us with oxygen,
0:52:46 > 0:52:52and the second is it harnesses the sun's light energy to produce food.
0:52:55 > 0:52:56Wooo-hooo!
0:52:58 > 0:53:02Some scary cultures now. Who knows what bacteria we're carrying around?
0:53:02 > 0:53:06Number two - microorganisms.
0:53:06 > 0:53:08Bacteria are a type of microorganism,
0:53:08 > 0:53:11each made up of just one cell.
0:53:12 > 0:53:15Some bacteria are harmful and cause disease...
0:53:15 > 0:53:19and some are useful, like the 100 trillion bacterial cells
0:53:19 > 0:53:22that inhabit our digestive system.
0:53:22 > 0:53:24Bacteria reproduce by cloning themselves
0:53:24 > 0:53:28through binary fission, a kind of asexual reproduction.
0:53:28 > 0:53:31In the right conditions, they can reproduce very quickly.
0:53:31 > 0:53:34Some species can replicate themselves
0:53:34 > 0:53:35in as little as 20 minutes.
0:53:35 > 0:53:40We can grow bacteria in an incubator on plates of agar jelly.
0:53:40 > 0:53:42With time, nutrients and an optimum temperature.
0:53:42 > 0:53:45These girls at Copthall to investigate the bacteria
0:53:45 > 0:53:47growing on their possessions.
0:53:47 > 0:53:52They took some Petri dishes and they swabbed some of their stuff.
0:53:56 > 0:53:58And put them in an incubator
0:53:58 > 0:54:01set at just under 30 degrees centigrade to help them grow.
0:54:01 > 0:54:03Two days have passed since we put
0:54:03 > 0:54:05the agar plates inside the incubator.
0:54:05 > 0:54:09So lets have a look what's been grown.
0:54:09 > 0:54:11With any scientific experiment, you need a control,
0:54:11 > 0:54:13- don't you?- GIRLS: Yeah.
0:54:13 > 0:54:16So, here was our control here.
0:54:16 > 0:54:18Whooo!
0:54:18 > 0:54:21Nothing at all.
0:54:21 > 0:54:25Brilliant. So there's proof that if you just shut one by itself,
0:54:25 > 0:54:27you'll have no bacteria.
0:54:27 > 0:54:29What've we got here?
0:54:29 > 0:54:33Headphones. Got a few speckles here and there.
0:54:33 > 0:54:35- GIRL: That's been in my ear! - That's not too bad.
0:54:35 > 0:54:37You've got a few different microorganisms in there.
0:54:37 > 0:54:39Earring.
0:54:40 > 0:54:42GIRLS: Eugh!
0:54:45 > 0:54:47You know what, I'm glad I don't wear earrings!
0:54:47 > 0:54:51So there's a lovely pattern being drawn with the earrings
0:54:51 > 0:54:52and you can see the bacteria have grown
0:54:52 > 0:54:54in exactly the same place as your pattern.
0:54:54 > 0:54:59So everyday objects harbour all types of bacteria
0:54:59 > 0:55:01and these can be grown in Petri dishes with some surprising
0:55:01 > 0:55:03and rather revolting results,
0:55:03 > 0:55:06as shown with the help of the girls at Copthall School.
0:55:06 > 0:55:08So finally, at number one,
0:55:08 > 0:55:13it's a really important subject about how oceans are turning acidic.
0:55:13 > 0:55:15It's acids and alkalis.
0:55:15 > 0:55:18We live on a blue planet. 70% of the Earth's surface
0:55:18 > 0:55:22is made up of oceans, and there's a problem.
0:55:22 > 0:55:24The oceans are changing.
0:55:24 > 0:55:27We know they're changing because their pH is changing.
0:55:27 > 0:55:29So what does this really mean?
0:55:29 > 0:55:33The pH of a solution is a measure of how acidic or alkaline it is.
0:55:33 > 0:55:35We can use a universal indicator
0:55:35 > 0:55:39to work out the pH levels of different solutions.
0:55:40 > 0:55:44If the solution goes green, then it's neutral.
0:55:44 > 0:55:49If the solution goes red, then it's very acidic.
0:55:49 > 0:55:55And if the solution goes purple, then it is very alkaline.
0:55:55 > 0:55:57In fact, if you go through the pH scale
0:55:57 > 0:55:59you can get all the colours of the rainbow!
0:56:06 > 0:56:10Different parts of the body need different pH levels
0:56:10 > 0:56:12to operate efficiently.
0:56:12 > 0:56:14The blood has a pH that is very slightly alkaline,
0:56:14 > 0:56:18while the stomach needs an acidic pH.
0:56:18 > 0:56:19It's the same for aquatic life.
0:56:19 > 0:56:22Oceans provide a pH between 7.8 and 8.4
0:56:22 > 0:56:25that aquatic life thrives in, but scientists are worried
0:56:25 > 0:56:30that the pH of our oceans is now becoming more acidic.
0:56:30 > 0:56:32Most scientists believe that this acidification is due
0:56:32 > 0:56:36to the CO2 that we are producing, being absorbed by the oceans.
0:56:36 > 0:56:39Professor Sella has prepared a simple demo to show
0:56:39 > 0:56:41what is happening to our oceans.
0:56:41 > 0:56:43The water in this jar has some universal indicator in it
0:56:43 > 0:56:45and we can use that to represent the ocean.
0:56:45 > 0:56:48We're going to put in a bit of alkali.
0:56:48 > 0:56:51First of all, Andrea adds some alkali
0:56:51 > 0:56:55so the solution now matches the pH of the ocean, around 8.1.
0:56:55 > 0:56:57Nice and purple. OK?
0:56:57 > 0:57:00And now we're going to add the carbon dioxide.
0:57:00 > 0:57:02Carbon dioxide is actually dry ice.
0:57:02 > 0:57:06It's going to bubble and bubble. Watch what happens to the pH.
0:57:06 > 0:57:10Boiling away, great effect.
0:57:10 > 0:57:12This is happening in our lifetime,
0:57:12 > 0:57:15and you can see it's already gone from purple...
0:57:15 > 0:57:17To me, its beginning to look blue-ish green.
0:57:17 > 0:57:20So we're gradually coming towards neutral,
0:57:20 > 0:57:21and if you wait a moment longer,
0:57:21 > 0:57:25it's gradually going paler and paler.
0:57:25 > 0:57:27We're really past the neutral point.
0:57:27 > 0:57:30We're actually into the acidic region.
0:57:30 > 0:57:33So as the carbon dioxide bubbles through the water,
0:57:33 > 0:57:35it's turning the water more acidic?
0:57:35 > 0:57:39Absolutely. What it's doing is making something called carbonic acid,
0:57:39 > 0:57:42and this is happening with our atmosphere
0:57:42 > 0:57:44much more slowly,
0:57:44 > 0:57:47as the CO2 dissolves in the oceans, becoming more acidic.
0:57:47 > 0:57:50There are really big questions about what happens
0:57:50 > 0:57:52to living things in the oceans.
0:57:52 > 0:57:57The oceans certainly should be just slightly alkaline,
0:57:57 > 0:58:01just away from neutral, and what's happening is that they're slowly
0:58:01 > 0:58:04moving down towards more acidic conditions.
0:58:06 > 0:58:11That's why the world needs scientists in the future,
0:58:11 > 0:58:13to help tackle some of these big changes to our planet.
0:58:17 > 0:58:21So there we have it, my Top 20 Demonstrations. Hope you enjoyed it!
0:58:21 > 0:58:24They're all online at...
0:58:24 > 0:58:26..including some extra ones!
0:58:26 > 0:58:30And, of course, the full-length version of my photosynthesis rap!
0:59:05 > 0:59:09Subtitles by Red Bee Media Ltd