In order to get a floating balloon you want a gas which is as light as possible.  Helium is quite a lot lighter than air weight.  It’s about and eighth of the density of air.  Hydrogen is about a sixteenth the density of air.  So it’ll float in air and will even float upwards. You’d have thought that hydrogen would be a better gas as it would give slightly more lift than helium because it’s lighter.  This is true.  The problem is hydrogen is explosive and if you have children running around with balloons that could catch fire and blow up in their faces, it may have some health and safety implications.  The other thing is that although hydrogen is half as heavy as helium it doesn’t give you twice as much lift because the amount of lift you get is in its difference in density with [respect to] air.  It’s actually only another sixteenth of the density of air.  It’s a little bit better but not very much, so it’s not worth the danger.

Helium is quite expensive, though, because it’s a limited resource here on the planet. It's only created by radioactive decay on Earth.  Atomic nucleuses emitting alpha particles that are actually helium nucleuses.  They slow down and gain some electrons and turn into a helium atom.  It tends to be found in oil wells where you get a gas-proof layer of rock above a load of rocks containing radioactive elements.  They break down to helium.  It floats up and gets trapped, often at the top of an oil well . The amount of helium that we can access cheaply is very limited because not all our oil wells have it.

It is true, we are passengers in our own body.  In fact, 10 is a conservative estimate.  There are 50X more bacterial cells living in you and on you than there are cells in the rest of your body that are you.

Most of them are in the gut, of course, the intestines.  We have them there because we have the perfect place for them to live.  There’s lots of things for them to eat; there’s lots of gases which they can metabolise.  Most of our insides are devoid of oxygen, for example, and lots of these bugs are anaerobes (they don’t like oxygen).  They do us a lot of favours and by having them there they’re taking up resources and space which potentially nasty bacteria could take up.  By having lots of these bugs in us they’re in fact protecting us from being infected.  When you go abroad and get diarrhoea what’s actually happening is that the local bugs are combating your friendly bugs and beating them off for a while.  Your body then learns to react and pushes the nasty ones back out so the friendly ones can re-colonise.

Bacteria are roughly a tenth of the size, or smaller, than a human cell.  In fact, if you look inside a human cell you can see evidence of evolution because there are these structures called mitochondria.  Mitochondria are the cellular powerhouses.  The mitochondria are the same size as a bacterium and scientists think they look so similar because way back in evolution a bacterium got inside an early cell.  The two developed this partnership called the Symbiosis Theory and the bacterium lots of energy but the cell gave the bacterium protection and things it needed.  The consequence was the two things lived happily side by side.  But we’re still living side-by-side with bacteria.  We need them and if we don’t have them in our guts then we’re less healthy for the simple reason that if you rear animals and they’re not allowed to have bacteria in their guts they don’t do very well. This can mean that taking antibiotics may have negative effects.  When you take antibiotics that are ‘broad-spectrum’ antibiotics these go through you like Domestos and kill the good bacteria.  Anything that’s left behind that’s not vulnerable to the effect of antibiotic can then over grow.  Yeasts and other fungi infections can do that because antibiotics won’t kill those but they will kill the bacteria.  Things like Clostridium difficiles, C. diff which leads to antibiotic associated diarrhoea and kills people in hospital.  If people are but on heavy dose antibiotics then all the friendly bacteria get wiped out and these other ones over grow. It can be a big problem.

It does sound very strange, doesn’t it?

They don’t want to use actual contacts because in a wet environment like a bathroom the contacts will get dirty. They’ll rust and they won’t last very long. What they do is something else which is kinda cunning.

Inside that little protuberance there’s a coil of wire which connects to the mains.  Basically you’ve got a current running backwards and forwards through that wire, and that produces a magnetic field.  It’s an electromagnet so it’s a magnetic field that’s going one way and then another.  Inside the toothbrush is another coil going outside the protuberance, again, under the plastic going round and round then connecting to the toothbrush itself.  If you have a changing magnetic field going near a conductor the field will induce a current in that conductor.  It’s actually how a transformer works. The current inside the first coil makes a changing magnetic field and that makes a current flow inside the second coil without having to touch it.  That charges the toothbrush itself.

This takes advantage of the fact that although electricity will not travel through the plastic, magnetism will!

Ryan is probably wearing what’s called polarised sunglasses.  What they do is they only let one polarisation of light through.  Light is a wave and can be thought of as a bit like a piece of string.  So if I had a piece of string between me and you there I could probably loosen it by wobbling it up and down and that would make the waves move vertically.  I would call that vertically-polarised light.  Or I can make waves by wobbling it horizontally and that would be called horizontally polarised light.

Light can be either of these, or any other polarisation in between.  In fact, light coming from a normal light bulb or a fluorescent tube or the sun has all of them mixed together. Every possible polarisation.

Then you get things called polaroids which your sunglasses are. These will only let one polarisation through. If you have them horizontally it will only let horizontal through or vertical will only let vertical through.  If you’ve got two of them, if they’re both horizontal light can get through it because light can get through the first one and the second one. If you rotate the second one to vertical nothing will get through because the first one stops horizontal and the second one stops vertical.

LCD's use this because they have polarisers on them. Light comes though from underneath and gets polarised so only the vertical is coming through.  Then you have something called Liquid Crystals which can twist the polarisation of light by 90 degrees: they are set up so light can get through normally.  But if you then apply an electric field to it, the crystals stop twisting the polarisation so no light will get through and it’ll go black.  This means the light coming out of the LCD (Liquid Crystal Display) is polarised in only one polarisation so if your sunglasses are orientated in the right way it can block it and it’ll go blank.