Chris: So Martin’s ceiling rose almost became a shower rose, Dave.  Why didn’t it go bang?

Dave: Do you have a trip switch in your house?

Martin: I do have fuses, yeah.

Dave: Oh.  Fuses are just things which will break if you draw too much current.  Have you got one of the trip switches, sort of residual current devices which will trip if any current’s going to earth?

Martin: No.

Dave: Ok.  If you haven’t got a trip switch the only thing which is going to cause the electricity to turn off is if you’re drawing more current than one of the fuses can take so that would involve more than 40 or 50 amps of current.  As long as there’s less current going through the water than forty of fifty amps then your house just thinks someone’s plugged in a whole load of lights so maybe a heater in your ceiling rose.  If you did have a trip switch and the water was connected to something earth like a water pipe or central heating system to the earth then the trip switch would detect that there was some current running from the mains to the earth down the earth wire.  A trip switch would think oh no, something’s wrong maybe the central heating system’s exploded, we’ll turn the power off now.  Without a trip switch there’s no reason why your power shouldn’t carry on.

Chris: These lights are definitely not 12V, are they?

Martin: I’ve not got a clue.

Chris: Because one of the other fancy things that people tend to do in kitchens and other places round the house is that they tend to have a 12 volt system running those little mini halogen lights.  They’re very, very bright because all they do is draw a much bigger current but at a lower voltage.  Because water isn’t a terrifically good conductor like Dave said then at 12 volts it often won’t actually make that much difference because there’s not a big enough potential difference to flow the current through the water.  So if it's 12 volts, that may be why it didn’t go bang.

It’s not really a question of the animal knowing what to evolve into but this is a really beautiful example of evolution in action: mimicking the surroundings so animals are well-hidden and protected from predators.  A particular species of seahorse will find a good bit of seaweed to actually hide amongst and gather food in a really nice place for it to live.  As the seahorses breed and as new generations of seahorses are born small genetic mutations will change their appearance and change certain things about them.  As their appearance changes you might get a mutation that makes them a slightly different colour that’s similar to the seaweed, for example.  A seahorse that’s a very similar colour to the surrounding seaweed would be better protected because it would be camouflaged much better so hidden from predators.  More of those colours, of course, would survive so eventually all of the seahorses would eventually resemble the habitat in which they live.

Other animals have evolved other ways to disguise themselves - with some disguises making them look poisonous, to put predators off.

Connie was referring to the news story about "GOAT" (ghrelin O-acyltransferase), which adds a  carbon chain to the hormone ghrelin.  Ghrelin is produced by the stomach and stimulates appetite, so targeting it could help develop anti-obesity drugs.

That’s a very good suggestion and I suspect the answer is yes.  Researchers are eager to find ways to help people who have eating disorders and increase their ability to take onboard food.  I don’t know if it’s actually been trialled though, in the context of people who have an eating disorder.  I think it’s just healthy volunteers they’ve tried it on so far but it’s a very good point and yes you could make a case for doing that because people are often surprised to learn that the class of psychiatric condition which is associated with the highest rate of suicide and death is not all the things like schizophrenia and bipolar disorder (manic depression) although they have a very high suicide rate, the rate of death is actually highest amongst people with eating disorders.  Anorexia Nervosa, is I believe, associated with more people dying than virtually any other condition.  Certainly in young people it’s a leading cause of death.  Anything that can be done to help them is a really big step forward.

We also had this comment from Rachel in Cambridge:

In eating disorders appetite isn’t the driving force behind them.  A drug that stimulates appetite might therefore not help because the problem is not a lack of desire to eat but actually not allowing yourself to eat.

The thing that’s going on when you blow on your hand is you tend to blow on it from far away.  Especially if you’re blowing with pursed lips.  If you breathe slowly, especially if you’re close, then all the air to your hand is the nice warm air from your lungs.  When you’re blowing on them with pursed lips, partly it’s going to be further away so the air will be cooled down a bit more.  Also, as you’re farther away it will tend to catch cold air from the surroundings and drag that along with it.  You’re not just blowing along through your lips there’s also a load of cold air mixed in.  Also, the faster the air’s moving the more you’ll tend to evaporate moisture from your skin which will cool you down as well.  I think if you’re blowing with a big fan very close to your windscreen which is the way it works the higher the fan is the more it will defrost your window.

You’ll notice the waves are in time with the beating of your heart so there’s a pulse.

What happens when you cut yourself, inflammatory chemicals are sent to that part of your body where it’s part of your body’s defence to prevent infection to that wound.  Some of those chemicals stimulate nerve endings, nerve endings that are sensory receptors that are mechanically stimulated.  As your artery throbs with the beat of your heart that stimulates those sensitised nerve endings and you get this throbbing, beating pain.

Roy was referring to this news story about an underwater thermal glider.  Designed to take advantage of changes in temperature to glide long distances collecting information about the sea bed.

You couldn’t have a person in this type of glider because of the amount of energy you need to keep the person going; you need to keep them warm and give them oxygen.  It would be far more than the energy you could generate.  So you’d have little, tiny computer-controlled things which can just travel through the ocean all over the place.  In fact the biggest limitation on it is the amount of power it can use because it can’t generate very much.  You need to have not very power-hungry sensors.

First of all 99% of the world just has 2 tides a day and the reason for that is basically the moon and the sun pull on the Earth and on the water around it.  If you’re close to something massive it’s got a stronger attraction due to gravity than something farther away.  Water on the side of the Earth closest to the moon is going to get pulled the hardest and the Earth which is in the middle is doing to get pulled slightly less hard and the water on the far side is going to get pulled even less hard.  So you tend to get two bulges of water: one is the bulge of water close to the moon and the other bulge of water on the other side which is getting left behind.  That’s the reason why most places get 2 tides a day.

Some places get 4 – the only place I know about it is Southampton, Portsmouth in the UK by the Isle of Wight.  If you look very closely at the map of the Isle of Wight it has funnels on each side of the channel just north of it.  As the water rushes up the channel it sort of piles into these funnels and then as it gets narrower the wave gets higher.  You actually get a high tide as the water rushes up.  You get another one on the other funnel as the water rushes back down the channel so you get twice as many tides as you should have.

That’s because when you stand up all of the blood which is circulating round the body suddenly has this big force of gravity pushing it straight down into your legs.  The amount of blood coming back up from your legs into you heart to be pumped out into your brain drops.  Your retina, the part of the eye that converts light into signals that the brain can understand has the highest metabolic rate of any tissue in the body so if the blood flow to the retina drops very, very slightly for a fraction of a second it starts to fire off abnormal signals.  Those are the white lights that you see.