illuminating science

In what is sure to add to the growing debate about embryos, stem cells and abortion, though no less impressive because of it, scientists have used retina cells from aborted fetuses to cure retinitis pigmentosa, the leading cause of blindness in “rich” countries. They harvested (which I think is a most unfortunate choice of terminology) sheets of retinal cells from donated fetuses, and it seems that the effect is long term.

Note that this is very different from using stem cells, as the latter come from embryos (the first stage of cell division, where no specific retina cells yet exist) and haven’t yet been shown to cure this type of disease. New Scientist is well aware of how sensitive an issue this is - they don’t mention where the cells come from until halfway through the article. As they point out, if this treatment becomes accepted, then there’s going to be far more patients than donated fetuses available, so the group is considering transplanting the retinal cells from pigs instead. Of course, this has its objectors as well!

My weekend hiatus begins now, as I’m off to the Londong Balboa Festival for the weekend - very exciting! Only two weeks left in the UK, too! See you all on Monday.

Sean Carroll has a really interesting post about a paper he’s written on cosmology and the arrow of time. The “arrow of time” refers to the idea that even though most microscopic physics (e.g., single particles and quantum mechanics) looks the same whether time runs forwards or backwards, macroscopic physics (e.g, smashing a plate or cooling a cup of coffee) has a definite “direction” for time to flow. So, while I could run a movie of a single electron forwards or backwards, and you couldn’t tell the difference, you’d probably realise something was wrong if fragments of broken china suddenly formed into a whole plate! The arrow of time exists because of entropy (basically the “disorder” of a system) and the second law of thermodynamics which says that entropy always increases. So, in our example, a broken plate is more disordered than a whole one, so for it to spontaneously fix itself would decrease entropy, which is not allowed.

His paper is about explaining why our universe started off with low entropy, how inflation of the universe fits into the picture and how (on a really big scale) the whole universe may look the same whether run forwards or backwards. His summary (in his post) is really quite good (with lots of links for the uninitiated) so I won’t say any more - go and have a read! If you’re feeling adventurous, you can even get a sneak preview of his paper before the rest of the physics world.

A few more links added to the blogroll today. Check out Sean Carroll’s Preposterous Universe for some interesting article on physics and cosmology (and politics as well!) including a very nice cosmology primer. If you’re interested in string theory, two interesting blogs are Not Even Wrong and Luboš Motl’s reference frame which are two quite opposing views on string theory, and have some interesting discussions and posts going back and forward. Just so you know, both use quite a bit of physics in their posts, so you might sometimes find it a little tough going if you’re not up with the jargon!

And finally, Electron Blue is by an artist with an interest in science, such as creating artwork using logarithmic spirals.

Feeling a bit tongue tied? Just run a small current (2 thousandths of an ampere, less than what’s powering your watch) across the front of your head, and improve your verbal skills!

Volunteers were asked to name as many words as they could starting with a given letter in 90 seconds. Those with a current flowing (everyone was hooked up, but some were unknowingly controls) showed a 20% increase in the number of words they could supply. The rough theory is that the current stimulates the prefrontal cortex, associated with word generation, letting the neurons fire more easily and making the area more active. I wonder how long before AA batteries are banned in exams?

Okay, this is definitely in the “Woah.” category (as Neo would say.) Scientists from the University of Florida have grown neurons taken from rats in a Petri dish to create a “live computation device”, capable of flying a plane! Grown over a grid of electrodes, the neurons grew connections between them and were trained to be able to interpret signals (current status, weather, etc) coming from a simulated (simplified) plane flight and respond by sending the correct directions to the plane’s “controls” (e.g., controlling the pitch and roll of the plane.)

Neural networks have long been seen as a way of getting computers to handle the comlex tasks (such as face or letter recognition) that are so easy for humans and yet so hard for machines. Normally, these are simulated in software - but these guys are using the real deal, biological neurons.

Applications include uncrewed planes (perhaps both commercial and military), the ability to study and perhaps simulate epilepsy in a controlled environment, and testing drugs. Before you panic, though, these “hybrots” (HYBRid robOTS) contain only 25,000 neurons, compared to billions for a real brain, and lack complex structure - they’re nowhere like advanced enough yet to pilot a real-world plane (nor take over the world SkyNet style!) But as these “brains-in-a-dish” become more advanced, it may well raise some interesting questions about the nature of conciousness, and how complicated a neural network has to be before you would consider it a “brain”. Might we ever need to consider the “rights” of computers with organic brains? I don’t think it’s every going to come to that, but it’s food for thought.

Researchers have confirmed, in the journal Nature, one of General Relativity’s last unproven predictions - that of frame dragging, which says that a spinning object (like Earth) bends and warps space-time around it. To understand this, imagine twirling a spoon in a cup of coffee, or better yet, putting a spinning top in honey. The water or honey would twist a little bit, following the spinner, and anything floating on the surface would be dragged with it. In the same way, two satellites in orbit around Earth were found to be dragged off course by about 2 metres a year. (Just for the record, this probably has nothing to do with the Pioneer anomaly mentioned a couple of days ago.)

You might recall (if you are a devoted reader!) that I posted a couple of months ago on gravity probe B which is a satellite that’s testing the same theory, but with gyroscopes. Despite being scooped by a low cost, ground based observation team (d’oh!) the Gravity Probe will still have an important role to play - some scientists are still skeptical of the accuracy of today’s findings. Gravity Probe B will give highly accurate and irrefutable results (hopefully positive results!) which will settle the debate once and for all. Only one prediction then remains to be proven - the existence of gravity waves. But that’s another post…

In an interesting and potentially scary study, a Swedish study has found that using a mobile phone for more than 10 years doubles your chances of getting a benign type of head tumour. It sounds like the study does have good statistical backing (unlike many of these types of reports), in particular havingh a large sample size. Particularly impressive, is that the tumours seem to form on the side of the head where users claim they held their phones (although, as they point out, people with a tumour on one side might be more likely to say they held their phone there.) The research was part of INTERPHONE, an international effort to investigate mobile phones and related technology, with full reports to be released in 2005.

Keeping things in perspective, though, mobile phones seem unlikely to cause mass deaths. It does give us some interesting social questions, though. If it’s proved beyond doubt that mobile phones are linked to benign tumours, would you change your habits? (Note that hands free kits may or may not reduce exposure.) What if it increased your chance of a malignant tumour by 1%? Or by 5%, over your whole life? Would you stop using your mobile? Even more generally - what risks would you be prepared to take in order to keep using your mobile phone?

Oh, and I’m off to Ireland for the weekend, so there won’t be any posts for a couple of days. If you need to contact me, I’ll have my mobile on…

Interesting story on the Pioneer spacecraft (numbers 10 and 11, launched 30 years ago), no longer being where they’re supposed to be. Through very precise and careful calculations of all the effects of gravity, solar wind and onboard thrust, scientists say the craft “should be” about 400,000km (the distance from Earth to the moon) from where they are now.

While the most likely cause is simply an unexpected on-board effect, such as the ships giving off extra heat or gas (and kudos to the reporter for making this clear in the article, and not sensationalising things!) it is possible that something more interesting is in play. Possibilities include dark matter in our solar system, or even an unkown feature of gravity. The European Space Agency may well fund a “mission to explore the Pioneer anomaly”. Because even though the explanation is likely to be mundane, if it’s not then it’s a big thing for physics! It won’t be till 2015, though - so don’t get your hopes up yet.

In my last post I talked about perceptual rivalry and showed you some of Jack Pettigrew’s demonstrations. So, how do we explain what’s going on here? Jack Pettigrew’s theory is that the two hemispheres of our brain are competing for control of interpreting the image; that when we see one image, it’s the left hemisphere, when we see the other, it’s the right. This is called interhemispheric switching. There is already evidence for this - try breathing through your nose while blocking first one nostril and then the other; you’ll find that one is blocked and one is clear (approximately, and assuming you don’t have a cold!) Now, try this every hour - you’ll find that the open nostril will oscillate back and forwards over a few hours. It’s an example of interhemispheric switching - each hemisphere controls one nostril! (Remember that each hemisphere is responsible for the opposite side of your body, e.g., your left hemisphere controls your right hand. ) The nostril switching was apparently known to ancient mystics! An even more amazing example is the Sandlance fish. Each hemisphere of its brain controls an eye, but the eyes always move in alternation, never at the same time. Control is being passed back and forwards between the hemispheres! And you can easily see this for yourself.

Jack’s got some pretty strong evidence to back up his claims for the connection between interhemsipheric switching and rivalry . In his lab (where volunteers, or just the curious, are always welcome!) subjects watch perceptual rivalry demonstrations (similar to, but more complex and controlled than, the ones on the web) and push a button every time their view changes. As soon as they do, he then either pumps one of their ears full of icy water (which has the beautiful technical term “caloric vestibular stimulation”) or applies a sudden magnetic field to one side of their head. (Yep, volunteers always welcome!) The subject then “locks” towards one perception over the other, undoing the switch immediately if need be, and stimulating the other side of the head would lock to the other perception!

What’s even more amazing is that if interhemispheric switching really is occuring, then it must play a part in high level brain functions, such as mood and motivation. And again, this theory holds up - people with bipolar disorder have a much longer “switching times” between the two perceptions than the average. This has been repeatedly demonstrated by experiments. Jack Pettigrew’s theory is that people with bipolar disorder become “locked” into one side of the brain - the left hemisphere is associated with “positive” mood changes, while the right hemisphere with “negative”, corresponding to the manic and depressive mood swings. But can we use this information practically? You bet! In people in the mania phase, who they theorised were locked into the left hemisphere, they injected icy water into the left ear (as mentioned above) and the brain was shocked into stimulating some right hemisphere activity, and the mania was cured! Great quote: “One wonders whether the 50c syringe of cold water will catch on in the clinica”. In a “normal” person, you can even stimulate those moods by doing the same thing - the cold water temporarily “knocks out” one hemisphere, leaving the other in control - put icy water in someone’s left ear and their right hemisphere takes over, leaving them feeling depressed. Pump it in the other ear, and they’re in a fabulous euphoric mood!

This is only a small part of the research that Jack Pettigrew and his group are doing. He’s quite interested in Buddhism: he’s travelled around testing the perceptual rivalry switching time of Buddhist monks and the Dalai Lama and is designing and planning to run experiments to test Buddhist beliefs. Both are with the full support of the Dalai Lama, who actively encourages scientific research into his faith, and has repeatedly said that if anyone can demonstrate scientifically that one of their beliefs are false, then he will change their teachings immediately. A refreshing change!

I’ll write more on Jack Pettigrew in the futre, but to finish, here’s one more selection of my favourite demonstrations - this one is amazing (my favourite!), as is this one and this one.

I find neuroscience, the study of the brain and its functioning (e.g., this year’s Psychology Ig Nobel.) to be a fascinating topic. At the University of Queensland, we’re lucky enough to have Jack Pettigrew, an amazing scientist, who is researching (among other things) perceptual rivalry and interhemispheric switching. His website has a lot of information, so I’ll try and summarise what I know here, including things I learned from one of his talks.

Perceptual rivalry refers to the phenomena of being presented with an image which has two possible interpretations, but where you can only see one at a time. The simplest example is the Necker cube - which “side” is the top of the cube? You will probably see it switching from leaning to the left or to right, every few seconds. Try as you might, you probably won’t be able to see both at once! Jack Pettigrew has a tonne of demos on his site. A few of my favourites are:

• The reversible sphere - which way is it rolling? Keep watching! If you think there’s a trick, get a friend to watch with you, and you can both say which direction it’s going in and when it changes - bet you won’t always agree!
• An animated Necker cube
• Boneh’s Illusion - watch the blue dots, and see what happens to the yellow dots. Some or all of them should periodically disappear and reappear! If they don’t, “try again when you are in a “better mood” (disappearance increases with euphoria), or at a different time of day.” Some of his thoughts on it are .
• Dali’s Slave Market/Voltair. Can you see both of the title images? (hint: there’s a skull in one of them!)

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Next post will describe Jack Pettigrew’s theories of perceptual rivalry and interhemispheric switching!

Scientists from Queensland’s Institute of Medical Research has found that introducing crustaceans into water storage systems will destroy mosquito larvae carrying the potentially dengu fever.

The research was carried out in 41 Vietnamese communities, who have not seen a single case of dengue fever over the three years of the trial. (The limited article information says they would usually have “heaps” of cases per year.)

Quite a neat solution!

Got a spare five minutes? Or five hours? If so, then you should definitely check out 20Q.net. This is everyone’s favourite game (20 questions!) - but this time, you’re playing against the computer! By asking a series of, often bizaar, questions (”Does it bring you pleasure?” or “Will it fit in an envelope?” or, my favourite, “Is it heavier than a duck?”) it will guess the object you’re thinking! It’s a neural network, which actually learns from you as you play - so if you beat it once, you might not be so lucky again! (And you will beat it, sometimes - but it’s surprisingly good!)

It can handle carrots, love, quantum mechanics, and colours (but keep in mind that if you’re playing anonymously, it’s G-rated! You have to log in if you want to try more, ahem, “interesting” searches.) A hardwired, pocket version (presumably non learning) is now available (and guessed my word, “carrot”!)

Nothing has particularly caught my eye in the world of science today, so I thought I’d do a plug for one of my favourite internet resources: Wikipedia. This site is a gigantic, free, online encylopedia covering almost every topic imaginable. What’s brilliant about it is that anyone can contribute to it - if you know something that the Wikipedia doesn’t, you can add your own article! Now, while you might think this undermines the reliability of the material, remember that there are many, many people reading the encyclopedia - and if they see something wrong, they’ll fix it up. So very quickly, any inaccuracies from one person get smoothed over by the combined knowledge of the internet. I use it regularly - you’ve probably noticed that I constantly link to it in my articles, but I also use it when working on my thesis! It’s a great starting point to get an overview of a complex topic, and to get some ideas of what to Google for next.

The best way to search it is to do a Google search for “ wikipedia”, e.g., Quantum comoputer wikipedia returns the article on Quantum Computers. Alternatively, you can try just adding your topic to the end of http://en.wikipedia.org/wiki/, e.g., for Physics go to http://en.wikipedia.org/wiki/Physics. Just for fun, check out Crushing by elephants - something that’s NOT included in Encyclopedia Brittanica! And while Wikipedia is, and will alway be, free, it relies solely on public donations for funds (no advertising ont the site!) So, if you use it a lot, consider making a donation to help cover costs.

Probably no more posts this weekend, but I promise I’ll finish off the Riding a Bike saga soon (i.e., as soon as I understand it!)

I have quite an interest in game theory, which is literally what it sounds like, a study of the best way to play games, but can apply to everything from evolution to cold war politics. One of the most interesting games is the Prisoner’s Dilemma. I could talk about it for hours, but in summary (from the Wikipedia article) the basic idea is:

Two suspects are arrested by the police. The police have insufficient evidence for a conviction, and having separated them, visit each of them and offer the same deal: If you confess and your accomplice remains silent, he gets the full 10-year sentence and you go free. If he confesses and you remain silent, you get the full 10-year sentence and he goes free. If you both stay silent, all we can do is give you both 6 months for a minor charge. If you both confess, you each get 6 years.

So what should you do? For both of you together the best option is to both stay silent, but for you as an individual, you’re actually always better off confessing - if he talks, confessing will get you get 6 years instead of 10, while if he is silent, you’ll go free instead of 6 months. But if you confess, you’re risking a 6 year sentence instead of only 6 months if you’re both silent! Oh, what a dilemma! (Confusing, isn’t it?! Read the Wikipedia!)

There is in fact, no best strategy - it always depends on your opponent. More interesting is when you can repeat the game. Again, there’s no perfect strategy, but for a long time the best strategy overall has been Tit-for-tat, where you remain silent the first time, then do what ever your oponent does. Now, in a massive (computer program!) tournament, a new strategy has emerged - if you have many prisoners playing many games, some prisoners agree to take the fall so that others can triumph. And, doing this, you can beat Tit-for-tat.

Read the Wired article - it will explain this better than I can here - then go and have a game yourself (either here or here) and see how you go against the computers. Can you guess what strategy they’re playing?!

Yesterday, I made crepes (aka pancakes, depending on who you talk to, and what hemisphere you’re in.) Though I’ve been making them for years, it’s always been under my mum’s watchful eye - so any flipping has been very safely and sedately performed by a spatula! But I’m in a flat at Oxford now, with no-one to know if there’s batter on the ceiling. Or floor. Or stove. Or my head. So, I took the plunge and started flipping my pancakes! And quite successfully [Movie] too, I might add!

But it got me thinking - what’s the best way to flip a pancake? How should you throw it? How high, how hard and how much twist should it have? I thought that I might have been the first person to contemplate this fundamental problem of physics - and I would have an excuse to make lots more crepes AND put my photos on the web! But, as it turns out, physicists have already contemplated this troubling problem: from
maths and statistics to the vital equations to planning a mechanical flipper, physicists are hard at work!

Briefly, the important points are:

• Don’t try and throw the pancake straight up. A “partial vacuum” forms underneath which will hold the pancake down. Instead, slid the pan forwards and give it a flick so the pancake slides up the side and out. This also starts it rotating automatically.
• There’s got to be a perfect match between the speed you throw it up and the amount of twist, so that it makes exactly one half-revolution in the air before landing. If you want a really high flip (like me!) it’s got to turn slowly. For a low (and safer) flip, give a bit more flick of the wrist.
• Finally you have to catch it! Keep your eye on the pancake, line up the pan, and be prepared to move up or down so that it lands flat. If it’s mid twist, it tends to fold over - not desirable! It will also be moving forwards slightly, from your initial push of the pan - so don’t do this too close to a window!

I’m not going to give away my secret family crepe recipe, but Google has lots to get you started! Love to see photos of all successful flippers, and any equations you might develop too! And thanks to JP for taking the photos.

Things are getting interesting for the ethics of human cloning with Harvard university entering the debate. Harvard is planning to create cloned human embryos that will be used as a source of embryonic stem cells for therapeutic cloning.

In current embryonic stem cell applications, extra embryos from IVF treatment clinics (donated by parents) are allowed to develop until they contain a few tens of cells (a couple of days). At this point, the embryo is made entirely of stem cells, which are capable of becoming any type of cell in the body. The hope is that they can then be used to cure many diseases, such as Parkinson’s disease, heart disease, cancer - the list goes on. Although stem cells can be obtained from other sources (adults, umbilical cords), many scientists believe that embryonic stem cells hold the best chance of providing a cure.

The Harvard research is interesting, because they plan to clone cells from an adult and use them to create embryos which would provide matching stem cells to the donor. The problems with immune response to foreign cells then disappear.

As you’ve probably heard, there are many ethical issues surrounding these procedures, not least of all that an embryo is being destroyed to obtain the stem cells, which some people believe is unacceptable. Harvard must still obtain ethical clearance from the University board, and must use private funding for the research, as President Bush has forbidden federal money to be used for new stem cell or human cloning research.

Over the last two years, there has been a spike in the rate of increase of carbon dioxide in our atmosphere. In each of the last two years, the concentration has increased by over 2ppm (parts per million) compared to the fairly stable increase of about 1.5ppm. Although this has happened in the past, it has always been accompanied by the El Nino weather pattern, which wasn’t happening these past two years.

What does this mean? Maybe nothing - it could be because of the particularly hot summer in Europe and recent forest fires; it’s not a global phenomena. Or, it could signal that the Earth’s ability to absorb carbon dioxide (in oceans, forests, etc) is decreasing, which will result in further global warming. But this will further reduce the planet’s ability to handle more CO2, and so we get a “run-away greenhouse effect” where the temperatures spiral out of control.

No-one’s claiming that this is definitely what’s happening - two years of data isn’t enough to prove that - but it is once again highlighting the issues of global warming. Thankfully, with Russia agreeing to sign the Kyoto Protocol, steps are finally being taken to address the issue. While perhaps not perfect, countries ratifying the treaty agree to cut greenhouse emissions over the coming years, resulting in a 29% cut by 2010, compared to predicted levels. Notable in their absence are the United States and Australia. Shame. While I am neither a politician nor an economist, I think that we need to be willing to put the environment ahead of our economy now, or risk facing far greater losses in the future, perhaps both monetary and planetary.

A group of artists are attempting to grow a jacket out of living cells, making a seamless, leather-like garment. So far though it’s only about 5cm long, about mouse sized.

However, what’s interesting is that the team isn’t interested in the commercial applications of the technology, or even in advancing science - “…their aim is to bring to the forefront the philosophical implications of making living organisms tools for our own purposes.”

The team used a biodegradable polymer in the shape of a jacket as a base, which they coated with mouse and human bone cells to form a strong layer of skin. The idea is that the polymer disintegrates and leaves behind the completed jacket. Amazingly, people have expressed concern about the ethics of using live cells to grow jackets…but as opposed to what? Using leather from cows, wool from sheep or even cotton grown in the fields? In fact, this is part of their project - to create “…an artificial environment where semi-living entities are grown and cared for with the ultimate aim of creating a victimless utopia.” (Amazingly, the cell line they used to create the jacket was cultivated from a single mouse back in the ’70s, and there are now several tonnes of this cell around the world!)

It does raise interesting questions though - if you are against using animal products in clothes, could you still wear an “artificial” jacket, grown from cells? What if we could somehow “grow” steaks or other meat, without ever having to kill an animal - if you were vegan for ethical reasons, could you eat this? What if a single cow had to be killed to produce an unlimited supply of these cells - would you still eat the meat?

Really interesting story at Wired about engineer Amy Smith winning a MacArthur fellowship for her work in using “old” technology in brilliantly clever ways, with a particular aim of developing solutions to problems in underdeveloped parts of the world.

Her inventions making charcoal from sugar cane, for use as a cheap and clean cooking fuel, flour mills that cost a quarter of the regular price, a water testing kit for $20 instead of $1000, and more.

All this has earned her US$500,000 from the MacArthur Foundation, a no-strings, no obligations award which “is intended to encourage people of outstanding talent to pursue their own creative, intellectual, and professional inclinations.” You can’t apply for this award - you have to be selected by one of the “nominators”, who remain anonymous.

I think this sort of research is very inspring - science at its best. She’s looked at these problems, seen exactly what’s needed, and then looked for a way of solving it using simple, existing technology - for example, she fixed a water chlorinator in Honduras using parts from a toilet! She sums it up very nicely:

“Looking at things from a more basic level, you can come up with a more direct solution, and a lot of people go well, duh, that’s really obvious! But that’s what you want: people saying it should have been done that way all along. It may sound small in theory, but it in practice, it can change entire economies.”

Food for thought for anyone developing technology for the real world.

So, Part II of my bike vs unicycle physics discussion. Let’s talk about how you actually ride these, starting with a bike. If you just sit on a bike, it’s not very stable - quite quickly, the bike will tip over to the left or right. Notice you can’t fall forwards or back, because the wheels give you a large base in that direction.

However, once you start moving, it’s quite easy to balance. The common wisdom is that this is all thanks to angular momentum, a property which all spinning objects have. A fundamental law of physics is conservation of angular momentum - this says that once something is spinning, it “wants” to keep its axis pointing in the same direction. The faster it’s spinning, the more angular momentum an object has, and the stronger this principle is.

Thinking of your bike, your spinning wheels have their axis pointing left-right. Moving forwards, backwards, up or down doesn’t change this - but if you were to tip over, then the axis would have point into the ground. Angular momentum actively fights this, which helps to keep you stable! Another word for a “spinning object” which you’ve probably heard of is a gyroscope - spinning tops, Frisbees and bike wheels are all gyroscopes, as are spinning tops. Think about how conservation of angular momentum works in each of them! We even use gyroscopes in planes, so that the pilot always knows which way is up!

However, I’ve now read that this isn’t important to riding a bike. Apparently, someone built a bike with counter-gyroscopes that cancel out the angular momentum of the wheels - and yet, they were still easy to ride. So it seems as if something else is at play here! The solution is probably trail which we’ll talk more about when we come to steering. I’m not completely convinced yet, so I’ll have to read more - I’m learning something too!

Regardless, the key to riding a bike is to push off with either foot or pedal and get moving as quickly as you can - even a bit of speed greatly stabilises the bike. Once you’re moving and stable, then you can worry about pedalling to increase your speed.

A unicycle, however, is quite different. First of all, you only have one wheel, which means you can fall not only left and right, but forwards and back as well. Balancing on a stationary unicycle (called static equilibrium) is even harder than on a bike! Worse, lower speeds mean you have less angular momentum, and your weight centred quite high above the wheel means you’re able to push “harder” against the angular momentum trying to hold you up. The net result is that conservation of angular momentum definitely isn’t enough to hold you up (especially if it isn’t important even on a bike!)

What about riding? If you were to just sit on the seat and pedal, the unicycle would go flying out from under you - your seat is free to move! Instead, we must stay in dynamic equilibrium which means you start falling forwards, then pedal so that the unicycle catches up under you, fall forwards more, pedal more, and so on. This is just like walking - you lean forwards, then put your leg out to catch yourself, and repeat. There is also an element of this in riding a bicycle, but less so - and we’ll talk about it next time.

Part III follows soon, where I’ll talk about steering, wobbling and weight change!