Category Archives: Physics

The Coolest Film in the World (Still a Better Love Story Than Twilight)

IBM is pretty cool. As part of their ongoing research into data storage based on single atoms, they’ve made the world’s tiniest film. It’s called ‘A Boy and his Atom’.

It uses a handful of carbon atoms (a figurative handful of carbon atoms, obviously). A few dozen individual atoms to create a little stop-motion tale about a boy with a big grin and an atom of his very own.

The IBM film-makers used a scanning tunnelling microscope to move the atoms around and create pictures. (An IBM scientist won the Nobel Prize for Physics for inventing the STM in 1986.) It took the team of scientist film-makers two weeks of 18-hour days. Take a couple of minutes and marvel at how frickin’ awesome science is.

It’s a simple story using phenomenally complex technology. And it’s still a better love story than Twilight.

Nerd love

This post is brought to you by a crushing sense of guilt. I haven’t blogged here for ages. AGES. I just haven’t made the time (note the honesty there: I could have had the time).

I’ll slip in the news that I have dropped out of my physics course. It was just too much to cope with at the moment. I don’t feel guilty; I feel like a weight has been lifted from my shoulders. I’ll pick it up again when I’m in a position to do the course, and myself, justice.

Anyway: it’s Easter, and it’s April Fools’ Day, so here’s a little something from one nerd to lovers everywhere. If you’re going to propose, do it in style. Or memorably. Or nerdily.

How nerds propose: an academic paper.

Will you consent to an indefinite two-body interaction?

Lightning has an electromagnetic personality

In the late 1700s, Charles Augustin Coulomb put the snap, crackle and pop from a number of perilous experiments together and deduced the form of the electrostatic force law. Here’s what he found:

  1. You can’t tell just by looking at an object whether or not it carries a charge. Unless you’re an X-Man. Possibly.
  2. There are only two types of charge: positive and negative. Opposites attract, as the old cliché goes. And an object with equal amounts of each is electrically neutral, like Switzerland.
  3. All normal matter contains electric charge (except Findus lasagnes, which are not yet understood by science).Electrons may be transferred from one object to another.
  4. In an isolated system, the total electric charge is always conserved. So when you rub a balloon on a cat, no charge is created – electrons are simply redistributed between the cat and the balloon (and anger is created in the cat. Cats are often not subject to the usual laws of physics. Mine can teleport). Charge has its very own law of conservation.
  5. Because of the attraction between unlike charges, any item with a deficit of electrons (which has, therefore, a positive charge) will attract negatively charged items. But that’s not all: it will also pull in any electrons that happen to be hanging around. That’s how electric currents work, in the very simplest terms. Put a negative thing next to a positive thing, and electrons will flow from one to the other until they’re sharing them equally.

Fun facts about electric charge

  1. A small plastic troll doll with purple hair. Looks like it's been introduced to a Van der Graaf generator.

    Me. On a Monday.

    If you super-dry your hair then give it a vigorous brushing, you can make it stand on end. I often don’t need to put this much effort in; my barnet’s natural state appears to be one resembling those little trolls. 

  2. You can stick balloons to the ceiling using electrons, thus defying the laws of gravity. This is an interesting demonstration of the difference in strength between the electrostatic force and the gravitational force. Relatively speaking, the electrostatic force is MUCH stronger. Mind-bogglingly so. (Although you can’t really compare them, because they are fundamentally different things with arbitrary units of measurement.
  3. If you’re wearing nylon clothes, and you take them off in a dark room, you can sometimes see sparks as the separation of the clothing from your skin causes the air around you to undergo electrical breakdown. You can dismantle the air, like an X-Man. Possibly.
  4. Electrostatic charges are responsible for lightning. (More below.)

One of my favourite things is finding out that an everyday (but brilliant) phenomenon is still not fully understood by our biggest brains. We really don’t understand how lightning works! Partly because experiments are bloody dangerous…

A scientist named Georg Wilhelm Richmann, a German physicist living in Russia, was killed during a lightning experiment in 1753. He has the dubious honour of being the first person killed during an experiment involving electricity.

He was electrocuted in St Petersburg while “trying to quantify the response of an insulated rod to a nearby storm”. Any excuse to duck out of a meeting, even back then: he dashed off on hearing the news of a thunderstorm, taking his engraver with him to record the event for posterity.

During the experiment, and somewhat predictably (with the benefit of hindsight), he was struck by lightning. (It’s said that it was ball lightning, a very rare phenomenon that wasn’t believed to exist until the 1960s.)

The explosion that followed blew up his shoes, singed his clothes and knocked him dead. That wasn’t the end of his scientific exploits, however; his body was dissected to find out what effect his terminal experiment had on his organs.

We don’t understand lightning

Lightning is probably the most dramatic and well-known natural phenomenon resulting from electrical charge. But how does it work? Well, here’s what we know:

  • On humid days, rising air currents carry water vapour up into the atmosphere.
  • This occurs in giant clouds – they’re around 10km thick.
  • The water droplets cool as they rise, then freeze to form hailstones. Hailstones are required for lightning to occur.
  • The hailstones grow as more water condenses on them, then begin to fall under gravity when they become obese.
  • As they fall, they tend to melt and emerge from the cloud as heavy rain.
  • Lightning flashes develop near the base of a cloud, and are caused by the separation of positive and negative charges within the cloud.
  • The electrical activity occurs at an altitude where the temperature is between 0°C and -10°C – the only temperature range in which both hailstones and supercooled water drops can exist simultaneously.

Beyond these facts, we’re not really sure of anything!

We all know what lightning looks like, but this video shows a whole plethora of beautiful phenomena set to the strains of Robert Miles epic tune ‘Children’. One of the soundtracks to my messy youth.

Theorising about lightning

Most of the theories about the origins of lightning are based on a transfer of charge between the rising water drops and the falling hailstones. This leaves the water drops with a net positive charge and the hailstones with a net negative charge.

With the water drops pulled to the top of the cloud by rising air currents, and the negatively charged hailstones falling under gravity, the result is a net excess positive charge near the top of the cloud and a net negative charge near the bottom.

The tops of clouds are happy. The bottoms are angry.

Diagram illustrating the charge distribution in a thundercloud.

This process increases until the electrostatic charges are so large that one of two things (may) happen:

  1. The vapour in the cloud undergoes electrical breakdown, allowing the electrons to flow up through the cloud in a giant spark of lightning – a ‘cloud flash’.
  2. The air beneath the cloud suffers electrical breakdown and the negative charge at the bottom flows to the positively charged ground as forked lightning.

As I said, though, the charging mechanism is not really understood. The middle of a thundercloud is a bit of a hairy place to be, so there are not many experiments documented. I quite fancy making some kind of protective bubble and mooching into a cloud. If anybody would like to fund this hare-brained scheme, do drop me a line. You could be in line to share a Nobel Prize, you never know…

Our Slow-Burning Star

IMG_0814Ever wondered why the Sun hasn’t burned out yet? Or why, exactly, it will still be going in several million years?

‘Well, it’s very big!’ I hear you say. ‘There’s lots of fuel in there.’ Yes; yes, it is very big, and there is a lot of fuel. But that’s not why it’s such a long-term heat and light source. It is a little more complicated than that…

Here’s an interesting fact: kilogram for kilogram, the Sun puts out less energy than a human body. It is far less efficient than we are at generating power.

On the face of it, this is a little surprising – it’s an enormous flaming ball of gas that we couldn’t get anywhere near without disappearing in a puff of carbon. So how can it be so inefficient?

The answer lies in the fact that it is, indeed, a great big ball of gas and it behaves in a very similar way to gases on Earth. It turns out that gases are rather interesting and the way they behave under different conditions is predictable.

The Maxwell-Boltzmann curve

The distributions of speed and translational (movement) energy of the molecules in a gas are very similar if a gas is in equilibrium. The more molecules the gas contains, the fewer fluctuations in speed and energy distribution.

Essentially, this means that a certain percentage of gas molecules will tend to have a certain speed or energy level. This is best demonstrated using a Maxwell-Boltzmann graph:

A graph showing the Maxwell-Boltzmann curve of molecular speed distribution, with the most probably speed indicated.

The Maxwell-Boltzmann curve of molecular speed distribution

This graph shows that there is a most-likely speed for any given gas molecule to have (and a similar curve exists for molecular translational energy). As long as the temperature of the gas is constant, the fraction of molecules with the most probable speed remains around the same (as does the fraction of molecules with any other speed).

(Note that molecules with a given speed may not be the same; their individual speeds keep changing as a result of collisions with other molecules, or the gas container.)

The graph has a long tail at higher speeds and energies: the likelihood of finding a molecule with a certain speed and energy decreases as speeds and energy levels increase. It’s the same for protons in the Sun.

This is the reason for the Sun’s longevity: the chance of two protons coming together in nuclear fusion is tiny. It has been estimated that it takes one proton five billion years to fuse with another proton. Most of the time, protons zip around in the Sun at relatively low speeds and energies, bouncing off one another and carrying on their merry way.

They are to be found in the ‘lumpy’ part of the distribution curve; the area with the ‘most likely’ speeds and energies. It is only when a proton (or molecule) falls into the tail end of the curve that it approaches the speed and energy required to undergo fusion.

A graph showing the energy distribution curve of protons in the Sun, with the area where fusion will occur highlighted in purple.

The tail-end of the energy curve, where fusion will happen.

Most of the Sun is too cold for fusion. When those very few protons in the tail end of the distribution curve do come together in fusion, they release large amounts of stored energy.

It is, therefore, extremely unlikely that fusion will occur in the Sun. However, it’s so massive that its total energy output is enormous so it is pretty hot. And bright. If the distribution patterns of speed and energy were different, the Sun could have burned out millennia ago, or may never have got very hot at all.

Gases are predictable

The speed distribution of a gas depends on the mass of the molecule, but the translational energy distribution is the same for all gases at the same temperature.

In other words, the larger the molecules’ mass, the slower their speed; so the speed distribution will be affected by molecule size. However, the molecules’ mass has no effect on the energy distribution – it’s the same for all gases at a fixed temperature.

  • The speed and energy of a gas’s molecules increase as the temperature increases, as long as the volume is fixed.
  • The molecules’ energy is unaffected by a change in speed at a fixed temperature and volume.
  • The speed and energy are unaffected by an increase in volume, at a fixed temperature.

These properties have been extremely useful in the development of technology – and led to the invention of a simple but quite marvellous fire-starting device: the fire piston.

Because compressing gases leads to an increase in temperature, if you do it quickly enough you can ignite flammable material without any need for sparks or traditional fuel. An old-fashioned fire piston is still useful today for campers, climbers and other such adventurers. It’s small and easy to use: take a long, thin cylinder, a rod or piston, and place some flammable material in the bottom of the cylinder. Plunge the piston down rapidly, and watch the material ignite. This video shows you how to make one, which I will do at some point:

Science in action. It’s marvellous!

Why I love science

Or, at least, this is one of the reasons I love science…

Take a look at this article in Nature. It’s interesting, yes – especially if you understand anything of quantum gases. But it’s the comments that made me laugh!

The article also underlines our everyday misunderstanding of and misuse of terms such as ‘temperature’ and ‘heat’.

Dive in!

Nature article

Science also invites respectful, light-hearted banter. Compare this to the trolling and abuse you often see in the comments sections of blogs and YouTube…

May all the forces be with you!

The title of this blog is taken from Book 3: Predicting Motion from my S207: The Physical World OU course book. It made me chuckle.

At the moment, I’m studying forces and pressure, and the line above was in reference to the fact that we don’t implode under the weight of the atmosphere. Normal atmospheric pressure is about 1.013 x 105 Pa, which exerts a force equal in magnitude to the combined weight of 163 people, each of mass 63.5 kg, on a patch of Earth one metre square. That is a LOT of weight.

How are we not crushed? Well, the pressure inside our bodies is approximately equal to the pressure outside, so all the forces just about balance. Which means we are in perfect balance with our normal environments. Simple!

Fictitious forces

So, forces. Everyone knows what a force is, right? The equation is F = ma (force = mass x acceleration). There is frictional force, centripetal force, weight, and the linear restoring force… but what isn’t there?

Fictitious forces are not real forces at all; they are associated with real phenomena that arise when we use non-inertial frames of reference (i.e. frames of reference that move around). Newton’s laws of motion can only be applied in inertial frames of reference. They start to collapse in the face of excitement…

Gravity: No, gravity is not a force. Gravity is a downward acceleration that is, on Earth at least, approximately equal to 9.81 m s-2. That means that any object falling under gravity (assuming that there is no friction or air resistance) falls at a speed which increases at the rate of 9.81 metres per second, every second.

Gravity does, however, give rise to a force: weight. Our everyday use of the word ‘weight’ is not, technically, correct. We use it to mean ‘mass’, which is constant wherever you may be. Weight is a force arising from gravity, described by the equation W = mg (weight = mass x gravity) and it varies depending upon its environment. For example, you weigh more here than you would on the Moon.

Under gravity, objects exert a force (weight) upon the rigid surface on which they rest. The rigid surface exerts a force right back at it, called the normal reaction force. These two forces balance, meaning that the object stays where it’s put, unless it is acted upon by an unbalanced force, such as a good hard kick.

The Coriolis force: This is a weather phenomenon that is actually pretty cool. In the Northern Hemisphere, moving air masses tend to wander off to the right, as if they were being pushed there by a force.

Arising from the Earth’s rotation, this result is not due to an unseen force at all, but is due to the fact that the motion of the air masses is being observed from the non-inertial frame of the spinning Earth.

The air masses are moving in a straight line, as all things are wont to do under their own steam; it is the rotation of the Earth that makes the air appear to veer off to the right in the North. The effect is real enough; the force is an illusion.

Centrifugal force: Everyone who has ever travelled in a fast-moving car, or been on a roller coaster, knows exactly what centrifugal force is. It pushes you out to the side when you go round a sharp bend at speed.

Except it doesn’t. From the frame of reference of the car’s interior, you’re pushed by an outwardly directed ‘centrifugal force’, but this, too, is an illusion. Think outside the box. Or outside the car, if you like.

Unless acted upon by an unbalanced force, all objects in motion will tend to travel in a straight line – even you. Within a car, you will tend to travel in a straight line, regardless of what the car is doing. It is only when your forward motion connects with the side of the car as it’s making the turn that your motion deviates from the straight and narrow. So although it feels as though an unseen force is throwing you to one side, it isn’t. In fact, you are travelling in a straight line until you are no longer able to because the car door is in the way.

Acceleration in a straight line: Another car example. Cars are great for describing and examining forces in physics. When a car accelerates, you get pressed back into the seat by the force of… what? Well, nothing. In an inertial frame of reference, e.g. the one attached to the road, there is no physical force moving you backwards.

The non-inertial reference frame attached to the moving car does have a backward fictitious force though. In fact, the real force is the forward force produced by the car’s engine. When the car accelerates, you carry on moving at the pace you were moving at before, until the solid seat requires you to move along with it.

Put your mind outside the car and observe from there: you’re not subject to any forces that the car is not subject to.

Treating the fictitious forces as real forces within their non-inertial frames of reference allows us to apply Newton’s laws them, which can be kind of useful. It’s important though to remember that they are not real forces. They are nature’s illusions.

S207: the story so far

So far, S207 is fabulous, but very challenging. The maths is extremely tricky for those without a background in maths, so I’m finding it hard going. Challenging is good: it makes it all the more rewarding when I realise I understand something fully. TMA01 netted me 78 per cent, which I’m pretty happy with – plus my tutor’s comments were really helpful. Bring on TMA02!

Things I am struggling with so far:

  • Simple harmonic motion: not so simple
  • Interpreting graphs. I don’t know why; it’s a mental stumbling block

Everything else, I’m taking my time with. The more I do, the more it makes sense. And every now and then I come back to something I was struggling with, and suddenly it makes perfect sense. Which is nice…

The Higgs Boson: explained!

For those not clear on the Higgs boson (what it is, what it’s for, and why), it’s explained here. Sort of. A little.

(Thanks to my S207 forum for that one!)