Month: March 2015

Categories
Coffee review Observations Science history

A ‘brief’ encounter at Coffee Affair

Coffee Affair, Queens Road Station
The exterior of Coffee Affair, yes it really is inside the station

It was a few weeks ago now that I dropped into Coffee Affair on a Saturday afternoon and met Michael (who runs Coffee Affair along with ‘Mags’). What can I say? This place is worth visiting for so many reasons. Firstly of course there is the coffee, so much care and attention to detail was taken when I ordered a pour over Burundi coffee from Round Hill Roastery. I was warned that my coffee would take some time to prepare before the filter was carefully rinsed and the coffee weighed and ground. The final coffee having been made with such attention that I started to understand why they had chosen the name ‘coffee affair’. It is clear that coffee is a passion.

Parquet floor at Coffee Affair
The floor at Coffee Affair.

Then there is the knowledge that Michael brings to the coffee and is happy to share. Thoughts about the best temperature to drink the coffee for example, or details about different brew methods (there is a lovely array of coffee brewing equipment on the wall of the cafe). One thing that really appealed to me though was the place. There are only a couple of tables and a bar but this emphasises the space that Coffee Affair inhabits: A preserved old ticket office. There are windows looking into the station with bars on them through which the tickets used to be sold. There is the oak table that has had years of ticket sellers leaning on it, presumably with a lamp next to their counter as it would have been a lot darker when it was used as a ticket office. Then there is the flooring, original parquet flooring that dates from the time that the station was built.

If you take a seat towards the back of Coffee Affair and look at the floor you can see where the floor has worn down just that little bit as ticket sellers from years ago shuffled at their counters while selling tickets. Like the toe of St Peter, the floor has been worn away by the number of people in contact with it over the years. Between the counters you can see where someone has tried to polish the parquet to minimise this ‘dip’ but has instead managed to produce lines in a slightly more polished floor. Thinking about the wear of the floor reminded me of Charles Darwin’s musings about the erosion of the Weald in the South East of England.

Goudhurst area
How long does it take for such landscapes to form?

In the first edition of Darwin’s book “On the Origin of Species” (1859), Darwin included an estimate for the age of the Weald of Kent, the area between the chalk hills of the North and South Downs. Based on his observations of coastal erosion, Darwin calculated that the Weald must have been at least 300 million years old. This was perfectly long enough for the gradual evolutionary steps of natural selection to have occurred. As Darwin said “What an infinite number of generations, which the mind cannot grasp, must have succeeded each other in the long roll of years!”* Looking at the floor at the Coffee Affair, you can get a similar idea as to the number of generations that have stood at the ticket windows.

Darwin’s estimate of the age of the Weald led him into an argument with William Thomson (Lord Kelvin) about the age of the Earth (which you can read more about here). It was Kelvin’s argument about the age of the Earth that Darwin considered “the single most intractable point levelled against his theory during his lifetime”†. The argument was eventually settled in Darwin’s favour, once new physics had been discovered, but only after both Kelvin and Darwin had died. So I’ll leave Darwin the last words for today’s Daily Grind, relevant too for those who have the opportunity to study the floor at Coffee Affair: “He who most closely studies the action of the sea on our shores, will, I believe, be most deeply impressed with the slowness with which rocky coasts are worn away”.*

 

Coffee Affair is in the old ticket office at Queenstown Road Station, Battersea,

* Quotes from “On the origin of species”, Charles Darwin (Oxford World Classic’s edition, 2008)

†Quote taken from “Charles Darwin, The Power of Place”, Janet Browne, Princeton University Press, 2002

Categories
Coffee cup science Observations Science history

Perpetual motion in a coffee cup

V60 from Leyas
Could your coffee be used to power a perpetual motion machine?

There can be no such thing as a perpetual motion machine right? Yet less than two hundred years ago it seemed possible that there could be. Not just that, the source of this perpetual motion machine was in your coffee cup. How would you explain Brownian motion?

Brownian motion is the random movement of small bits of dust or coffee/tea particles on the surface of your brew. To see it, you may have to use a microscope though you should take care not to confuse Brownian motion with motion caused by convection currents. There will be Brownian movement even a long time after the coffee has got cold. What causes this continuous movement? When he observed it for the first time in 1827, Robert Brown (1773-1858) had thought it was to do with a ‘life force’. He had been observing pollen suspended in water and noticed that the pollen kept moving under his microscope lens. In 1827, this was a very reasonable explanation, after all, weren’t several people looking for a motion, a force, that gave life?

Sphinx, Brownian motion
Brown used some dust from the Sphinx (shown here with the Great Pyramid) to show that ‘Brownian’ motion could occur in inorganic materials. Postcard image © Trustees of the British Museum

So, he checked if he saw the effect in pollen that was one hundred years old (he did) and then in truly inorganic matter, he looked at the dust from a fragment of the Sphinx. Again he saw the dust fragment move in the water. He had therefore shown that it was not associated with a life force but was something that happened for every small particle suspended in a liquid. What was driving it?

Without knowing what caused it, some people in the nineteenth century had already suggested a device to exploit it, using tiny levers to carry the energy from this continuous motion into devices. Others insisted on finding out what was causing the motion but it was here that the physics of the day hit a philosophical problem. It was proposed that molecules in the water could be hitting the dust on the surface and moving the dust in seemingly random directions. And yet there is a problem with this explanation. At that time there was no way of seeing or measuring molecules. How could physics postulate a theory – or suggest a reality – that could not be tested?

Nasa, Norway, coastline, fratal
How long is a section of coastline? Coastlines can be described as fractal like. Mathematics that grew out of studying random walks and Brownian motion. Image credit NASA Visible Earth/Jeff Schmaltz

An answer came one hundred years ago in a paper published by Albert Einstein (1879-1955) in 1905. In it he made some mathematical predictions that, for the first time, allowed the theory (that it was molecules causing Brownian motion) to be tested by experiment. Jean Perrin (1870-1942) of the Sorbonne, Paris, was the experimentalist who, by careful observation of droplets of water containing a pigment used by water colour artists, provided evidence for Einstein’s theory of Brownian motion. The experiment was so important that Perrin later wrote “.. the molecular kinetic theory of Brownian movement has been verified to such a point in all its consequences that, whatever prepossession may exist against Atomism, it becomes difficult to reject the theory.”

The consequences for our world have been profound. The mathematics that describes Brownian motion is that which we use as the basis to predict the movements of the stock exchange. Extensions of the mathematics have been used to develop new areas of mathematics such as fractals. Even art has grasped the theory of Brownian motion, the Anthony Gormley sculpture “Quantum Cloud” is based on mathematics describing Brownian motion. Everywhere you look there are phenomena described by the movements in your coffee cup. What we have yet to do is find that perpetual motion machine.

Categories
Coffee review Home experiments Observations

Sugar castles at Iris and June, Victoria

Iris and June, Victoria, coffee in Victoria
The exterior of Iris and June

This post has been a long time coming. Over the past few months I’ve been popping into Iris&June to get take away coffee now and then and have got quite fond of the friendly service and good coffee. What I have not really had the opportunity to do (until recently) was sit and enjoy a coffee inside. Fortunately that’s now changed and I can add Iris&June to the Daily Grind.

So, how is I+J? Well, it is a 5 minute walk from Victoria train station and a welcome break for good coffee. They serve Ozone based espresso, with a brew bar which features guest roasts (also from Ozone) made with the V60 or Aeropress. There are a good looking selection of cakes on offer, though sadly, on the day that I could sit inside with my drink, they all had nuts in them. Hopefully another time.

Sugar jar, I&J, I+J
A jar of sugar at Iris and June

I took a seat on the cushioned bench near the wall and started to look at what was going on. It is the sort of place that is very good for people watching. My eye though was drawn to what was on my table: a jar of sugar. It is not that I take sugar in my coffee, it is that I was reminded of a tutorial I once had as a student. I cannot remember the exact conversation but it concerned piles of sand. My tutor (a theoretical physicist) had said something along the lines “Ah yes, well, of course, everyone knew the maximum angle that a pile of sand could make before it became unstable and then how it started to collapse…. Until of course someone measured it.” [laughed] “We’d got it entirely wrong.”

This ability to laugh at what we do not know, (or what we assume we do know and then measure it and find out that in fact we do not)  is one of the pleasures of physics. We are trying to understand the world we live in, we have not yet got there. Sometimes it is the smallest things that are not yet understood, such as how and why (dry) sand forms avalanches as it is piled up. Yet these small things can turn out to have big consequences (as was also the case for the understanding of coffee stains). In this case, the experiment had tested the way that a pile of sand collapsed in response to different shaped grains of ‘sand’. It had relevance then (and continues to have relevance now) not only in terms of granular dynamics: how do we predict landslides/avalanches? But also in terms of crucial theoretical models about how these processes behave. Theoretical models that are applied to systems as diverse as knowing how electrical devices (resistors) work to understanding the noise on the luminosity of stars. Realising that we were wrong enabled us to probe the question more deeply and thereby to understand it more.

There are similarities between sugar and sand, but also key differences. Although it was tempting to start building sugar castles in the sugar jars on the tables at Iris and June, I was aware of the impression that I may have made to those who go to I+J to people watch (see above). I will therefore leave it as a home experiment. How steep a sugar castle do you think you can make? And how steep can you in fact make it, what is the role of water in building sand castles?

Please leave any reports of experimental results for how steep you can make a pile of sugar in the comments section below and feel free to send me your sugar-castle pictures.

Iris and June is at No 1 Howick Place, SW1P 1WG

Categories
Home experiments

The hot chocolate effect

hot chocolate effect, Raphas
A ready prepared hot chocolate

This is an effect that reveals how sound travels in liquids. It enables us to understand the milk steaming process involved in making lattes and yet, it can be studied in your kitchen. It has an alternative name, “The instant coffee effect”, but we won’t mention that on this website any further. To study it you will need,

1) a mug (cylindrical is preferable),
2) some hot chocolate powder (no, instant coffee really will not do even if it does work)
3) a teaspoon
4) a wooden chopstick (optional, you can use your knuckle)

Make the hot chocolate as you usually would and stir. Then, remove the spoon and repeatedly tap on the bottom of the mug with the wooden chopstick (you could instead use your knuckle). Over the course of about a minute, you will hear the note made by the chopstick rise (not having a musical ear, I will have to trust that this can be by as much as three octaves).

resonator, mouth organ
The length of the pipes in this mouth organ determine the note heard. Photo © The Trustees of the British Museum

What is happening? Well, just like an organ pipe, the hot chocolate mug acts as a resonator. As the bottom surface of the hot chocolate is fixed in the mug and the top surface is open to the air, the lowest frequency of sound wave that the hot chocolate resonator sustains is a quarter wavelength. The note that you hear depends not just on the wavelength, but also on the speed of sound in the hot chocolate, and it is this last bit that is changing. When you put in the water and stir, you introduce air bubbles into the drink. With time (and with tapping the bottom surface), the air bubbles leave the hot chocolate. The speed of sound in a hot chocolate/air bubble mixture is lower than the speed of sound in hot chocolate without air bubbles. Consequently, the frequency of the note you hear is higher in the hot chocolate without bubbles than in the former case.

Let’s use this to make a prediction about what happens when a barista steams milk ready for a latte. At first, the steam wand introduces air and bubbles into the mixture but it is not yet warming the milk considerably. From above, we expect that the speed of sound will decrease as the bubbles are introduced. This will have the effect of making the ‘note’ that you hear on steaming the milk, lower. At the same time the resonator size is increasing (as the new bubbles push the liquid up the sides of the pitcher). This too will act to decrease the note that is heard as you steam (though the froth will also act to damp the vibration, we’ll neglect this effect for the first approximation). At a certain point, the steam wand will start to heat the milk. The speed of sound increases with the temperature of the milk and so the note will get higher as the milk gets warmer.

So this is my prediction, musically inclined baristas can tell me if there is any truth in this:

1) On initially putting the steam wand into the cold milk, the tone of the note heard as the milk is steamed, will decrease.
2) This decrease will continue for some time until the milk starts to get warm when the note increases again.
3) Towards the end of the process, the note heard on steaming the milk will continue to increase until you stop frothing.
4) It should be possible, by listening to the milk being steamed, to know when the milk is ready for your latte just by listening to it (if you are experienced and always use similar amounts of milk per latte drink).

So, let me know if this is right and, if it is wrong, why not let me know what you think is happening instead. I’d be interested to know your insights into the hot chocolate effect in a milk pitcher.