surfaces – Bean Thinking

coffee Clapham common — Weather for Wimbledon? It was raining when we tried Brickwood in Clapham

It was raining heavily as we met friends for coffee at Brickwood, near Clapham Common, a few weeks back. Inside it was fairly crowded so we were shown to a cosy little area downstairs where we found a table. The staff were all friendly and with coffee roasted by Caravan, it was easy to sit and enjoy a great Americano while waiting for the others to arrive. Sadly, all of the cakes on the menu contained nuts (with the exception of scones). This was a shame because it was otherwise an interesting place to sit and observe the surroundings and it would have been nice to have been able to give it a ‘tick’ in the cafes with good nut knowledge box*. Still, the coffee was very good and there was plenty to observe, even in the basement.

Glancing around the room, the first thing that struck me was a white board on the wall. Taken together with the artificial lighting (necessitated by the area being in the basement), this was highly reminiscent of the maths ‘common room’ at work. A further mathematical connection comes from the fact that the grandfather of John Venn (of the Venn diagram) lived nearby. A prominent local clergyman, Venn St, just around the corner from Brickwood, is named after him. Still, that is quite a digression. There were also interesting bits of physics and science to notice in the café itself.

the 'carpet' of the floor at Brickwood — Grass or concrete? What factors control the bounce of a tennis ball.

Downstairs, the floor was covered in what appeared to be an artificial grass. This gave the whole experience of having a coffee here a bit of a surreal twist. Just as happens with real grass, a path was visible on the ‘grass’ where people had walked, something that can be used when rambling in the country to help you find your way around (when GPS or map temporarily fail you). The book “The Walker’s Guide to Outdoor Clues and Signs” gives many such details about how to navigate in the country without a map (including how to tell from trees which way is North).

However, as we are now in the second week of the Wimbledon Tennis tournament, this cafe-physics review is going to have a tennis slant instead. We could think about how different it would be were we to drop a tennis ball onto the ‘grass’ downstairs, or (what I remember to be) the wooden floor upstairs. Tennis started off as an indoor sport, played on courtyards in stately homes and monasteries. ‘Lawn tennis’, or what we now recognise as just ‘tennis’, developed in the nineteenth century and was played on grass. Thinking about how a tennis ball would bounce on the floor in the basement or upstairs in Brickwood is therefore somehow reminiscent of the history of the sport.

whiteboard, Brickwood, Clapham — Like being in the maths common room but with better coffee and flowers

Tennis balls are designed to bounce 53-58 ” (134.6-147.3 cm) when dropped onto a concrete floor from a height of 100″ (254 cm). Other surfaces have different elasticity and/or friction. The behaviour of the ball will be quite different therefore when it bounces on different surfaces, affecting the speed (and therefore height) and even angle of the bounce (for more info on the physics click here). The different characteristics of the surfaces mean that different types of play are required to succeed on the court. To be successful across all courts (from the clay of Roland Garros to the Decoturf of the US Open and the grass of Wimbledon) requires a tennis player who can adopt many different playing styles. Would it help a tennis player to have a training in physics and an understanding of the details of aerodynamics, spin and friction that are involved as the ball whizzes through the air? Probably not. But for us mere observers who prefer eating the strawberries and cream and savouring great coffees while discussing the game, a bit of physics may perhaps add to our enjoyment.

Brickwood (Clapham) is at 16 Clapham Common South Side, SW4 7AB

*to be fair, Brickwood did have “good nut knowledge”, they knew all their cakes contained nuts. Perhaps the tag needs revising to be “nut-allergy-friendly”.

It’s a kind of magic at Kaffeine

It’s nearly 7 years since Kaffeine first opened its doors on Great Titchfield St, but Kaffeine on Eastcastle Street is a new addition having opened just over a year ago. We visited the younger Kaffeine a couple of weekends ago when looking for a coffee in the Oxford St area. Along with an iced coffee, an Americano and a long black, we had a raspberry/cashew slice and a slice of banana bread. It was a relief to find that Kaffeine had a good nut policy so I could confidently enjoy my banana bread, knowing it was nut-free, while a friend devoured the cashew containing slice. The staff were attentive and friendly and there was plenty of space inside to sit and chat while taking in the surroundings. In this regard, it was nice to see this same point being made on Kaffeine’s own website where it says that you can “…sit at the high stools at the massive sun filled front windows and watch the world go by”. With the accompanying coffee, what more could you want? The coffee was, of course, very good (beans from Square Mile), and it was great to see that part of the philosophy behind Kaffeine is to take “the art and science and practice of making espresso coffee to a whole new level”. It’s always a pleasure to see those three distinct, but essential, elements combined. I do however remain unconvinced that many could tell the difference (in a blind taste test) between an Americano and a long black.

wood and slate with glass, Kaffeine — The table top at Kaffeine, Eastcastle St.

Complimentary mint-infused water was on offer at the back of the cafe and, although this made the Daily Grind last week, there was just too much to notice at Kaffeine to make this the subject of the cafe-physics review. Indeed, from the perspective of anyone who wants to slow down and notice things in a café, Kaffeine is brilliant. This cafe-physics review could have been about so many different things. There were the weights holding the door open in a pulley system. The trademark neon sign. The compact-ness of the cashew/raspberry slice or the reflectivity of the copper on the side of the counter. I was in cafe-physics review heaven! So many different mental alleyways to run down and explore as the different bits of physics came into view. From pulleys to Archimedes, cakes to ceramics science, copper to atoms or to the odd puzzle about the colour of gold, all these will have to wait for another time. This time, what struck me was not what could be seen but what could be felt.

Far from going into a subjective piece about the ambience of the cafe, I mean this statement far more literally. The table, with the wooden grain, felt rough. In the middle of the table, a piece of slate had a surface that was more smooth and then, on the walls behind us, highly glazed tiles were very smooth indeed. What do we mean by rough or smooth, how rough is rough, how smooth is smooth and what has it to do with the “magic mirrors” of Japan?

reflective tiles but not really flat yet — Smooth tiled wall at Kaffeine

The wooden bit of the table for instance has a surface that undulates with a height of the order of about a millimetre. The slate is far smoother but the surface would still be rough, probably on a length scale tens to hundred microns or so (about the size of espresso to medium grind coffee). The tiles are a lot smoother than both the wood or the slate but they are still not so smooth that they could be considered flat on an atomic scale. To be flat on an atomic scale, the surface would have to have a height variation 100 000 times smaller than the smallest particles in an espresso grind*. While some crystals can, naturally, have ‘faces’ that are this smooth, the semiconductor industry needs to be able to achieve this level of flatness routinely to provide the electronics for your smart phones, computers and even perhaps the electronic scales that are used to help you make your coffee.

copper mirror Kaffeine Eastcastle St — The mirror-like copper clad counter.

In ordinary life however, perhaps we think that a smooth surface is like that of a mirror. So it is worth taking a look at an odd type of mirror for which very small variations on the surface cause a very strange effect: the “Magic mirrors” of the far East. Typically made of bronze, these mirrors have been manufactured for nearly 2000 years. On the back surface of the mirror is an artwork (perhaps signs of the zodiac or other religious symbols) which is in relief. The front of the mirror meanwhile is highly polished but slightly convex. Looking directly at the front surface of the mirror, there is no visible sign of the image on the back. Maybe you don’t find this surprising, the mirror is solid bronze after all and we can’t see through solid metal. However, if you were to take a step back, shine light on the front of the mirror and look at the reflection of the mirror projected onto the wall, the image at the back can clearly be seen, there in the reflection (you can see photos of this effect here).

Initially this phenomenon was dismissed as ‘trickery’ but subsequent, careful, study showed that small deviations from perfect curvature on the reflecting surface were enough to cause the effect. Although the mirrors were cast and then polished, nonetheless, stresses and strains from the pattern on the back had propagated through the atomic structure that forms the metal and resulted in tiny, invisible to the eye, changes on the front surface of the mirror. Sometimes it does appear that looking at things in a different light can really change our impression of what something is.

Kaffeine can be found at 15 Eastcastle St. W1T 3AY

* Scaling to coffee grind size approximate but based on measurement of grind size reported here.