We delayed our visit to Under the Willow Tree by a day because we noticed that the cafe was closed on Monday afternoons owing to “Sing and sign” sessions for the local community. What a brilliant idea and the sort of community engagement that makes a neighbourhood cafe particularly special. Definitely a cafe to visit.
Coffee is by Grumpy Mule while the tea is by Ero’s. There is a good selection of pastries on the counter and food for brunch/lunch on the menu. The only problem was that there was no sign on the frontage of the cafe to tell us that we’d arrived, we guessed based on the postcode and the fact that this was the only place serving this sort of coffee in the area.
The cafe is definitely child-friendly. With a children’s play area at the back and toys on the shelf by the water, there is plenty for kids to do while their parents enjoy some time with a coffee. Although there are also tables away from the play area if you wanted a coffee away from the kids. A table towards the back of the cafe is suspended by rope perhaps making you think of swings, or tree houses, while the rest of the cafe is fairly minimalist, focussing you on the coffee and the play.
It is no bad thing to focus on play and indeed, it could offer a first physics connection, or at least materials science, with this cafe, in the form of the English Willow needed to make cricket bats for Test cricket. The fibres within the wood provide the toughness needed to prevent the wood from splintering as the ball hits the blade.
But keeping with the Willow tree, the remarkable thing about it is how it bends down to the water’s edge, providing shade and shelter for all manner of wildlife. There is another type of deciduous tree in a London park that hangs across a footpath, lazing in a manner similar to that of the willow at the water’s edge. And although it is perfectly possible to walk underneath it on part of the path, I find it perhaps more respectful to bow to the tree as I walk underneath. Walking the path at different times of the year, it is noticeable that the amount I need to bow increases as winter moves into spring and summer. The weight of the leaves pulls on the branches pulling them down.
As the tree has horizontal branches hanging over the path, it is not a simple case of Hooke’s law (where the amount the tree stretches down is directly proportional to the gravitational force of the leaves acting on the branches). But nonetheless, it does give you an indication of the collective mass of the leaves.
The fact that the tree dips down towards the path when it has leaves and moves up away from the path each winter, implies that the tree branches are acting within the elastic limit. That is, that the response of the branch to a load is still reversible. If the stress becomes too much, the extension of the tree will become plastic rather than elastic and the branches would not return to their original position. The elastic limit will vary from wood type to wood type and with different materials. Sometimes we would want elasticity and so we’ll choose one wood type, sometimes rigidity and so another. One reason that willow is a good wood for cricket bats is also this elasticity: the elasticity of the wood as the ball hits it being determined by small pockets of air in the bat.
There is a similar balance that may occur in your coffee cup if you enjoy a cappuccino. The difference between a pourable foam and one that stands ‘peak like’ on the cup. The ability of the barista to pour and draw the latte art requires a foam that is fairly stiff but still pourable. This is quantified by measurement of the “yield stress” of the froth. The yield stress is the minimum shear stress needed for a liquid or foam to start to flow. So to make latte art, you would need a foam that is stiff enough to hold the design, that is, it has lots of little bubbles that make the foam more firm. But at the same time that the foam is not so stiff that it does not pour (so you need to ensure that you have a lot of liquid milk content within the foam). The yield stress increases as the foam drains and so a good, pourable foam can be achieved by forming lots of smaller bubbles (thinner channels between the bubbles = slower drainage) and pouring it fairly quickly after foaming. But if you wanted to make 3D art of the form in the photo, you would want foam of a different stiffness, a different type of elasticity. You would probably want a drier foam.
In a sense, it is interesting to note that much that determines the response of a substance is about the voids within it rather than purely the material it is made from. Perhaps there is an analogy back to the cafe there: much that makes a coffee shop is the atmosphere created by the cafe rather than purely the coffee and pastries that are stocked. Or maybe that’s one step too far, and we need to go back to ponder and play Under the Willow tree while we enjoy our coffee, foamy or not.
Under the Willow Tree is at 114 Green Lanes, N16 9EH
