Australian Crunchie is brittle

 

This delicacy tastes like a British Crunchie bar. When teaching, I tend to use Rich Tea biscuits to illustrate brittle failure and Mars Bars to show ductile failure. In brittle fracture, there is no deforming of the material as it breaks so the bits can be put together again to show the whole. I found this nice explanation which is my first introduction to the ScienceDirect website. It looks useful.

Negative space is art not physics

 I was drawn to this recent art installation at Boughton House in Northamptonshire.

It stands opposite a mound made of the earth dug out centuries ago to make the ornamental water features. The mound has the same dimensions up as the hole has down.

The interpretation board mentions it as a "negative space". Now if I were taking space to be a volume, I'd say it was a scalar and could not be negative. So for example with Charles' Law for gases, I plot a line for volume increasing with temperature and then extrapolate backwards to zero volume. That temperature is called absolute zero because you cannot go any lower and have negative volume. I was wondering whether perhaps there might be negative space in General Relativity but I don't think there is. However, it turns out that negative space is a term from art.

How do the lighting effects work?

 We were watching Stables at the Prospect Farm gathering.

This lighting effect looked strangely familiar. It is not far off being the diffraction pattern through a net curtain.

But then this one came up which had me wondering about mirrors like in a kaleidoscope,

There wasn't a brand name on the small cylindrical units that had 3 apertures. https://en.wikipedia.org/wiki/Laser_lighting_display does mention both mirrors and diffraction.

Keeping the temperature of a cactus constant

 Mrs B has just made a cactus pin cushion.

I've been reading Plant Physiology by Salisbury and Ross. They assert that all biological processes can be explained in terms of chemistry and physics. There is a great chapter on how thermodynamics affects plants. They state: "The high specific heat of liquid water is caused by the arrangement of its molecules, which allows the hydrogen and oxygen atoms to vibrate freely, almost as if they were free ions." This large specific heat capacity has implications for organisms like cacti that contain a lot of water. It means that no matter how hot or cold it gets outside over a 24 hour cycle, the internal temperature won't change much.

Why do we draw rays when we can't see them?

 As a child I learned to draw rays from the sun coming from a circle. Here on the lantern in the Wigton stained glass there are rays. But we can't ordinarily see rays so why do we draw them?

Take a look at the second picture here. And I've posted about this camera effect before. I think the answer will be that what we see is affected by diffraction. And here's the reference. It's called diffraction spikes caused by eye lashes or eye lids when squinting. 

Jelly spheres on cup cakes

 A kit from the supermarket gave me my first introduction to spherification. The process makes the little jelly spheres that I used to decorate the cakes. The pictures show the process in reverse.

This is what they looked like after being rinsed. I'm not the only person thinking of fish roe.

The brown bowl contained a solution of calcium chloride. 

I was given a green and an orange solution that contained sodium alginate from seaweed. On adding drops of the sodium alginate mixture into the calcium solution, gel spheres formed. They mostly sank to the bottom but floated if they contained too much air.

As far as I can ascertain, the alginate forms a type of chain polymer and the calcium ions allow cross-links to form between chains to give it some structure. The picture in the kit shows alginate chains arranged in a circle which will presumably be dictated by the surface tension of the drop. Then calcium ions sit on this surface and cross-link it to an outer sphere of alginate chains. There are good food chemistry posts about it all here and here.

Isaac Newton at Campfield Marsh

 I'd never noticed this pebble sculpture of a newt before but I'm always a sucker for anything with a physics label - now named Isaac Newton.

The last word on social distancing

 

Last year I blogged about the way people were inventing units of measurement for social distancing. This is probably the last word on the subject, found at Campfield Marsh RSPB. I like it because it has subunits.

Tindale Spelter and Fume Works

 We were unable to locate the Black Redstart but we did learn something about brass.

The mining activities in the district produced quantities of zinc ore. By the nineteenth century it was possible to extract zinc in the UK and combine it with copper to make brass. The works that did this were in the hole shown and were called the spelter works.

The concrete buildings on the top were twentieth century fume works where waste material from the spoil heaps was vaporised to allow the zinc to be extracted.

My source for the information is here.

Louder than a lawn mower

Our new emergency whistle is 116 dB which is louder than my 96 dB lawn mower. A 20 dB difference means that the sound of the whistle is 100x more powerful than the lawn mower's sound. This means also that the amplitude is 10x bigger. I didn't know the bit about the amplitudes https://en.wikipedia.org/wiki/Decibel

Fixing the cuckoo clock

 

The cuckoo clock works by pulling up a weight on a chain. As the weight falls, gravitational stored energy is transferred to the pendulum which would otherwise lose energy due to friction and air resistance. The problem was that the pendulum kept stopping. I noticed that if I pulled gently on the hanging weight, the tick was louder and it didn't stop so I added an improvised weight as water in a bottle so that it could be changed to find the correct amount. Apparently using a bigger weight is a known way of making an elderly cuckoo clock last for a few years more. I'm not sure how the gravitational energy gets to the pendulum - there could be a spring involved or maybe it is a gear mechanism that is getting worn.

Miniature cantilever on Buck Pike

 

Take a look at the top of the cairn. Someone has been very creative with the Principle of Moments. There can be zero resultant torque here so a large mass of stone on the left must be providing an anti-clockwise moment to balance the clockwise moment due to the stones balanced on the end of the cantilever.

When a log graph isn't quite as useful

 

I normally use log graphs to make curved graphs straight. The Covid data from the Office for National Statistics was impressively straight but it now appears to have peaked. I can't even say that the gradient of the curve is proportional to the R-number. It is a linear relationship and so linked but not directly proportional. So in general, the bigger the gradient, the bigger the R-number. This week's Covid case numbers for England go like this:

So the ONS is lagging the test data by a week. 

Piezometric surface caused the defeat at Flodden Field

 

At the Battle of Flodden Field in 1513, the Scottish army occupied the high ridge in the distance. They had an advantage over the English who were where the memorial stands in the foreground. The Scots were defeated because they advanced down the hill and got stuck in the mud in the dip between the two ridges where their weapons were ill-suited. This is where the piezometric surface comes in.

A piezometric surface is an imaginary line that shows where pressure would take water up to if it were totally free. Notice that this line coincides with the surface in the dip meaning that it would be marshy. The other two points where it coincides with the surface are a spring and a stream.

Resolving power and distant birds

 

Two very tiny soaring birds were just discernible against the dramatic sky this morning. They were probably gulls or buzzards with a wingspan of about 1 metre. I normally use the little finger of my outstretched arm which subtends 1 degree to estimate how far away they are. But the fraction of a degree was so tiny, I couldn't estimate it. I went back to resolving power. I measured the diameter of my pupil and it was 3mm. That gives Rayleigh criterion resolving power for visible light wavelength of say 500nm as 2 x 10^-4 radians, roughly 0.01 degree.

The furthest distance resolvable between the wingtips, shown as stars above, can be approximated by arc length/radius for small angles and conveniently given in radians. For a 1 metre wingspan, 2 x 10^-4 = 1/radial distance. The furthest they could be turns out to be about 5km away.

New Magnetised Target Fusion power station

 

When we were last in Oxford, the headlines were about a new Fusion Demonstration Plant to be built near Oxford. There have been two ways in the past of containing the plasma - strong magnetic fields and inertial confinement, which seems to be firing them into each other like in a hydrogen bomb. This power station will combine the two approaches. The video on the company website explains it quite well. Liquid lead is spun into a cylinder and hydrogen plasma is injected whilst the liquid lead is squeezed into a cylinder. Fusion takes place which heats the liquid lead. The liquid lead goes through a heat exchanger to heat water to make steam. It looks like it is a pulsed system with repeated fusion events.

Fake glacial erratics at Combe Gill Hydro

 

If you look at the picture above, you'll see some pale coloured boulders amid the darker grey of the glacial deposits. Last time I was up on Bessyboot, I posted about Combe Gill Hydro which was being installed at the time. If you look at my old pictures from two years ago, there is a scar where the access road for the construction machinery had been built. I was expecting to be able to use that track but it has vanished. The fellside has been carefully restored and the glacial erratics replaced. This is good. The costs of the restoration will need to be factored in to any economic calculations about renewable schemes like this.