Looking through the crystal ball

Thanks to Emily for letting me investigate the properties of a glass sphere. It turns the world upside down because refraction in the glass bends light from the top downwards and light from the bottom upwards. This is because light slows down when it goes into the glass and speeds up when it comes out. A sphere doesn't focus the light perfectly to one point but the image is clear so the multiple focal points must be close together in this arrangement. This is called spherical aberration - see https://en.wikipedia.org/wiki/Spherical_aberration for photographs.

Language and Quantum Mechanics: the Hopi Time Controversy

I recently finished Barry Lopez's Arctic Dreams. It's a really interesting book which I know inspired Robert Macfarlane. Lopez did a lot of thinking about the relationship of  native people to the land. He is interested in their languages. In the book, he gives an example from the linguistic study of the Hopi language from much further south in Arizona. When he was writing, it was felt that the Hopi language had limited tenses so that there was little concept of past and future. The hypothesis was that they had no concept of time as distinct from space, whereas in English we can tell from the tenses used that there seems to be a linear flow of time from the past to the future. Lopez felt that this would make Hopi a great language for describing Quantum Mechanics. A little poke around on the Internet reveals that the idea has now become very controversial https://en.wikipedia.org/wiki/Hopi_time_controversy It turns out that Benjamin Whorf, who came up with the hypothesis, was influenced by Einstein, so there is some Physics feedback going on here. It looks like an interesting topic for further reading.

Diode and ac and oscilloscope

I set up an ac signal on an oscilloscope.

I then added a diode to the resistor.

It did seem to chop out the bottom of the signal although amplitude was reduced.

An odd cloud inversion

The cloud inversion on Wednesday was an odd one because when we set off, there was no mist in the valleys. What usually happens is that on a clear night, radiation fog forms in the valleys as the air cools and falls below the temperature at which the air becomes saturated with water vapour. When the sun rises, it heats the upper layers of the atmosphere but the sun's rays can't reach the air in the valley to warm it. Hence warm air is above the cold air. Since it is warm air that rises, the thermal energy can't reach the lower layers and the cloud stays trapped in the valley. The cloud is "inverted". The odd thing on Wednesday was that the cloud began to fill in after I had got so warm in the sun that I had to take my layers off on the ascent. At that point, sunlight wasn't prevented from reaching the valley floor. So did the humidity rise? Perhaps there was more evaporation which increased the amount of water vapour in the air above the amount that the air could hold at that temperature.

Brocken Spectre at last

I've waited years but finally saw my Brocken Spectre with glory. It was a very small and distant example but I'm ecstatic. Here's how the spectre forms:

The glory is formed by refraction of sunlight in water droplets in the mist which is then sent back in my direction, a phenomenon called backscattering https://en.wikipedia.org/wiki/Brocken_spectre

Other reasons that rocks move

I posted this week about rocks being carried long distances by ice. When I read The Pebbles on the Beach by Clarence Ellis last year, he mentioned that sometimes you can be fooled by rocks that were carried as ballast by ships and then dumped. This section of the Tyne near Wallsend was one such place. Thames dredgings mean that some of the rock could be chalk. I didn't go searching because of warnings about chemicals from old lead and tar works. In Physics, the extra mass carried in the bottom of the boat makes it harder to rock from side to side. It would give it a moment of inertia.

Excellent documentary about quantum entanglement

BBC 4 had a brilliant documentary on last night about quantum entanglement. https://www.bbc.co.uk/iplayer/episode/m000db95/einsteins-quantum-riddle Highly recommended.  4 weeks left to watch it.

How do we know which way the ice went?

This is a lump of Shap granite perched on a boulder outside the Natural History Museum in Oxford. It was picked up by a university expedition many years ago ... from a beach on the Yorkshire coast. It had been carried there by ice during the Ice Age. It is by finding distinctive rocks like this that we can work out the directions in which the ice moved. I have been told that there is a lump of our local Criffel granite in the middle of Cannock Chase; I am yet to visit.

Red sky over Silloth

When the sun set over Silloth, I realised I might have misunderstanding something for years. I know and teach that it is air molecules and fine dust in the atmosphere that scatter blue light. At sunset the light travels the maximum distance through air to reach us so all the blue light is scattered leaving the red end of the spectrum. I now realise that I thought the clouds were red because it was they that scattered the light. The clouds are red because they reflect the red light that is the result of the scattering. I think that the give away is that it is the bottom of the clouds that seem red.

How does a digital multimeter work?

It occurred to me that although I have taught how a moving-coil meter works, I don't actually know what goes on inside a digital multimeter. I've read several articles and I haven't yet got a pithy explanation. I think it boils down to a comparison method of turning an analogue voltage into a digital response. An ammeter would then use a the voltage across a known resistor and I=V/R to come up with a value. https://electricalfundablog.com/digital-voltmeter-works-types/#How_does_a_Digital_Voltmeter_Work has 5 principles of operation. https://www.electronics-notes.com/articles/test-methods/meters/how-a-dmm-digital-multimeter-works.php is another good starting point.

Can a measuring instrument be a control variable?

When I asked for the control variables in this experiment to be listed, several people said "same voltmeter; same ammeter". I've been struggling for years to come up with words to explain why the measuring instruments are not a control variable. Today it came to me. With any true control variable, if you shift it to a different value, you change the reading for the dependent variable. With a measuring instrument, the idea is that if you change it to a different model, you should get the same reading. The choice of instrument should not affect the reading and therefore the measuring instrument is not a control variable. In the case of the ammeter and voltmeter, there might be an exception. It would depend on the resistance of the ammeter or voltmeter. In theory, a perfect ammeter has no resistance and a perfect voltmeter has infinite resistance. If this were not to be the case in a replacement instrument, then the readings would change. However, it would have to be the resistance of the instrument that was listed as a control variable.

Atwood Machine

This was in the Whipple Museum of the History of Science in Cambridge. I used to do calculations based on two masses joined by an inelastic cord and hanging over a frictionless pulley. This equipment gets real results for that. Mass M1 is pulled downwards by gravity and upwards by the Tension T. Resultant force M1.a = M1.g - T. If mass M2https://en.wikipedia.org/wiki/Atwood_machine
 says that elevators and funicular railways are approximations to the Atwood Machine.

A pendulum made from a chain

The wind was blowing this gatepost chain above Ennerdale. I timed 22 oscillations in 20 seconds so the time period is about 1 second. I was wondering whether being a chain made of links would affect the motion. If it acts like a simple pendulum, then the effective length will be to the centre of mass. As the mass is uniformly distributed, that will be halfway along the chain. There are 14 links of 4cm each so half length is 28cm. Applying the equation T = 2*pi*sqrt(L/g) gives time period of 1.1 seconds. It looks as though the fact that it is a chain has no effect on its pendulum motion.

Is Floutern Cop a crag-and-tail?

Floutern Cop is a small prominence above the glacial corrie filled by Floutern Tarn. It is long and narrow. The western end is craggy but the eastern ends tapers away. It looks like it might be a crag-and-tail feature. https://www.bbc.co.uk/bitesize/guides/zg36wxs/revision/4 This would mean that at some point there was an overlying glacier moving from left to right in this picture. This probably doesn't fit with the idea of a corrie glacier but I did read in the autumn that corrie glaciers were the last phase of glaciation in the district.

Satellite dish angle above Thirlmere

Coming down Steel Fell to Thirlmere, we came across this satellite dish. It is of course pointing south over Dunmail Raise towards the equatorial orbit but what struck me was that it wasn't really tilted towards the sky. I suppose I'm never normally on a level with them. I found this https://www.uksatellitehelp.co.uk/2007/08/01/the-perfect-satellite-dish-alignment-a-how-to-guide/ which says that the closer you get to the Equator the steeper the angle as you are almost underneath the satellite but at these latitudes the dish can be almost vertical.

Spring on the beach at Allonby

Freshwater was bubbling up through the sand and shingle on the beach south of Allonby. It the flowed straight down to what looks like a wrecked pipeline. I had wondered if it might be an artesian well (see illustration on https://www.yourdictionary.com/artesian-well) but maybe there is an old drainage pipe submerged beneath the shingle whose outer end has broken.