Sgwd y Bedol - The Horseshoe Falls

We walked up from Pontneddfechan in the Neath Valley to see the four waterfalls. The Horseshoe Falls in the foreground is well-named. I posted recently about water flowing faster in the middle of a stream that towards the sides. There is more drag from the edges. So i wonder whether faster water wears rock away faster and has resulted in the horseshoe shape?

A wormhole in the Welsh Assembly

 I loved the ceiling in the Welsh Assembly. It reminded me of the diagrams that I see of curved space-time. Those diagrams are used to explain wormholes by making a direct jump across the gap from one part of the curved surface to another. There was a leak in the ceiling and drops of water were moving directly from the top surface to the bottom surface without following the curved path round the wood. That's like a worm hole!

Voids in space at Pont Melin-fach

We walked up to the Pont Melin-fach waterfalls in the Brecon Beacons. A pattern of bubbles was continually forming and dispersing below one of the falls. The bubbles formed along lines with voids between these strings of bubbles. This reminded me of the biggest structures in the Universe. Galaxies are known to form along strings called filaments with huge voids between. In other words, galaxies are not uniformly distributed in the Universe https://en.wikipedia.org/wiki/Void_(astronomy)

Telescopes on La Palma

 I was pleased to see a programme about the telescopes on La Palma last night http://www.bbc.co.uk/programmes/b08f19c3 We could just see them when we visited the amazing Caldera de Taburiente.

 These cliffs are the edge of the caldera and the tops of the telescopes were visible. They are over 2km above sea level so are generally above the cloud. The population of La Palma is small so there is little light pollution. In another life, I will be an astronomer on La Palma.

Blowing the lid off the tin

In this experiment, you fill the tin with gas from the bottom,  ignite the gas and pull out the tube from the bottom. The gas burns with a yellow flame through the hole in the lid for a while. Convection pulls in air through the hole in the bottom. The reaction must head more towards complete combustion because the flame ceases to be orange. Eventually the temperature inside gets so high that the pressure of air particles hitting the lid is too big. The lid almost hits the ceiling. I tried to do some calculations to find the temperature of the gas inside the tin when it explodes.

The tin felt warm to the touch after the experiment so I estimated a temperature rise of 20 degrees Celsius. The method leads to a suggest that the temperature of the gas rose by over 20000 degrees Celsius. This is clearly not true so there must be a flaw in the logic somewhere. I have assumed that all of the energy released by combustion goes to heat the tin and the gas inside it but the flame is burning outside so this assumption is flawed.

Nordpark fountains in Dusseldorf again

I've been thinking about why the beam of water from the fountain spreads out as it goes through the air and doesn't stay as a narrow beam. I suspect that it is because the water flows through a pipe so that the water nearest the outside of the pipe will experience friction and move slightly slower than that at the middle of the flow. The slower water won't go as far. If the water is projected at angle theta to the horizontal, then horizontally the water will have speed v.cos(theta) and vertically v.sin(theta). Vertically, it will reach its highest point after time t=vsin(theta)/g and symmetrically will mean it hits the bottom after time t=vsin(theta)/g. Assuming horizontal speed is constant then distance horizontally will be v.cos(theta).t = vsquared.sin(theta)cos(theta)/g. The ratio of biggest speed/smallest speed will then be square root (smallest distance/biggest distance). For the fountain in the bottom left hand corner this will be about 1.07. The speeds are not too different.

Pressure Law gas leak

I tried to do the Pressure Law experiment. It hadn't worked the year before and I worried that the range of temperatures wasn't high enough to produce a convincing and measurable rise in pressure. The scale divisions are every 20 kPa (red scale - see below)

Normal atmospheric pressure is just over 100 kPa at say 25 degrees Celsius lab temperature. I used boiling water to raise the temperature of the air inside the flask to 100 degrees Celsius. We waited long enough to allow there to be equilibrium between the water and the air temperature. p1/T1 = p2/T2 gives 100/298 = p2/373 as the temperatures have to be given in Kelvin. The higher pressure will be 125 kPa so over a (wide) scale division higher. It would be measurable. But the needle didn't move. There must be a gas leak causing equalisation to atmopsheric pressure (ie it's not a closed system). So this week I tried sealing the gaps with Vaseline which worked for half a minute and then the leak returned.

Overly precise knitting needles

This massive wooden knitting needle came as part of a kit. 20.0mm seems a little over precise. It might suggest that the diameter is precise to the nearest 0.1mm as measured with a micrometer screw gauge or Vernier callipers. It could mean precise to the nearest 0.5mm, as in 20.0mm not 20.5mm. That's where we need some steer in the form of stated precision, eg 20.0 +/- 0.1mm for example.

Resistivity research sources

Transformer oil
https://www.diva-portal.org/smash/get/diva2:829952/FULLTEXT01.pdf
https://en.wikipedia.org/wiki/Transformer_oil_testing

Oil drilling well logs
http://petrowiki.org/Well_log_interpretation
http://www.cgg.com/en/What-We-Do/Onshore/General-Geophysics/Survey-Technologies-and-Applications/Resistivity

Speaker wire
http://www.radio-electronics.com/info/formulae/resistance/resistivity-table.php
https://www.cambridgeaudio.com/blog/speaker-cables 
https://en.wikipedia.org/wiki/Speaker_wire

Earthing for power lines
https://www.bgs.ac.uk/research/environmentalModelling/geoproperties/Resistivity.html

Corrosion resistance in alloy cars
http://www.cabotcorp.com/solutions/applications/industrial-rubber-products/electrical-resistivity

Four probe method
http://vlab.amrita.edu/?sub=1&brch=282&sim=1512&cnt=1
https://en.wikipedia.org/wiki/Four-terminal_sensing

Wenner method
http://civilblog.org/2015/04/18/electrical-resistivity-test-of-soil-geophysical-method-of-soil-exploration/
https://en.wikipedia.org/wiki/Soil_resistivity

Surface and volume resistivity
http://www.intertek.com/polymers/testlopedia/surface-and-volume-resistivity-astm-d257/
http://www.trekinc.com/pdf/1005_Resistivity_Resistance.pdf
http://four-point-probes.com/volume_surface.pdf

Contact resistivity
https://www.corrosionpedia.com/definition/319/contact-resistance
https://arxiv.org/ftp/arxiv/papers/1008/1008.1826.pdf

Making marmalade: heat of solution for sucrose

I made my first successful marmalade yesterday. I became aware recently that the process of dissolving can have implications on the temperature of an aqueous solution. This is called the heat of solution and is in part linked to the breaking of bonds if an ionic compound dissolves. Sucrose is not ionic and doesn't dissociate but is endothermic on dissolving. When I add the sugar, the process of dissolving should lower the temperature. The molar mass of sucrose is 342 grams. I dissolved nearly 800 grams which is 2.3 moles. The heat of solution is 5.4 kJ per mole so it took in about 12 kJ. I was using 1700 ml of water so 1.7 kg. Using the specific heat capacity formula E=mcdeltaT, the decrease in temperature would be 12000/(4200*12) = 0.24 degrees Celsius. It wouldn't be noticeable. My sources were http://webserver.dmt.upm.es/~isidoro/dat1/Heat%20of%20solution%20data.pdf and https://uk.answers.yahoo.com/question/index?qid=20131019111912AAvjNHf

Venus gets closer but doesn't get brighter

Venus is a very bright object in the evening sky at the moment. Having a closer orbit to the Sun, it takes less time to go round and so comes past us on the inside. It is doing just that at the moment. It is approaching its closest point which is when it will be exactly between us and the Sun. Normally objects get brighter as they get closer. But we will be more and more looking at the back of the planet so it will be darker and darker. Hence Venus won't get brighter as it gets closer - it should stay at the same brightness as it goes past.

Rime ice on The Calf - which way the wind blows...

I've posted about rime ice before but found this wonderful example on The Calf in the Howgills. It occurs when the wind is blowing supercooled water vapour. This is when the water vapour has made it below the freezing temperature but has been unable to turn solid for lack of a nucleus on which crystals form. The water vapour freezes solid onto the first surface it hits, so the rime ice grows into the wind. I stood with my back to the wind to take the photograph. This is HARD RIME. My job now is to find soft rime.

Light escaping from an optic fibre

I love this optic fibre demo. It is just a bent piece of Perspex. The Perspex has a higher refractive index than the air so light speeds up as it leaves the Perspex. If the angle is big enough, bigger than the critical angle, all of the light reflects back into the glass and thus is able to zig-zag round the curve to emerge at the end.
                                                
 But look - light does escape out of the side of the fibre on the most curved sections. You can see that these parts are lit up.

I have reasoned that this is because when bent there is less space to fit in light between the critical angle and the top of the fibre so more of the light is below the critical angle and escapes.

Electrolysis with a Schnee Bath in Woodhall Spa??

We went to Woodhall Spa in Lincolnshire to look for a bird on the River Witham. I was intrigued by the history. Woodhall Spa's prosperity was based on a failed coal mine that released mineral waters. But it was the Schnee Bath that really got me thinking. As far as I can tell from a little poking around on the Internet, each limb was placed in a porcelain dish which was filled with warm spa water. It appears that the electric current was passed through the mineral water and not directly through the body, but I can't be sure of this. So they would be performing electrolysis on dissolved aqueous salt solutions. Again, it is not specified which metals had bromide and iodide salts but would be likely to be potassium or sodium. So say we had the following ions in solution: K+, Na+, Br-, I- and from the water H+ and OH-. Halide ions would be attracted to the anode so you might well get bromine gas! K+ and Na+ are more reactive than hydrogen so you'd get hydrogen at the cathode. Sounds dangerous but it clearly wasn't instantly fatal. Anyway, we did find the White-billed Diver: