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.