Popping the cork - Paul's last Wainwright

The weather was exciting for Paul's last Wainwright on Place Fell. Here's the Prosecco being popped. I was being asked last week about how a cork is fired from a bottle. The gas inside needs to have a higher pressure than the air outside. That's not difficult to achieve. But it also important that the difference in pressure provides a resultant force that is greater than the frictional force of the cork against the side of the bottle. The cork is wired on just in case but the cork stays in place even when the wire has been removed. It is necessary to edge the cork out slightly. By doing so, the area of contact between the cork and the glass is reduced so the overall frictional force is reduced. When the resultant force due to the pressure is greater than the friction, the cork flies off. There must come a point when the friction is reduced to zero but the resultant force is large to fire the cork a long way. The parabola was impressive! And congrats to Paul on the achievement!

Magnetic field in a solenoid

I set up this circuit to investigate the magnetic field around and through a coil of wire. Such a coil of wire is called a solenoid. I used plotting compasses to show the direction of the field. First it is important to show that the compasses all point north when the current is turned off. To emphasise this I set up the solenoid along an east-west axis so all the compasses shown point across the axis.

Then I turned on the current. The compasses inside the solenoid point right, along the axis of the solenoid. Those above and below point left. the conclusion is that magnetic flux goes one way through the centre of the coil and then loops back round the outside of the coil. Thus there are said to be circuits of flux flowing through.

 Then I reversed the current and the magnets all dutifully pointed in the opposite direction.

Magnetic field patterns

Single magnet pattern with iron filings

 Attracting poles

 Repelling poles

 The compasses show the direction with arrows going from north pole to south pole.

Phyllite rock layers at Kintra

The geology of Islay is very complicated. I was very taken by the twisted layers in these rocks at Kintra. Look also at the general angle of the layers in the wider picture. In the top picture, the layers seem to go through a 90 degree angle. I was hoping for an unconformity but they are all the same type of rock, just hideously twisted. The rock is called phyllite. It is a form of metamorphosed slate. I read that in slate, clay molecules line up in a preferred orientation. In phyllite it is small crystals of mica. That sounds like schist, but apparently the trick in schist is that it is larger flakes of schist that line up. My source says that the foliation (layering - from the word for leaves) is "crinkled or wavy in appearance" which indeed it is. https://en.wikipedia.org/wiki/Phyllite    http://earthwise.bgs.ac.uk/index.php/Appin_Group,_Grampian_Caledonides

Radiation fog

We found this article this morning http://www.mirror.co.uk/news/uk-news/radiation-fog-descends-uk-met-11459412 It's almost like a scare story. These days the word "radiation" is synonymous with radioactivity. But radiation surely means stuff that travels in rays - ie in straight lines. The physics behind this phenomenon is that solar radiation is absorbed by the ground during the day. The ground gets a bit warmer so it radiates infra-red back upwards. It is acting as a "black body" in the technical physics definition of that term, which derives from the observation that black cans of hot water cool faster than silver cans of hot water. On cloud-free nights, the infra-red radiation is free to pass straight back out into space. So the surface of the Earth cools enough for water vapour to dip below the dew point and it then condenses into fog. Fog caused by cooling due to infra-red radiation disappearing into space.

Looking for green at sunset over Islay

I was fortunate to see the green flash earlier in the year but have since read that it is possible to see colour separation before sunset if you project the image of the sun. I tried it here with the sun setting over Port Askaig on Islay. All I had on which to project the image was my hand. The image was inverted - you can see trees along the top of my hand. I was unable to spot colour separation along the top of the sun with this set up but will persevere.

AM aerial at Feolin Ferry, Jura

This is the view looking north up the Sound of Jura. Notice the thin black line going diagonally from top left of centre down and right. I took the photograph through the car windscreen. When we first bought the car, we thought that the windscreen was cracked. It turns out that the wire they use as the aerial is now discreetly hidden in the glass. Electromagnetic radio waves make electrons oscillate and that is how that are detected. The movement of the electrons constitutes an alternating current. With AM, the amplitude of a given carrier frequency is changed to mimic the voices being carried. The wire represents one quarter of a wavelength. It is about 50cm long so a wavelength would be 2m. Frequency = wave speed/wavelength = 1.5 x 10^8 or 150 Megahertz.That would make it FM though!