Gullet Quarry in the Malverns

 Gullet Quarry in the Malverns is a geological marvel but you can't get to it because of the fencing installed to deter swimmers. The Malverns themselves were formed as igneous rock deep underground over 600 million years ago. Later sedimentary rocks formed above them. When Africa crashed into Spain, the old igneous rocks were pushed up through the earth. There was clearly metamorphic processes at play because gneiss was formed - I didn't know it existed south of the Outer Hebrides. The sedimentary rocks eroded away more easily and that is why the Malverns stand out as a distinct range. I found out a lot from Ronald Turnbull's wonderful book, Granite and Grit. The photograph below shows pinkish rocks. This will be the pegmatite. He says "where gneiss is crushed and heated to the verge of melting down and starting all over again, the rock called pegmatite is formed". Slow cooling means even bigger crystals than in granite.

The next two pictures show the unconformity which helped geologists to work out what happened to the Malverns. The gently angled rocks in the trees are sedimentary and they are at a wildly different angle to the tilt of the igneous and metamorphic rocks.

Kelvin-Helmholtz clouds

Trawling back through recent photos I found this one that I took at Scarborough in May. I took it because the rippled edge of cloud looked interesting. After my research into the wave clouds in Scotland, I now think that these are probably going to be Kelvin-Helmholtz clouds, but not as good as the best examples. https://en.wikipedia.org/wiki/Kelvin%E2%80%93Helmholtz_instability

Sands of Luce: kite buggies and components of force

We enjoyed watching the kite buggy racing on the beach at Sands of Luce. In the picture the wind is coming towards me bu the buggies are moving left and right. The kites are rigged to be pushed at an angle to the buggy's direction of motion that is less than 90 degrees. This means that you can resolve the tension in the strings to one component along the direction of motion that makes the buggy moves forward and one force perpendicular to the motion that will try to pull the buggy over. Inspection through binoculars suggests that the kite is not the same on both edges and is wing-like. Pulling on the strings means it catches the wind differently to enable the pull from left to right or from right to left. It seemed very skillful with the drivers concentrating more on the kites than the direction in which they were going!

More questions about the Belt of Venus

I watched the Belt of Venus for some time at sunset. It is finally beginning to sink in that these are not clouds on the horizon. The sky looks blue during the day because oxygen molecules scatter the blue wavelengths back in our direction. The Belt of Venus is the pink band between the lower grey shadow of the Earth and the blue sky above which is still fully lit by the Sun. Accounts say that it is pink because of back scattering of red light from the Sun. So why isn't red light scattered back all the time? Is it because we are low in the atmosphere at this time and dust is now important? That's what I'm struggling with. Why isn't there any blue left if it is still being lit by the Sun? I've looked at a lot of articles and not had any definitive sense. They say the Band is between 10 and 20 degrees. My fingers would roughly agree. My next source for research will be https://en.wikipedia.org/wiki/Absorption_band since the Chappuis Effect was mentioned in one forum as contributing to the grey colour below the band. This was being disputed but at least gives me something to go on.

Cloud waves over the Machars

 If you look at this view from Sands of Luce, it looks as though there are 4 evenly spaced cloud covered hills in the distance. The view below was taken a day later: there are not 4 evenly spaced hills. The original pattern looked suspiciously like a stationary wave at ground level with a fixed wavelength that must have been some miles long. The day in question was one of much visible evaporation at ground level on the beach. The air over the Machars must have been saturated with water vapour.

I have not been able to find any identical pictures but I did find this: https://communitycloudatlas.wordpress.com/category/kelvin-helmholtz-waves/ If you scroll down to the diagram of how the waves form, it looks like the picture for "small disturbances". I can make a case that there was a lower layer more dense because it was laden with water vapour and moving more slowly because of proximity to the ground. A layer of faster moving air above would lead to a wave pattern forming. I think it now helps me to understand the ribbed patterns in high clouds as well.

Sands of Luce: ripples in the sand

It was very windy on the beach near Stranraer. I noticed that the sand was piling up in ripples like a regular waveform with the wavefronts running perpendicular to the wind direction. I found a brilliant article that explains why https://www.scientificamerican.com/article/why-do-regular-wavelike-s/ In short, the wind gets strong enough to get some sand grains airborne. They hit the ground at a shallow angle and this knocks other sand grains forwards, but only by a small amount. It means that sand is constantly knocked forward a few millimetres at a time on the gently angled slopes facing the wind but there are fewer impacts on the steeper slopes angled away from the wind. It is harder to dislodge sand from there so they define the end of the ripple.

Stable stones on Allonby beach

Mrs B built this stone tower on the beach. The rule I teach for stability is that the line of action of the weight acting from the centre of mass must pass through the base area. So how does that apply here? Is it that for each extra stone added, its line of action of weight must pass through the bottom stone's base? That appears to be the case here. If you just went for each stone's line of action passing through the base of the one below, you could build a tower leaning out sideways and that couldn't happen. This structure curves back inwards at the top to achieve balance. My second and perhaps better thought is that it depends on moments about a central axis that might well include the centre of mass of the whole structure. Mass x distance left and right of that would have to be equal.

Towing a glider at Pulborough Brooks

Somewhere in the picture is an aeroplane towing a glider. The driving force on the aeroplane is from the engine. This will have to overcome air resistance on itself as well as that of the glider. At constant speed the engine force must equal the counter forces on the aeroplane. The tension in the tow rope would then merely need to be equal to the size of the drag forces on the glider. I was wondering whether the rope would go slack at constant speed but since the glider experiences drag, that can't be true.

Northcott Mouth: quartz cooling joints

I noticed this quartz vein and how the mineral is split perpendicular to the vein. I think that basalt shrinks as it cools pulling inwards and I wondered whether that is what is happening here.

Kinder Reservoir

I always like some numbers to interrogate. I was excited to notice a statistic about litres per day released from the reservoir but it's not the water extracted for people but that additionally allowed to flow on to keep the River Kinder moving. However, I have found that the reservoir serves 340,000 people http://corporate.unitedutilities.com/1511.aspx so using the idea that the average person in the UK uses 150 litres per day, we can estimate that 51 million litres per day are extracted for people. That is just over 2% of its capacity. If the catchment area is 866.7 hectares and a hectare is 10^4 square metres and that 51 thousand cubic metres are extracted per day (1000 litres in a cubic metre) then it lowers the water table by 51000/8667000=0.006metres or 6mm a day. This is similar to the number I got for the water extraction in the Forest of Bowland last month.

Edward Elgar: Enigma Fountain in Great Malvern

 I've always loved Elgar's Enigma Variations so I was interested to find this fountain in Great Malvern. Water pressure on Earth is dependent solely on the height (OK, it's height x density x gravitational field strength which is why I specified water and Earth). The water gets pushed up 3m so it must have started 3m up the hill behind me. We climbed to St Ann's Well which was much higher than 3m up though. I was also interested to note the way that the water follows the inside of the arch after being released under the point of the arch. I'd say surface tension is keeping it attached to the stone but I normally use that to describe the water/air interface - the way that water pulls back in on itself and doesn't attach to the air. Here, the water has a force that attaches itself to the stone. So is that surface tension?

Brentor: basalt under the sea

Brentor is an amazing location. A little church perched on the top of a tor. But it is even more special because unlike Dartmoor itself, which is an igneous intrusion, Brentor was a volcano in the sea producing basaltic lava flows on the surface. Basaltic lava in the sea produces what they call "pillow lavas" after the shape of the deposits but apparently that didn't happen here http://www.devon.gov.uk/geo-brent-tor.pdf and http://www.dartmoor.gov.uk/learningabout/lab-printableresources/lab-factsheetshome/lab-geologylandforms

Resonance: 90 degrees out of phase

 I set up coupled pendulums. I set one pendulum off. It wobbled the connecting string along the top which forced the second pendulum to move. Since they were the same length, the second pendulum was being forced at its natural frequency which meant that large amplitude oscillations were the result. The system is complicated in that the first pendulum transfers its energy to the second, so that the first one stops. Then the second pendulum transfers the energy back. There is a phase difference of pi/2 radians or 90 degrees between the driver and the driven. In the picture below you can make out one blurred pendulum level with the clamp stand in the middle of the oscillation and the other at amplitude on the right.

Castle Drogo: Biomass boiler house

 Another example of renewable energy being used. The poster claims 690000kWh. I take it that means per year, although it does not specify. 690000/(365x24) = 90kW which sounds realistic if it were running all the time. But say electricity were 10p per kWh, it would represent £69,000 a year of heating.

The diagram suggests that the system is 94% efficient.

Castle Drogo: thermal expansion and asphalt

The main problem with the roof has been the very early use of asphalt for a flat roof, before its properties were fully understood. It expands on hot days and contracts on cold days. This makes it crack and let water through. I was interested to look up the coefficient of thermal expansion because I have never really studied it. Turns out it is measured in units of "per degree Celsius". Length doesn't come into it because it is calculated as expansion per unit length - in other words, it is a strain. https://en.wikipedia.org/wiki/Thermal_expansion A brief internet survey suggests that asphalt may be non-linear and complicated. Here is one source https://d3dqsm2futmewz.cloudfront.net/docs/smartWebArticles/mat_thermprop.pdf If the coefficient is say 4 x 10^-5 per degree Celsius, the max imum temperature range between hottest summer and coldest winter might be 35 degrees Celsius. Over a 10 metre roof section it could mean a change in length of 14mm. That's quite enough to make big cracks.

Castle Drogo: water pressure on the granite

Castle Drogo near Okehampton is an amazing modern creation by the architect Lutyens. It is less than a century old but has had problems with water penetration almost since it was built. I went up the scaffolding observation tower to see what they are doing. I was told that they have found that even granite can be penetrated by water if it under enough pressure. They have recorded 90mph winds and say water penetration is between 10 and 20mm. 90mph is 144km/h or 40m/s. Take a rain drop of diameter 2mm. That is a volume of 4 x 10^-9 cubic metres and a mass of 4 x 10^-6kg. Change in momentum on impact assuming it is stopped would be 1.6 x 10^-4kgm/s. Now suppose it takes 0.01 seconds to stop the drop. Rate of change of momentum is 0.016N. Area = 3 x 10^-6 square metres so pressure = F/A = 5000 Pa which is 0.05 bar. Mains water pressure is given as 1 bar. If the raindrop is stopped in a much smaller time, then the pressure will be greater.

Electric wind on the Van de Graaff Generator

I put a bar over the top of the VdGG with spikes at each end pointing in opposite directions. It span very quickly. The spikes have such a strong electric field that they are able to ionise the air molecules and then repel them, creating a flow of ions or "electric wind" that you can feel with your hand. By Newton's Third Law, if the air is pushed one way then the spike must be pushed the other way. The two spikes produce a couple that is able to get the bar moving.

Ticker timers

This is one of the classic bits of Physics equipment. An electromagnet is connected to alternating current. The electromagnet then turns on and off at 50Hz. It attracts a metal bar down when it is on which applies pressure through carbon paper onto a paper tape. When the electromagnet is turned off, a spring forces the bar back up. Thus a dot is made on the paper 50 times a second. Traditionally the paper is pulled through by a dynamics trolley. The dots get further apart as the trolley goes faster. The analysis is carried out by dividing the tape up into 10 gap lengths, each representing the distance travelled by the tape in 1/5th of a second. These can be stuck end ways on to make a bar graph that is a velocity-time graph for the motion.

Fidget spinner and conservation of angular momentum

These have been all the rage. As far as I can see, the trick is that if you get it spinning and flip it upside down, it seems to be spinning in the opposite direction. The spinner has mass set a distance from the axis of rotation so it has angular momentum when spinning. Angular momentum is a vector which has a direction clockwise or anticlockwise. This will always be conserved unless a resultant torque acts. So angular momentum will be same when flipped upside down. It will be spinning in the same direction but viewed from the other way up it will look as though clockwise has become anticlockwise. It's just your viewpoint that has shifted.