Finely balanced on the new Forth Road Bridge

The new Forth Road Bridge is taking shape. The support columns are in but not joined. They are building the road deck outwards from each one and eventually the sections will join up. Notice that the method involves balancing the deck equally on each side. There will be no resultant moment so the column will not fall. Each section is a cable-stay design. The diagonal stays have a vertical component compressing the concrete in the column. Concrete is strong under compression. The horizontal components are equal and opposite pushing in on the column from left and right. The final thing to note is the weird picture effect. The car was moving from right to left. The tops of the cones are bent out of shape. I think it suggests that the camera reads the CCD row by row from top to bottom because the bottoms end up lined up with the column, The cone would not have been thus aligned when I first started taking the photograph.

Wilberforce Pendulum: a chance encounter in Stonethwaite, Borrowdale

 We didn't even know that there was a church at Stonethwaite but we went in for a look and found the above memorial on the wall. I'd never heard of him but looked him up https://en.wikipedia.org/wiki/Lionel_Wilberforce I'm always impressed by anyone who worked with JJ Thomson but I'd never heard of the Wilberforce pendulum. Here's a film of it in action https://www.youtube.com/watch?v=S42lLTlnfZc It is a couple oscillator the sends the energy from up and down vibration to rotational motion and back again periodically. I want to make one now! The churchyard also has the grave of fell-running legend Bob Graham!

Alexander Buchan, isobars and Loch Leven

I had never heard of Alexander Buchan but it is claimed that he was the first to make a scientific weather forecast based on weather charts he developed. Iso in Greek means the same. Isobars are lines that join up places with the same air pressure. They look like contours on weather maps. He was the first person to draw these. He was from a village on the other side of Loch Leven under the impressive basalt outcrop in the photograph. I was pleased to hear that he was a key mover in the building of the Ben Nevis weather station. Read more about him http://www.weathercast.co.uk/weather-news/news/ch/23ba64ba62807a6e3d649985141b30d3/article/alexander_buchan-1.html and https://en.wikipedia.org/wiki/Alexander_Buchan_(meteorologist)

Low Ling Crag roche mountonee on Crummock Water

I'd been wanting to visit this feature on the far side of Crummock Water for years. Now I've been. There has been some argument on the Internet about whether it is a roche moutonee. What's the evidence? They form when a glacier goes over hard bedrock. The glacier here would have been flowing from right to left. The glacier smooths the approach side into a smooth ramp. Coming over the top, the pressure melts some of the ice which then runs into crack in the rock. This water then refreezes and gets pulled by the glacier. This rips the downstream side into a crag. Well, that seems correct with what's in the photograph. There is a diagram here https://en.wikipedia.org/wiki/Roche_moutonn%C3%A9e#/media/File:Roche_moutonn%C3%A9e_eng_text.png As to why ice melts under pressure, that's another story...

Radioactive decay dice

Today we did the experiment that models radioactive decay. We have wooden cubes with one side coloured in. All 30 dice are thrown together. The ones that fall with the coloured-in side upwards are deemed to have decayed and are thus removed from the set. The rest of the dice are thrown again and so the pattern repeats. We count the number of dice left in each time and plot a graph of that against throw number. The result is an almost exponential graph but with a lot of anomalies because the sample size is so small. Today one team did something I've never seen before:

They stacked up the dice removed each time to make a 3D bar graph of dice removed against throw number (on the horizontal axis). In theory, 1/6 of the number of dice thrown should be removed each time. This worked on the first go because 5 is 1/6 of 30. That left 25 dice to throw and 1/6 of 25 would have meant 4 dice removed on the second go. That clearly didn't happen. But the trend is towards an exponential decay graph. A much larger number of dice would be needed to get a truer pattern. I thought this was a wonderful way of presenting the data. :D

Inside an old hard drive

I took apart an old hard drive. The silver disc that is reflecting my camera is called the platter. This is made of a non-magnetic material like aluminium or ceramic with a thin magnetisable layer on the surface.

 The actuator arm has a very tiny electromagnetic coil on the pointed end. It is called the read-write head. If current runs through this, it acts as a magnet and magnetises sections of the platter below. When reading data, the magnetised sections moving below it cause electromagnetic induction to take place. An emf is induced which causes a current to flow in the read-write head and the computer can pick up the data.

 There are strong permanent magnets in the corner with what is called a voice coil between them. When current flows in the voice coil, it attracts or repels from the permanent magnets and can thus move.

The magnetic circuitry must be very sensitive and will deserve testing next time one comes my way.

A couple in Grizedale Forest

We found several of these on a walk in Grizedale Forest. Turning forces are given several different names most notably moment and torque. This is a COUPLE. A couple is when two equal but opposite forces, one on either side of the pivot, push the object round. To calculate the size of the couple you do one force x the distance between the forces. Since the individual moments of each force = force x distance from pivot, but the distance between the two forces is twice the distance from each one to the pivot, the formula for a couple is just the sum of the two moments.

Gravitational waves

It's not every day that Physics is front page news or the main item on the BBC Six O'Clock News. But here we are a week after the big announcement. I have posted before about Einstein's view of space-time as like a stretched out rubber sheet http://wigtonphysics.blogspot.co.uk/2013/10/playing-with-space-time.html The gravitational waves idea is that massive objects cause ripples that travel through space-time like they would across a stretched rubber sheet. The equipment involves two very long laser beams at 90 degrees to each other. The beams are supposed to run in phase. If one arm gets stretched by the gravitational waves, the laser beams will be out of step when  they meet. This can be detected. I was interested in the idea that the ones detected came from colliding black holes. I was surprised they could claim the device had much directionality. However, I see that they detected the same pattern using two devices on opposite sides on the American continent with a short time delay between them. That's how they could postulate a direction.

Reflecting telescope for looking at stars

This telescope was called Stargazer. The end is open and looking down, you can see a reflection in  a concave mirror at the bottom. The purple colour is my camera! The mirror focuses the light onto a second mirror and thus into the eyepiece. This version is called a Newtonian Reflector and is the simplest reflecting telescope. The secondary mirror in the middle is a plane mirror. Other versions use convex mirrors and have the eyepiece at the bottom. Using mirrors removes the possibility of chromatic aberration that affects refracting telescope lenses. The edges of the lens act like prisms and split the light up into colours at the edge of the image. But curved mirrors can suffer from spherical aberration unless they are parabolic because spherical mirrors have multiple focal points.

Oxford United cause chaos at Morecambe

Chaos Theory in Physics is the idea that there can be stable conditions that can go round and round without ever repeating the same precise pattern twice. The weather is an example: it does the same sorts of things every year but is never perfectly identical to previous. The weather has been stuck in a pattern of gales driven by a jet stream somewhere above the northern UK. Hopefully something will happen to disrupt this current stable pattern of bad weather, In terms of Physics, you'd say that the weather would be nudged into a different strange attractor. 20 years ago New Scientist did a lovely piece about Chaos Theory and football in time for Euro 96. Saturday's game at Morecambe was in this vein. The first half was stable pressure from Oxford. Morecambe made early substitutions to try to push the play from that strange attractor. They moved Ellison to the other side of the pitch and even brought off their goal scorer. It worked. After half time, the game settled into long ball and Oxford looked rattled. Michael Appleton made some changes and suddenly Oxford were playing through the middle again, running out 4 - 2 winners. Chaos Science is also called Complexity. There are so many variables but we look for stable states and study how to move from one to another. The article is here if you want to pay to read it in full https://www.newscientist.com/article/mg15020333-800-chaos-pitch/

Polarised sky at St Bees

As has been discussed before in this blog, the sky appears blue because of the scattering of light from the Sun by nitrogen and oxygen molecules. They are small compared to the wavelength of the light and you get Rayleigh scattering  https://en.wikipedia.org/wiki/Rayleigh_scattering#Reason_for_the_blue_color_of_the_sky
This is because the electric field in the light wave excites electrons in the molecules. As they de-excite, a photon is re-radiated but in many directions. If you turn so that your shoulder is lined up with the Sun and twist a polarising filter through 90 degrees, the blue sky goes from light to dark. It is polarised. Compare the sky on the pictures below. The Isle of Man was showing well!

Then I stood with my back to the Sun and repeated the trick. No difference in the sky.

Apparently it is because at 90 degrees to the Sun you are looking at photons sideways on so they will always line up in the same plane. See the animation on this site  https://www.polarization.com/sky/sky.html  I will have to think about this because how can we see it if it isn't coming towards us? Or is it polarisation of the waves that don't come to us?

Sky Tower at Leighton Moss: gravitational potential energy

We were able to go up the new Sky Tower on the RSPB nature reserve at Leighton Moss near Carnforth. It is 9 metres high. I had to do work against gravity to climb it. Suppose my mass is 100kg. That means that my weight is 10x bigger on Earth - weight meaning the pull of gravity on my mass. So my weight is 1000N. I do work against this 1000N force. Work done = force x distance moved = 1000N x 9m = 9000J of work done. This then becomes the energy stored by climbing - gravitational stored energy. I can get that energy back when I come down.

Current balance

 I clamped an aluminium bar over a chemical balance. There was a strong magnet on the chemical balance. I zeroed the balance. I chose aluminium so that it was not attracted to the magnet.

 Then I ran a large electric current through the aluminium rod. Suddenly we got a reading on the balance. This is because the current has its own magnetic field that repels the magnet. Thus the magnet pushes down on the balance.

I swapped the electrical connections over so that current flowed the other way. The reading on the balance became negative. This time the current's magnetic field was attracting the rod. If you use a potentiometer, you can vary the current through the rod. Plotting a graph of current against force as measured by the balance will show that the two are proportional. This is why it is called a current balance: every force reading can be converted into a current.

Large surface area in St Mary's

The radiators in church are essentially very old-fashioned convection heaters. Hot water heat touches the metal from the inside and transfers thermal energy to the metal by conduction. The metal is a good conductor because free electrons are able to go racing through the structure and collide with ions, making them vibrate faster than waiting for the usual domino toppling model. The hot metal transfers thermal energy to the air. The air expands, becomes less dense and rises, which is supposed to warm the air in the building. A high ceiling is not a great idea! But the intricate shape means a larger surface area of hot metal touches the air at once so the rate of energy transfer from metal to air is greater.

Calm sea in Silloth

For some time I have been interested in the idea that the sound of the sea at Rhosilli camp site last summer was as loud as the wind  turbine at Kessingland. So I've been out with my deciBel meter. Trouble was the sea was very calm when we went to Silloth. I went right down to the edge of the sea.

 66 dB is about as loud as a conversation.

You couldn't even see the sea up in the car park. It suggests the sea was as loud as a refrigerator hum or even rustling leaves. It was louder at Rhosilli!

Polarisation in Wigton

I was talking to my class about the picket fence model for polarisation. Transverse waves are ordinary wavey-looking waves like the waves on the sea. Waves that vibrate in the vertical plane would be able to slip through the gaps between the fence posts. Waves vibrating in the horizontal plane would not. It's a good model but more complicated than that in real life. If the electric field of an electromagnetic wave lines up with the poles, which could be metal or organic molecules, it makes electrons in the poles oscillate so using up energy and thus stopping the vertical electric field electromagnetic waves. Ones with horizontal electric fields can only make electrons vibrate a tiny lateral distance in the poles, thus horizontal waves can get through. This is opposite to the picket fence analogy!

Standard wire gauge and knitting needles

I went down to the library to join the knitting group. You can see my efforts at the top. Knitting needles are now measured in mm - their diameter. I am using 4mm needles. My micrometer screw gauge reads 4.01mm so the needles are accurately labelled! Older needles have a more archaic numbering system which means that the thinner the needle, the bigger the number. It turns out they used to be measured in standard wire gauge. A "28" needle, if it existed, would be as narrow as the copper wire pictured. My 4mm needles would be 8 in standard wire gauge. If you want the history of wire gauge, try this https://en.wikipedia.org/wiki/Wire_gauge. Basically, the number told you how many times the wire had been pulled through the machinery. Each pull made it thinner. Hence bigger number, thinner wire.

Stationary wave on the M6

One of the joys of motorway travel is getting stuck in queues. You can be there for half an hour making very little progress. You get to the front of the queue thinking there must have been accident, but there's nothing there and you just drive away. So why were we queuing? There must have been a cause earlier on, like someone braking hard, and then because everyone else braked, a queue develops. It becomes an enduring pattern - a stationary wave. The pattern stays in place on the road even as each individual car moves through it. Eventually it disappears when the traffic density is low enough for the stopping distances to become much bigger.

Crossing the continental shelf

We crossed the edge of the continental shelf. The crust of the deep ocean beds is made of mafic rock like basalt which is denser and sits deeper. The continents are made of felsic rock like granite which is less dense and sits higher. Once the hills like Skiddaw behind Wigton were on the edge of the continental shelf - mudstones deep underwater. Then we collided with Scotland which threw them up as mountains.

The power of water on Catbells

We found this remarkable channel on the path up to Catbells from Grange. I assume it was cut on the floods weekend in December. Look at the stones piled up against the wall at the bottom. Let's say 1 metre high by 10 metres wide 1 metre deep. That's a volume of 10 cubic metres of rock. The density of rock is about 3 tonnes per cubic metre. That's 30 tonnes of rock shifted. Maybe not as much as I'd thought. What impressed me the most is that the water had such power given the short run-off. It looks like it gets about 150 metres of stream bed. I'm thinking about possible equations. I'd like to apply Newton's Second Law as F = v (dm/dt) where the final term is mass flow rate but the velocity of the flow is not constant because it is accelerated by gravity.

Is evaporative cooling responsible for the ice?

Two consecutive days and very different underfoot. My impression was that the air temperature was about the same each day but we were sliding along on sheet ice in the top picture. The top picture came with gale force winds. It was flat calm in the bottom picture. My hypothesis is evaporative cooling. The wind keeps shifting particles away from the surface. This would lead to higher rates of evaporation for water. It is the most energetic particles that escape first. Those that remain have lower energy therefore the temperature is lower and would thus be more likely to freeze.