BBC TV programme about our plutonium stockpile

Somewhere in the hazy distance at the back of this photograph, there is apparently a store of 100 tonnes of plutonium. A lot of people round here think that Sellafield is a nuclear power station. That's not true. It deals with the nuclear waste from nuclear power stations elsewhere in the UK, making the waste safe and storing it. One by-product of nuclear fission is plutonium. It is not only highly radioactive but also very poisonous. It can be used as a nuclear fuel but this is difficult. At the moment the suggestion is that it is mixed with uranium to make MOX - mixed oxide fuel. This is not as easy as you might think. There was a BBC TV programme on last night about it. You have 6 days to watch it on the iplayer You only want the first 10 minutes of the programme http://www.bbc.co.uk/iplayer/episode/b04hv65x/inside-out-north-east-and-cumbria-29092014

More thermals on Scafell

Wasdale is becoming like a second home at the moment. This time we spotted a glider high above the cliffs of Scafell Crag. It wasn't a particularly sunny day so I wasn't sure that there would be strong thermals. My new hypothesis is that the air coming in off the Irish Sea is forced upwards by the mountains and that this will give lift. But we were wondering where the glider would be able to land. It's more tricky than a paraglider!

More about cracked rocks

This is a picture of some rocks on the path up Scafell Pike between Lingmell Col and the summit. It has the same sort of regular cracks as the limestone pavement at Malham. These are the rocks that led Mrs B to first float the idea of earth movements being the cause. Although these rocks are volcanic, they are sedimentary in a way. The rocks are called tuff - the are made of settled volcanic ash. Yesterday's limestone is similar in that it is layers, but of the remains of sea creatures. I wonder if the particulate character of the rock means that it cracks easily if it has shear forces applied. This means a force on the top going left and force at the bottom going right, for example. However, tuff is far more resistant to weathering so you don't get the deep grykes. And I was thinking more about the huge mass that I'd calculated yesterday. How is that moved? The answer is by convection currents in the Earth's mantle. Hot magma is less dense and rises. The convection currents drag tectonic plates sideways and this can generate huge forces.

Harry Potter and me: a trip to Malham Cove

This was our first view of the 80 metre high limestone cliffs at Malham Cove. There used to be a waterfall over it at the end of the last ice age.

We climbed up steps to the limestone pavement on top of the cliffs. "I can't believe I'm standing where Harry Potter stood!" said the girl next to us. They used this location for filming The Deathly Hallows.

Limestone pavement is when the top layer of the old coral reef is eroded into blocks called clints. The deep gaps are called grykes. The grykes must be eroded by chemical weathering due to slightly acidic rain and by physical weathering - freeze/thaw. But they are so regular. Look at the lines running parallel to each other. I think that the weathering has happened along pre-existing weaknesses in the rock. I wondered if that had been caused by shear forces due to earth movements.

This is a map from the visitor centre. Apparently the limestone layer was bumped downwards by earth movements due to the North Craven Fault. Then the Middle Craven Fault was produced by earth movements that pushed the cliffs upwards. The cliffs are 80 metres high. It is about 3km between the faults. The Middle Craven Fault is supposed to be 36 km long. The volume of rock moved is thus about 9 billion cubic metres. The density of limestone is about 2500 kg per cubic metre. Thus it has a mass of about 20 billion tonnes. Think of a force that could shift that!

Bizarre condensation on a warm day

Yesterday afternoon looked like this in Wigton.

Mrs B made the following observations:

1. It felt warmer outside than inside the house.

2. Condensation had appeared on the outside of the water butts in mid-afternoon. Note: condensation, not rain.

I am guessing that a warm front passed over. The air behind the front is warmer. Water has a high specific heat capacity so a cold night and morning had left the water inside the water butt chilled. It takes a long time for water to warm up again. But the warm afternoon air was humid and laden with water vapour. When it hit the cold surface of the water butt, the water vapour condensed. This even though the plastic is an insulator. Remember than insulators are just bad conductors so given enough time thermal energy can move through them. The plastic did feel cold to the touch.

 

Transportation at Wasdale Head

 Not much water in this wide stream bed at Wasdale Head. In fact the picture below shows a cairn half way across because there is a path going across most of the time. I must go back when it's been raining heavily. If this gets used to full capacity....

This is looking down half way across. The rocks are still quite angular which shows that they haven't been transported very far. Pebbles on the beach are much more rounded. I'd say that the pebbles in the amazing conglomerate rock at Dunnotar Castle that I blogged about in August were much more like beach pebbles.

The fields often have massively thick walls. The stones were all over the fields and had to be put somewhere when the fields were cleared. I'm guessing that this was glacial deposition rather than fluvial but I might be wrong.

Thinking about X-ray crystallography on Widow Hause

 

Widow Hause is the dip between Graystones and Broom Fell on the back of the Whinlatter Forests. It was pointed out to me that we could see all the way down the line of trees to the valley below, as shown in the middle picture. Then take another step and we're out of line so the light disappears. This reminds me of the diagrams I've seen of rows of atoms. X-ray crystallography was the technique of firing X-rays at the rows of atoms and figuring out the arrangement from the diffraction patterns. It was pioneered by William Henry Bragg, who was born very near Wigton. It got me thinking about diffraction with the trees. For best results with diffraction, we say that the wavelength has to be about the size of the gap. If the gap between the trees in the gap is 2 metres, then that's the wavelength. These would be VHF radio waves - you'd know them as FM frequencies. But would they really diffract? Since the radio in my house can pick up a signal indoors, I suspect that the radio waves might just go through the trees.

Water feature in Slab Square, Nottingham

Slab Square is what a lot of people call the Old Market Square in Nottingham. It's changed a bit since I moved north. This water feature has appeared. I was fascinated by the waves on the surface and spent some time trying to figure out how it works. Given the waterfall at one end, there must be some movement of water along its length, although of course you'd think that the SURFACE of the water can't slope downwards. This would account for the waves I saw across the width of the feature. But I couldn't see where the water was coming up onto the table. It is deeper in the middle than at the sides. I was pleased with the pigeons because they acted as sources of circular ripples that spread outwards like the ones on the ripple tank in the lab. So can a water surface slope downwards? What about my mountain streams? I will have to think about it.

Leslie's cube and why my physics teacher was wrong

Leslie's tube is a metal cube with sides painted different colours. The idea is to show that the matt black side emits more infra-red that the shiny sides. It's never worked. Now I know why.

Here's the set up with Leslie's tube on the left. The horn in the middle is a thermopile which captures infra-red radiation and turns it into an emf voltage which can be seen on the spot galvanometer. Zero is in the middle on the galvanometer and the spot moves left for a reading.

 

It basically stays in the centre for shiny copper - not much heat radiation given off.

Matt black gives a decent reading.

Shiny white gives at least the same reading!

 

Recent debate on my forum said that any paint is "black at infra-red wavelengths". Now that depends on your definition of black. Black absorbs all visible light, but it is also a good emitter. So if white paint absorbs and emits very well at infra-red, we'd say it was acting like black does with our visible colours. So Leslie's cube will never show exactly what the text books say it should. My physics teacher said we should paint radiators black so they emitted thermal radiation better. He was wrong: white is just as good as black at infra-red wavelengths.

Trams in Slab Square, Nottingham

Nottingham had trams put back in during the last 15 years. You can argue that they reduce pollution in the city centre. But you can't say that electric trams cause no pollution. At the moment the electricity is mostly generated by the burning of fossil fuels. This means that pollution is released in other places. Disadvantages of trams are that they are fixed to going where the rails are. There is no flexibility. Cyclists have to be careful on the rails. Cars share the same routes. And you can see the overhead infra-structure that has to be put in. They ripped the trams out after the war. Will they be a success this time?

A metal kettle

This metal kettle is made shiny silver because it is a poor emitter of infra-red heat radiation. The metal walls would conduct electricity so they are earthed in case the live wire dislodges and touches the case. If that happens, the low resistance route produces such a high current that it blows the fuse and switches it off.

A moment on a mountain bike

My friend's bike has a very precise tightening instruction on the saddle. It says 5.5 Nm. Nm neans Newtonmetres, the unit for turning force. I usually teach it as moments but it is called torque. He even has a mini torque wrench that tightens it to that exactly and no further, It equates to roughly a full jar of jam held at arm's length - the turning effect it would have on your arm.

Reflections in Wastwater

Still water makes a good mirror. Angle of incidence = angle of reflection. The angles are measured to the normal line, which is an imaginary line that sticks out at 90 degrees to the surface of the water. Sadly, it wasn't visible...

Ruben's tube

I saw this on a tour of Lancaster University Physics labs last year. Gas is fed into a tube with a series of holes along the top. The gas escaping from the holes is lit. There is a loudspeaker at one end of the tube and music is played into the speaker. Sound is a series of pressure waves - compressions where the pressure is higher and rarefactions where the pressure is lower. So where the sound wave is at higher pressure the flame is taller because more gas is forced out. Rarefactions produce shorter waves. So the flames go up and down in time to the music. I want one!

Gentle steps for forward progress on Scafell

We walk slowly and place our feet carefully. I was bemused watching some people trying to get up the eroded scree path at speed. They slide quite a long way backwards on each step. The faster you try to walk, the bigger the impact speed on the ground. This means you foot has more momentum when it hits the ground. The rate of change of momentum is bigger. Newton's Second Law says that force is equal to rate of change of momentum, so your foot puts a bigger force on the ground. A bigger force on loose scree pushes it backwards. Newton's Third Law says that if Object A applies a forward force on Object B, then an equal backwards force acts on Object A. So you slide backwards. Crafty physicists tip-toe up and put a smaller force onto the scree. It doesn't slide backwards.

Sea breeze at Allonby

I was at Allonby on a hot afternoon. Look at the flags. They are blowing away from the sea. The wind always comes off the sea and onto the land on a hot day. The land has a lower specific heat capacity than the sea. It is also duller. It absorbs more infra-red heat radiation and the same heat energy gets it to reach a higher temperature sooner. Thus the air above the land reaches a higher temperature than the air above the sea. Air above the land expands, becomes less dense and floats up. It cools at height, shrinks, becomes more dense and sinks over the sea. At ground level it completes the loop by moving back in from the sea to the land. The on-shore breeze is part of a convection cycle.

Make an observation #2

Here's a view on the A6 at Shap summit. Make an observation or ask a sensible question about something to do with Physics.

Paraglider thermals on Scafell

We spotted these paragliders whilst climbing Scafell. The highest of them must have reached over 1000m above sea level. The sun was hot and the infra-red radiation is absorbed by the ground. This heats the air that is in contact with the ground. This air expands and becomes less dense. Being less dense, it floats upwards. It is this upward current of warm, less dense air that is called a thermal. The paraglider spirals to stay in that column of air and is taken up and up. I'm not sure how wide the column would be. However, the force must be enough to lift the person and the parachute.

 

Make an observation #1

Look at this picture carefully. Either make an observation of something that you notice that might be explained by Physics (you don't have to explain it) or ask a question that is to do with Physics based on an observation.

Lower Sixth Challenge Question #1

There is a chain walk along the bottom of the cliffs at Elie in Fife, near St Andrews. They have hung chains over cliffs so that you can hang off them to climb up and down. The safety information says that the bolts from which the chains hang are tested every year to loads of 5kN. Let's assume that the chains are made of stainless steel which has a density of around 8000kg for every cubic metre of volume. Look at the chain in the top picture. How close am I to the safety limit if I hang off the chain?

Preparing for Lower Sixth Physics #19: Precision

The sign says 7 3/4 miles to Sebergham. Ah, fractions! We don't usually use them in Physics. We like decimals because a decimal will tell you the PRECISION of the measurement. Let's go with 7 3/4 metres because it breaks down more easily than it would in miles. 7.75 m would mean it was measured to the nearest centimetre. 7.750 m might seem the same but it actually shows that I measured to the nearest millimetre, which is clearly more precise. So please start using decimal fractions to show the correct precision of any measurement.

Altimeter calibration on Whiteless Pike

After the systematic error when we went to the Secret Cave, this time we remembered to adjust the altimeter in the car park in Buttermere before we set off. The car park was close to the 110m contour. Then we climbed Whiteless Pike, which is 660m tall. The altimeter said 650m on the top, which is not bad. Looking at the map now, I suspect we misread the start height and were out by about 10m before we set off. Bad calibration leads to systematic error later on.