Neon in a sodium street lamp

 

It finally occurred to me to ask "why do sodium street lamps start out red before they warm up to orange?" Turns out that the tube is filled with a mainly neon gas mixture which lights up immediately and glows red before the sodium is fully vaporised. This article is brilliant. There's a lot more there to think about.

Big Crush not the Big Crunch at Green Side

 We visited one of the two huge craters on Green Side next to Sheffield Pike. It turns out that they are not quarries but are the result of a massive underground collapse in 1862. W T Shaw's Mining in the Lake Counties implies that it was due to miners taking lead out of two parallel vertical veins that left a plug of rock suspended. It duly collapsed one Sunday, so no one was hurt. https://en.wikipedia.org/wiki/Greenside_Mine has more details and an excellent photograph. The event was called the Big Crush. I spent the day thinking it was the Big Crunch. When I started teaching, it was expected that there was enough mass in the Universe to make slow and eventually reverse the expansion of the Big Bang, resulting in the Big Crunch . The 1999 evidence from Type 1a supernovae shows that the Universe is undergoing accelerated expansion so the Big Crunch is not going to happen.

Another 2 metres

 

This was in Ambleside a couple of months ago. If resolution = +-half scale division at each end, then total uncertainty in the social distance = +-1sheep.

Lost in Math by Sabine Hossenfelder

 

I read the book above. The central thesis is that experiments cost so much to build and take so many years to construct, that most ideas will not be able to hope for experimental verification. So what do we do then? Also, how do we choose which ideas to test when the funds are available? Sabine Hossenfelder suggests that what has happened is a retreat into mathematical aesthetics. Does the theory look simple and elegant? If so, it must be true. I think she's right to point out that the real world might not have to be simple and elegant. 

Red sky in the morning

 

I was brought up on caravanning holidays with the weather-predicting rhyme "Red sky at night; shepherd's delight. Red sky in the morning; shepherd's warning". I was amazed when I started teaching that none of my classes knew it. This morning the eastern sky was red. It is very stormy now. I understood that it works because frontal systems pass from west to east and take several hours to pass. I looked this morning and did a double take, because surely the clouds lit up red are those in the east. Recourse to this suggests it is because the air in the east is the stiller air that has more scattering dust trapped but that stormier air is coming from the west. This needs pursuing. However I was amazed to find that I had never noticed Jesus quoting the saying in Matthew Chapter 16. This means that the saying is at least 2000 years old and it still works.

Yan, tyan, tethera - counting systems above Ullswater

 

We found three stones celebrating the local counting system for sheep https://en.wikipedia.org/wiki/Yan_Tan_Tethera I have been aware of it but haven't thought about it much. I hadn't been aware that it was base-20. Then I remembered that Gaelic has a counting system based on fichead, which is twenty. Base-20 turns out to be called Vigesimal . There are many examples and it does turn up in English in the word "score" as in "three score years and ten". 

Inverse square law for gamma

 

It was only in recent years that I learned the trick of putting a Geiger-Muller tube vertically for gamma, which can go through the metal sides. It eliminates alpha and beta. It is also supposed to make the distance measurement more accurate because of the circular symmetry. It is not possible to know exactly where in the tube the gamma is detected but they say this makes the distance measurement better because you measure to the middle of the tube. Sitting the gamma source firing downwards into lead also works because the reduced radiation leaking sideways out of the casing means more than one group can use the same source. The disadvantage is that the range is reduced. You'll see that I've had to set the distances at 5mm intervals which is much less than the diameter of the tubes. Nevertheless the results do work.

Automatic cut off on a kettle

 

The lab kettle has a cracked lid and is taking a longer time to turn itself off. I know that the electrical cut off is to do with steam so after the pan boiling adventure this month I wondered if it was to do with the pressure of the steam being reduced by the crack. It turns out that it is to do with steam, but that it is a temperature thing. The steam travels down a pipe to flip a bimetallic strip in the base which then turns off the power. It is explained properly here . In this case, steam escaping through the crack means that less is directed down the pipe so it takes longer to reach the required temperature.

Fisher's Wife's Rake: at an angle on an inclined plane

This is Fisher's Wife's Rake on Clough Head. Apparently Mr Fisher cut peat above and it was his wife's job to get it back to the farm on sleds down this wickedly sloping narrow path. The start (above), which is beyond the famous tree, is clear enough but then we had to keep to the left along the line of the crags to stay on the path.

The path itself goes up at a steep angle but it also cuts across an inclined plane. I wondered how the geometry affected the actual slope climbed. I find that the steepest slope for walkers to be OK is about 45 degrees so I've modelled it at a 30 degree slope.

First of all I drew a 100m line going up a 30 degree slope across a vertical face. I've said it is 100m above the ground. The height gain from A to B would be 100sin(30) = 50 metres. The slope is said to be 1 in 2 (or 50%) because you go up 1 metre for every 2 metres along the path.

Then I took the diagram and tilted it over to an angle of 30 degrees to mimic the situation on Fisher's Wife's Rake. Now A would be 50 metres above the ground and B would be 75 metres, so by walking 100 metres you would end up 25 metres higher. That's a slope of 1 in 4 or 25%. By angling across a plane, the gradient can be reduced.

 

Westminster Electric Motor Kit

 

This model electric motor is called a Westminster Motor Kit. The key to getting it to work is making sure the contacts (shown circled in green in the diagram) are correct. The horizontal wire is taped to the rotor axle with red tape. A vertical wire pokes up through the base. The are not joined but just touching. They must rub against each other as the rotor spins. There is one on each side. I have always favoured holding them between finger and  thumb as shown below so that correct pressure is applied. You usually have to feel which way it is trying to spin and then give a push. The extra momentum given is enough to get it round to the far side and remake contact.

The picture above shows current entering the coil top left and slowing downwards on side A. It goes round the end and flows upwards on side B, leaving the coil top right. Even when the coil has flipped over 180 degrees on the axle, it must still be going down at A and up at B. Hence the sliding contacts. The sliding contacts are called a COMMUTATOR. The magnetic field is shown in green. By Fleming's Left Hand Rule, side A comes up and side B goes down. The connection to the battery is shown below.

The Physics of a Compost Bin

 

This is my friend's super compost bin. Look at the thickness of the insulation. EPP or expanded polypropene has a themal conductivity of 0.035W/mK. As you'll see below, the temperature in the actual compost itself was about 70 degrees Celsius and a little lower in the trapped air space above. That would give a temperature difference in excess of 50 degrees at the moment. The thickness of the insulation is about 4cm. This means that 0.07Joules per second get through the insulation. Then I went searching for a U-value. I couldn't find one but I did find that U-value = thermal conductivity/thickness = 0.035/0.04 = 0.875 W/m^2.K So by finding the surface area we can calculate the rate of energy loss of the whole compost bin. 

Rate of loss of energy = surface area x U-value x temperature difference = 2 x 0.875 x 50 = 88Watts. That's not far off what is given off by a resting adult human. 

The micro-organisms responsible for the decomposition release energy by respiration, which is an exothermic reaction. 

Space-saving solar panels at Saltholme

 

I spotted these solar panels at RSPB Saltholme a couple of months ago. They show an interesting way of putting up solar panels whilst not using up too much space. I'm also interested that they are angled in together. Arrays normally tilt the same way, angled towards the Sun.

Looking at AC interference

 I pointed the search coil at the back of a plug.

The pattern on the oscilloscope clearly showed that it was picking up a signal from the AC magnetic field. But the induced emf is very small, of the order of 0.01V.

The fluctuation on the signal is also interested. The time base is 5 microseconds per division so the frequency of the large scale oscillation is 100000Hz. Need to look at this again.

Tungsten mine in Mosedale: high melting point

 

There's a display board appeared at the mine in Mosedale since I last visited. Tungsten used to be a well-known element because it was used for the filaments in light bulbs. This was because the melting point was so high. That leads me to ask the obvious question: why does tungsten have such a high melting point? I don't know enough about solid state physics to really understand this but I am interested that increased shielding increases the melting point. I do teach that more shielding means more reactive because the nucleus is less likely to hold onto outer electrons and thus lose them to form positive ions. But here maybe it is the losing of electrons that leads to more metallic bonding. Maybe all will become clear with more solid state knowledge. 

Is this a counterweight?

                                   

I was watching this tractor placing a new caravan. There was a large box on the front shown as A. I was wondering whether this was heavy to produce an opposite moment to that given by the caravan and stop the tractor's front wheels being pulled up into the air as it pivots on the back wheels. I'm not convinced because normally the engine is heavy enough on a road car to do this for a touring caravan. Since most of the weight of the van is supported by the wheels, the downward force at the towing point shouldn't be large. That would mean that the tractor won't be supporting much weight, just providing a forward force to get the caravan moving.

Triple glazing as sound insulation

 

No wonder it was so hot in the hotel room. It turned that as well as the traditional double glazing there was an inner sliding pane. Since the hotel was on the motorway, it must really have been about sound insulation. At the risk of seeming to promote a commercial interest, I did a search and this was one of the first to come up. It suggests that at least 100mm air gap is needed. Well, that would be the gap to the secondary glazing here. It also suggests that panes of different mass would be best. I'd need to look another time. However I've also found a paper on the topic to go away and read which might give an academic account.

The raindrop explodes

 The raindrops were hitting the roof of the car so hard in the summer that it was possible to see them bouncing up again. I was wondering how to analyse this. Normally when an object bounces back from a surface I use conservation of momentum. Here it is definitely not going to be an elastic collision. Some of the kinetic energy will be dissipated as sound. I looked up the terminal velocity of a falling raindrop. These were large drops - about the size of a house fly - so this source suggests 10 m/s. A spherical drop of 6mm diameter would have a volume of 0.11cm^3 and thus a mass of 0.11 grams. This would give a kinetic energy of 0.0055J. Suppose the whole drop bounces back up 2cm, an assumption, then the drop would have been given kinetic energy=mgh after the impact =0.00002J. In other words, most of the kinetic energy on impact is dissipated. It is obvious that the linear momentum of the drop is not conserved. So to justify conservation of linear momentum, the roof of the car must move slightly, thus producing the sound.

Natural panpipes on Lonscale Fell

 

The wind was blowing across two open ended gate suspensions on Lonscale Fell. This produced two different tones which blew alternately as the wind gusted. Suppose B was about 120cm long. Given a stationary wave with antinodes at each end and a node in the middle, the wavelength is 2.40m. This gives frequency = speed of sound/wavelength = 340/2.4 = 140Hz to 2sf. That is low but audible. The broken shorter pipe is about 50cm long giving a higher tone of 340Hz.

Social distance with ants

 The 2 metre social distance has inspired a whole genre of new units of measurement.

Here at Abberton Reservoir it was ants. That means that an ant is 2000mm/400=5mm long. A little research shows that is about right. https://en.wikipedia.org/wiki/Black_garden_ant I've never measured any myself.

Inverse square law at Lingy Hut

 The window in Lingy Hut reminded me of the grid that I use to demonstrate the inverse square law for light to my classes. Shine a light so that it covers one square then move twice as far away and show that it covers all four squares meaning the same energy has spread over 4x the area and that if you double the distance then the intensity will quarter.

So I took the photo above from the middle of the room and the one below from the far wall. The area above is 3.1 x the area below so it has not quite worked but the distances were guessed.

A pan boils over

 I was cooking pasta. It is more efficient to boil with the lid on. However even with a steam hole in the lid and on the lowest heat, the water would bubble up and boil over.

Lifting the lid, a visible burst of water vapour was released upwards.

And the liquid settled down.

Here's what I think is happening: Normally as water boils, steam forms in bubbles inside the liquid. The pressure in the bubbles is higher than that in the surrounding air so when the bubbles reach the surface, the pop and release water vapour into the air. With the lid on, the water vapour can't go anywhere, so adding extra particles. It is also hotter so the particles move faster and are at a higher pressure. This means that bubbles of steam reaching the surface do not pop as easily because the pressure outside is now equal to the pressure inside. Hence it bubbles up. Lifting the lid releases the pressure because particles depart. The bubbles pop and water vapour is released.

Mersea pulpit

 

The pulpit in the church at East Mersea had a roof over it. I guessed correctly that this acts as a sounding board to reflect sound towards the congregation. In the days before electric amplification it would be difficult to hear a preacher in a large church so any help in directing the sound towards the congregation rather than upwards into the roof space was a good thing.

Infra-red heater produces optical corona in St Edmund's, East Mersea

 

The parish church at East Mersea was wonderfully welcoming. The infra-red heaters produced a different type of optical corona through the steamed-up glasses than white lights. As expected, it was dominated by red wavelengths. Water vapour is an absorber of infra-red that then reradiates in all directions in the atmosphere. It would be interesting to try to see what such steaming up might do with an infra-red detector.