Solar power: another trip to Leighton Moss RSPB

Every time I go the RSPB nature reserve at Leighton Moss I photograph this display. It's helpful in understanding solar power in these latitudes. Here's the previous post from June last year http://wigtonphysics.blogspot.co.uk/2014/06/update-on-solar-power.html so in just over 10 months they have generated 1225 kWh. I now understand that the power = 1.71 kW is irrelevant - it wouldn't power much. But connected to the National Grid, we'd all act like little rooftop power stations. You get paid for the electricity that you generate - it's called the feed-in tariff. If that's still at 14p per Unit, they'd have made about £170. Now if there are maybe 30 million rooftops in the UK, you'd get 42GWh of solar energy a year. I'll need to look up how much the UK actually uses.

Capacitance: phone box in Bellingham

In the days before mobile phones, this is what you used when you were out and needed to make a phone call. I found this one on a campsite at Bellingham in Northumberland. One student game was to see how many people you could fit into a phone box after an evening out. Entertainment wasn't as good in those days. I use this idea to explain the charging up of a capacitor. The first person goes in easily. It's harder for the second person because there is already someone in the space. In fact, every successive person makes it even harder to get another one in. It's like that with charge on a capacitor. Every added charge repels incoming charges more and makes it harder to add more. The rate of addition charge slows and eventually comes to a standstill when you can't add anymore. Thus the charging current falls exponentially.

Radiant in Lazonby

We went to Lazonby church with the bell ringers. They have a modern radiant heating system as shown above. This works by sending down infra-red rays. This offers fast directed heat because it travels at the speed of light and is absorbed by the skin. You actually feel the rays. Central heating doesn't make you feel as warm. It is a very good way of reducing damp in a house but isn't as good at making me feel happy! My guess is that the radiant systems don't need to be turned on as early before an event and would be a good choice for a building that isn't used often. Central heating works by convection which is also not so good in a tall building like a church. But I'd like to see the figures to find out if my hunch is right about which might be the most cost-effective.

Swift as a weaver's shuttle

One of the most important advances in the Industrial Revolution was the invention of a mechanical cotton weaving loom. It used to be done by hand. You weave by making one thread go in and out horizontally through vertical threads. The woven horizontal thread then holds the vertical threads together. In the machine, the horizontal thread was attached to a heavy, steel-tipped piece of wood called a flying shuttle.

This was then fired across the loom. You can see the firing lever at the top of the next picture. The flying shuttle can be seen just above the middle of the picture.

The next picture shows the loom. The flying shuttle is fired left to right, the right to left and so on. It passes through the middle of the white cloth.

Now the Physics... I was told that the flying shuttle went across, back and across again in 1 second - that's 3 crossings in 1 second. I was told that it reached a speed of 45 mph. You need to:
1. Turn 45 mph into metres per second.
2. Use suvat to calculate the acceleration of the shuttle - you'll have to estimate the width of the machine.
3. Use the first picture to given a reasoned estimate for the mass of the largest flying shuttle.
4. Calculate the momentum of the shuttle when it hits the end.
5. Newton's Second Law says that force = rate of change of momentum. Calculate the force as the shuttle hits the end.
6. I was told that if the shuttle jumped out of the loom and hit your head, it would kill you. Do these results back that claim?

Final note is that the quotation "Swift as a weaver's shuttle, fleet our years" comes from the Book of Job in the Bible. But I learned it from a Robert Browning poem when I was at school http://www.bartleby.com/337/1235.html It is in line 51.

Flywheel

What's the function of the big fly wheel? Engine cylinders are pushed out by pressure so how do they get themselves back in again? Some of the energy in the drive stroke is used to turn the flywheel. This has angular momentum which has to be conserved so it keeps turning. This then drives the cylinder in a compression stroke. Angular momentum is angular velocity x moment of inertia instead of velocity x mass. Moment of inertia depends on where the mass is. The further the mass is from the centre the harder it is to shift and so the greater the moment of inertia. So the mass of the flywheel is a long way from the centre and the flywheel is made big to increase the moment of inertia. This increases the angular momentum available.

Would there be tides without the Moon?

Sitting at Ravenglass I got a real sense of the movement of the tides. It was New Moon so the Moon and Sun were both pulling together and there was very high spring tide. We say that the Moon causes the tides, so what would happen if the Moon was removed? There would still be tides because of the pull of the Sun. I did some calculations to work out the pull of the Sun on 1kg of water.

The size of the pull of each on 1kg of water is surprisingly low, and the Sun pulls 200x more than the Moon. But I've read that the Moon has double the tidal pull of the Sun. This is because tidal forces are due to difference of pull on either side of the Earth. I still haven't satisfied myself about how this works but with the Moon being so much closer, the width of the Earth has a significantly bigger effect.

I found the Belt of Venus in Wigton

This time I was ready and looked east. Above the house there is a greyish bit that I used to think was cloud in the distance. Above the grey is a faint pinkish band that is called the Belt of Venus.

 Here is the view to the west into the sunset. Notice the New Moon.

 I had read that the effect covers between 10 and 20 degrees above the horizon. First finger to little finger at arm's length is about 15 degrees but note that my camera was too close to my hand to be truly 15 degrees. The angle shown in the picture is bigger than 15 degrees.

This website has a good diagram explaining the grey bit: http://www.atoptics.co.uk/atoptics/earshad.htm The grey bit is actually the shadow of the Earth because the Sun is now below the horizon of the curved Earth. Looking west a sunset seems red because the light travels a long way through the atmosphere. It encounters a lot of dust so the blue is scattered and red light reaches us. The Belt of Venus is when the red light passes us and is back-scattered in our direction.

Looking for the Belt of Venus

I found this article on the Astronomy Picture of the Day website http://apod.nasa.gov/apod/ap100404.html so I've been looking for this effect. I took this picture from Ravenglass campsite. You can see the Sellafield chimneys in the rosy glow behind the tent.

I'm wondering if the pink band with the grey layer below is the Belt of Venus. I had always thought that the grey was just distant cloud. Research tonight suggests I should be able to see the effect in all directions, not just in the direction of the sunset, so I'll look again.

L6 Estimation question: the fountain

 This fountain is on the Kurfurstendam, the main shopping street in Berlin. Use estimates of the height that the water reaches and the distance it travels to help you to calculate the VELOCITY of the water as it is fired from the fountain. Remember that means MAGNITUDE and DIRECTION.
Just so you know where you are, I then turned round to take this picture of the Kaiser-Wilhelm-Gedaechtnis-Kirche...

La'al ratty: the power of steam

We visited the Ravenglass and Eskdale Railway. We were amazed to see the big load being pulled by such a small engine. I counted 10 carriages. You could fit 20 people on each. Say an adult was 60kg. 20x60x10 = 24000kg. Now say eaxh carriage had a mass of 1 tonne - there's another 10000kg. I timed the train as it accelerated out of the station. I estimated 25 metres in 45 seconds, by counting carriage lengths. Using the suvat equations of uniformly accelerated motion, I got an acceleration of 0.025 metres per second per second. Using Newton's 2nd Law equation F=ma gives a force of about 550N. My weight is not much more than this. The problem is that I've discounted friction. The implication would be that if you hung me over a void on a rope over a pulley, I'd get the train moving. That wouldn't happen because of the friction. Also, the acceleration was probably bigger - I think the train had reached a steady speed well before the 25 metres was up. Finally, the carriages might be more than 1 tonne each.

U6 Estimation question: Melting a block of ice

 I put the block of ice on a wall when we went out for a walk. When I came back later it had all melted. Calculate the amount of energy needed to melt the ice if the starting temperature in the morning was -5 degrees Celsius. (The meltwater trickled away as shown in the picture above, so you can ignore any heating of the liquid water.)

Old-fashioned toilet flush

I've wrestled with this type of flush in the past but now I know how it works. The display board shows that the central pipe is double-headed inside the flush mechanism. One side is attached to a sealed section with a plunger in. Pulling the chain pulls the plunger up and drops water into the pipe. The rush of water past the open end of the other side of the pipe reduces the air pressure. I think this might be Bernoulli's Principle but it's been a long time! Thus higher pressure air above is able to push the rest of the water up and over. There's now nothing to stop the plunger sinking back. The ball cock has dropped in the meantime, opening the tap and letting water flow in again.

Steam engine governor

The two balls in the middle of this photograph are a steam engine governor. I've known about them for years but hadn't realised they were such a big deal. Apparently they were a James Watt innovation because his rotary steam engines had to be kept at a constant speed. The engine spins the ball mechanism as well as driving its load. If it goes too fast, the balls gain energy and move outwards. This pulls on the levers at the top of the ball mechanism which reduces the size of the fuel inlet. Less fuel in means the engine slows down. The balls spin slower and gravity pulls the balls down. The levers open the hole and more fuel goes through... I was amazed to find that the maths of it was done by James Clerk Maxwell and that Gibbs based his thermodynamic analysis on it. http://en.wikipedia.org/wiki/Governor_(device)

Electromagnetic fuse

I found this in the Technical Museum in Berlin. It turns out that it is an anti-aircraft rocket. Rockets work by Newton's 3rd Law. The fuel burns and the rocket pushes the hot gases out behind it. But the gases push forward on the rocket, which makes it go forwards. I was interested that it claims to have an elektromagnetischer Annaherungszunder - an electromagnetic approach fuse. In English, it's a proximity fuse. http://en.wikipedia.org/wiki/Proximity_fuze Apparently the nose of the missile was electrically insulated so it could store static charge. Then the metal in the target plane would act as the other side of a capacitor. Capacitance would change. I'll have a think about what this would do to the stored charge...

Reflecting on the Reichstag

 The government buildings next to the Reichstag in Berlin showed nicely the way that glass can both transmit and reflect light. I think the idea of the glass wall is to show the transparency of the democratic process. Articles of the constitution are written on the glass. It's very effective. In the first picture I am almost looking down the normal line. You can easily see the light transmitted from the building inside but the reflection is not very significant. Below, the angle to the glass is more acute so the angle of incidence, measured to the normal line, is much bigger.

 Below is almost total internal reflection. TIR is less effective in the foreground because the angle of incidence is much smaller. This is not the sort of example that you find in a text book because across this long surface there are many different rays at many different angles. Most of them are higher than the critical angle.

 And finally there was the Moon reflecting the light of the Sun...

It used to be called a cigarette lighter

We sadly said goodbye to our old car, which was older than some of my students. And it had a cigarette lighter. These days you call it a 12V socket, apparently. I'd never used the cigarette lighter but in the interests of Physics... You push it in to connect the circuit. There is a spiral of resistance wire inside which gets red hot due to the current flowing through it, hot enough to light a cigarette. Then the lighter pops back out of the socket. My speculation is that the metal expands as it heats up and loosens the spring's grip, letting the lighter pop back up. I'll need to check that, though.

Way out West

I've been reading the i newspaper this week. This feature appears on the weather page. It shows the hours between sunset and sunrise. We went through the spring equinox about 3 weeks ago so the north should now be ahead of the south for hours of daylight. I looked at Stornoway as the most northerly listed and thought that it looked to be too far ahead. Then I realised that it is also the most westerly. They are all measured against London time, but sunset will be later the further west you go because London is in the east. So I compared London with Hull. They are both the same distance east. Hull gains 4 minutes by being north. Compare Swansea, Bristol and London. They are the same distance north. Swansea is 6 minutes west of Bristol and 15 minutes west of London. But Swansea and Inverness are the same distance west. The north of Scotland is already 10 minutes lighter at night than the south of the UK.

New pylon type to look out for

The National Grid is getting new pylons. This article has some interesting details http://www.bbc.co.uk/news/uk-32225276

More sun dog days in Wensleydale

Sun dogs were visible twice more on the same day. I've never known a day like it! So I got to test the idea of measuring the angle. The distance between thumb and little finger in the top picture is said to be about 25 degrees. The top half of the full circle also appeared, I tried to photograph the whole thing but it subtends more than 45 degrees, It looks like the field of view of the camera is about 30 degrees. I'd never thought about that before, The bottom picture shows the right hand sun dog as well.

Sun dog in Wensleydale

I've posted about sun dogs before and here's another one. It's in the top picture, to the left of the Sun. They are caused by refraction - that's a reasonable guess given the splitting into colours. It's about hexagonal ice crystals in the high cirrostratus cloud - that's cirrus done as a thin layer. It's 22 degrees from the Sun to the sun dog. Outstretched arm with thumb and little finger deployed is 25 degrees. It's about right for a rough measurement. There's supposed to be another one on the opposite side of the Sun. The cloud was a bit thicker there but I convinced myself I could see something...

The Great Bear in Berlin

A bear is the symbol for the city of Berlin,.You find it on the city flag. I have read that it because they say "Bear-lin" not "Burr-lin" as we do in England. There are a lot of these beautifully painted bears in the city. I liked this one most of all, Constellations are a funny thing. They are all in the human imagination. The stars in each constellation are all different distances away but are seen by us in the same direction. But they are a useful way of finding your way round the sky. The constellations of the zodiac are given prominence on this bear. They are the constellations that are on the same plane as the Earth, the Sun and the planets. That's why the planets seem to move through these constellations. The solar planets don't appear anywhere else in the sky.

Waveguide: back in the Stasi Jail at Hohenschonhausen

I find the Stasi Jail affects me a lot because so much of it still stands and because of the way individuals were isolated for long periods of time. One of ways of attempted communication involved the toilet. The idea was to disable the flush so that the bowl did not refill with water. If there was no water in the pipes, then the pipes would act as a primitive sort of wave guide for sound waves and allow conversation. Water does transmit sound: you can hear underwater. However, I think that the dissipative viscous forces in the water would attenuate the sound. So you'd get clearer communication with no water there. The problem was that just as with social media, you couldn't be sure that the person on the other end was who they said they were. Our guide said he was arrested in 1984 at the age of 18 for trying to escape from the DDR. I was 18 in 1984... 

Telling the time in Alexanderplatz

I've been back in Berlin on another fantastic trip. I noticed some new things this year, like this clock in Alexanderplatz. Sadly, I only got a good look at it on the last night. I think that the numbers in the middle rotate. It was almost 9pm in Berlin so I suspect the bottom picture shows it about to flick round. But it was a useful way of explaining the way that 12noon is only a number given to the time when the Sun is highest in the sky where you are. We were further east than London so that happened an hour or so earlier. Rather than have each place have its own perfect adjustment (eg Wigton is really about 10 minutes behind London) we divide the world into 24 strips and within that strip they are all supposed to have the same time. An approximation to the Physics but more practical.