Convection on the morning before All Saints

It's All Saints day tomorrow. I've never made a pumpkin. When I was little, they hadn't arrived over here. We did apple bobbing. Mrs B gave me some pumpkin seeds and this is what grew. Looks like a marrow but we craved them anyway. I did the big one and Mrs B did the little one. We had to cut a slot into the lid of the little one. A burning candle needs oxygen. Getting fresh oxygen in needs convection. The hot air rising from the flame has to go somewhere. And its departure leaves a lower pressure space that pulls in air from the surroundings. The hot air needs to leave from the top; the cold air comes in at the bottom. My pumpkin was big enough for the facial features to service both needs. In the smaller pumpkin, the features were so low that the hot air could not escape and thus no cold air was pulled in.

L6 link to Searle's Apparatus Young's Modulus film

The link to the film of the experiment is https://www.youtube.com/watch?v=2UMUqsINvxU . It's a great film but note 1. Health and Safety issue at 3 min 45 seconds 2. You would need to explain how to get Young's Modulus from the graph she describes.

It was Young's Modulus when I was at school. It seems to have become the Young Modulus now. I'm guessing because it is named in honour of Thomas Young but that he didn't invent it, hence the change.

Get knotted - learning to knit

 I've been learning to knit. It is a clever technology for making knots. I posted about knot theory at the end of July. Pictures of knots are called graphs in maths. They don't mean the same as graphs in science lessons. They mean network diagrams. Such network diagrams are useful analytical tools.

 My best attempt to model the knots made by the moves shown above comes out like this. I think this is likely to be a looped trefoil knot. It may not even be a knot properly because it can be pulled out.
                                    

Sloe gin and a random walk

I've been making sloe gin. You dissolve a large amount of sugar in half a bottle of gin and add sloes. Here it is after the first night. Look at how the red colouring has started to diffuse up the tube. Diffusion is the movement of particles from where they are most concentrated to where they are least concentrated down the concentration gradient. It works because of the random motion of the particles. In fact, they can be modelled using a dice with each number suggesting one of six directions. For each single molecule, the resultant path is called a random walk - or the walk of a drunk, perhaps after consuming too much sloe gin. But if you have millions of particles close together, the overall effect of these individual random walks is a spreading of the colour. I'm now at the stage of shaking the bottle every couple of days which spoils the effect but will give me a nice drink at Christmas!

Copper bottomed at a bothy

We visited a remote bothy in Scotland. Mrs B spotted a pan that someone was using - a Physics teacher's favourite. I've taught about them often and said copper is a better heat conductor than steel but more expensive so the sides are steel and the bottom is copper. Turns out it's more complicated than that. Apparently it's about spreading the heat evenly. I suppose that with metals that don't conduct as well, if you heat with gas only the bit directly above the flame will conduct through and so the food in that place will be heated more. But with copper, there will be better lateral conduction so food above other bits will get heated. It is also said to be more responsive to changes in heat. They also say that copper reacts with acidic food and the results can be poisonous. So a stainless steel lining stops that happening.

Poppies:Wave at Yorkshire Sculpture Park

The poppies installation at the Tower of London last year caught the public imagination. Part of it has come north. As a physicist, the title "Wave" grabbed me. Looking at it, I read it as a breaking wave that has come down the lake and is about to crash into the bridge. Water waves are not truly transverse. They form from a circular motion in the water. When the wave motion reaches shallow water, the full circle cannot be completed and the wave breaks. The symbolism is quite dramatic: the poppies reach up to my level. I am not immune on the bridge, above the storm. The breaking wave reaches me.

No front or back at Yorkshire Sculpture Park

We spent an afternoon at the Yorkshire Sculpture Park. You should go! I liked this piece, called Shogun by Phillip King. As is often the case, it was the thinking behind it that pulled me in and got me thinking of Physics. He says that he has created no privileged viewpoint: it has no front or back. I was thinking that this is not unusual in Physics. It is unusual for there to be a particular direction in Physics, as with time only having one direction. However, I'd say that in Physics, having no privileged direction usually means symmetrical. This is not symmetrical at all.

Fields around Holmfirth

I took this picture above Holmfirth in Yorkshire. The fields got me thinking: who was the first to use the word "fields" with reference to force in Physics? It turns out that it was Michael Faraday in 1849. He is famous as the man who used iron filings to see the magnetism extending into the space around a magnet. I do that experiment a lot. Perhaps it was something about the extent of the iron filings on a flat surface. Michael Faraday's father might have recognised this landscape, having moved his family to London from the Pennines, but Michael himself was born just after the move. I wonder where Michael Faraday got his inspiration for the term?

Force multiplier gate on the Threave Estate

The pivot for this gate bolt is at the bottom. The point of action is close to the pivot - the bit that pulls the bolt back. I pulled the handle at the top. Pivot to top is FIVE TIMES the distance from pivot to bolt. Yet each must be experiencing the same turning force, the same MOMENT. Moment = force x perpendicular distance. If the distance is five times bigger, the force will be five times smaller. Put another way, whatever force I put at the top will be five times bigger at the bolt. This is a FORCE MULTIPLIER.

Thirlmere Dam

Shasowing the Duke of Edinburgh Silver hike took us over the Thirlmere Dam. It is said to have raised the water 20 metres above the old stream level. I have read about the Thirlmere Aqueduct. It heads south for nearly 100 miles to Manchester with the water flowing only under gravity. It is never pumped. The dam is 190m above sea level. I'm not sure how high Manchester is above sea level, but the water is going down less than 2 metres every mile. It's going to be about 1 metre down every 1000 metres or 1mm every metre. Put like that, it doesn't sound much!

Quarks: chocolate muffins, Finnegan's Wake and Aspatria

Mrs B found a recipe for chocolate muffins. It came from the Lake District Creamery at Aspatria, just down the road. This sort of quark is a "fresh acid-set cheese" used a lot in Central Europe. In Physics, a quark is a sub-atomic particle that makes up HADRONS, the particles that feel the strong force. A proton and a neutron are each made up of 3 quarks. Apparently the name comes from the book Finnegan's Wake by James Joyce. This is allegedly the hardest book in the English language to read. Murray Gell-Mann, who came up with the theory, is said to have noticed a line in the book: "Three quarks for Muster Mark" when beer was being ordered at the bar. Three quarks were in the protons and hence the name. It's a wonderful story. I tried reading the book. I knew the plot outline but 200 pages in and I hadn't discovered a shred of the story! It's poetic and sounds nice if you read it out loud. And the chocolate muffins tasted amazing!

Year 10 copper mines question

This is Coppermines Valley at Coniston. These spoil heaps you can see are rocks that used to be underground.
1. Estimate the volume of the rock, giving reasons for you answer.
2. Let's say that 1 cubic metre of rock has a mass of 2.5kg. Calculate the mass of rock in these spoil heaps in kg.
3. Suppose that the rock was dug up from 100 metres underground and hauled up. (Perhaps not unreasonable after consulting http://www.cumbria-industries.org.uk/a-z-of-industries/copper/) Calculate the gravitational energy gained by the rocks using a formula mass x g x height. g is called the gravitational field strength and is 10N/kg on Earth.
4. Suppose that the energy to lift the rocks (ie to give them the energy you just calculated) came from petrol generators. Generators are probably about 30% efficient, which means that only 30% of their energy woild go to lifting the rocks. The rest is wasted as heat and sound. So calculate the petrol energy needed to cover lifting the rocks and all the wasted energy.
5. Petrol has an energy density of 32.4 kg per litre. Calculate the number of litres of petrol needed.
6. Calculate the cost of all of that petrol.
7. Find out the price per kg of copper at the moment and calculate the mass of copper you'd need to dig up to make it worth shifting all of those rocks. Could this mine be economic?

Sixth Form estimation question 2015 #2

Yesterday was a great day for viewing planes. I timed how long it took the plane to go from my little finger to my thumb - 22 seconds. My little finger is worth 1 degree. Compare the plane to my little finger to work out how many degrees the plane is worth. Then use a triangle method to work out how high up the plane is. Then work out how many miles the plane actually flies from my little finger to my thumb and calculate the speed of the plane. Comment on whether the speed is sensible.

Testing the waters on High Pike

 When we came down off High Pike this afternoon, we found a mine pool with water that looked unnaturally blue. Perhaps it might contain copper ions because copper sulfate is blue. Mrs B bravely got me a sample. We set up an electrolysis experiment at home using nails as electrodes.

 Initially there were bubbles of gas appearing round the negative electrode. No copper ions appeared as hoped. I suspect they were bubbles of hydrogen and that we were merely separating water by electrolysis. There was a small current of 2.3mA. I was using a 9V battery.

 This is what happened when it was left for over an hour. I think that what has happened is that iron ions have been pulled into the solution from the positive electrode and that this is what has given the distinctive colour to the solution. The current peaked at 4.0mA which suggest that the extra ions had improved the conductivity. There is as yet no clear evidence of fresh iron being deposited on the cathode. If that happened, then this experiment would be like the one we tried in class where we used electrolysis to purify smelted copper.

Red shift with a bit of a balloon

 I drew a wave onto a bit of balloon.

I stretched out the balloon. The wavelength is now longer. Not rocket science, I know, but this is the RED SHIFT. Look at the wavelength pictures on this NASA website http://science.hq.nasa.gov/kids/imagers/ems/visible.html Red has the longest wavelength and violet has the shortest wavelength. The Universe is expanding. In other words, the very space between galaxies is stretching. This means that light waves are being stretched. Stretched light has a longer wavelength and is nearer to being the red wavelength. So we say the light has been red shifted. The space between the galaxies is stretching, so the galaxies end up further apart. Now put it the other way round. Edwin Hubble spotted that every galaxy had a red shift. He knew that could only be happening because the wavelength was being stretched so he concluded that space was stretching and the Universe was expanding. The final bit of logic is to run this imaginary film backwards. If it is expanding at the moment, run backwards it would get smaller and smaller until it took up no space at all. The moment at which the Universe took up no space at all is called the Big Bang.

Reactivity of metals and displacement reactions

We did an experiment with blue copper sulfate solution. On the left, we added iron, the middle was zinc and the right was magnesium. Notice that for the two on the right, the solution is no longer blue. It is no longer copper sulfate. On the right, the magnesium metal is more reactive than the copper, so the copper and the magnesium swap places.

Magnesium sulfate has no colour. The slightly rusty coloured stuff in the liquid is actually the displaced copper. It has been dumped out of the liquid.
The same applies in the middle reaction. Zinc sulfate is colourless and you can see the rusty coloured displaced copper.

There is some physics behind the reactivities that is usually taught with metals by how easily they can get rid of electrons to form complete electron shells. This becomes more difficult when you get to zinc and iron which are Transition Metals on the Periodic Table. I'm working on an explanation that satisfies my own curiosity. I found this lovely blog post whilst looking. It works at our level and shows the experiments really well. I'm going to have a go at the very slow reactions! https://chemlegin.wordpress.com/2014/08/31/unreactive-metals/

100 degrees on Dale Head

Brewing up on Dale Head today I was asked if anyone had ever brewed up on the top of Everest. It is not possible to brew a good cup of tea on Everest. I was taught this at school but such things have gone out of fashion in teaching because there is so much else that now needs including. Water boils when the molecules have enough kinetic energy and therefore momentum to overcome surface tension and the push of the air molecules above. At sea level, we call that 100 degrees Celsius. At high altitude, the air pressure is much lower so there is less to stop the escape of water molecules. Yes, water boils, because it all changes from liquid to gas, but now the temperature at which it does it is much lower. I think I remember being told 60 degrees Celsius. That's not hot enough for good tea, so I'm told by Mrs B.

U6 Estimation question 2015 #1

Calculate the maximum tension in the support cable. This time, here's an outline of what to do:
1. Use a pendulum formula to calculate the time period. Now you have the frequency.
2. Use one of the SHM formulae to calculate the maximum speed of the swing.
3. Now use the centripetal resultant force to get to the tension.
The swing is at Whinlatter, so next time you go...

To Scale: The Solar System

If you haven't seen this film, set aside 7 minutes of your life! You won't regret it. It made me so happy. https://vimeo.com/139407849 I love the bit when he says: "We are on a marble floating in the middle of nothing."

Measuring a sun dog in Silloth

 I saw this sun dog in Silloth last week. It is the small streak of coloured light above the red dot (I think the red dot will be lens flare) and just by the roof of the house. It appears in real life as a slight rainbow. I wasn't sure this time - it seemed so far from the Sun. Perhaps it was because the Sun was so low. The Moon always seems bigger lower down but it just an optical illusion. So I decided to measure it. It took one hand splayed thumb to little finger and 3 fingers of my other hand held at arm's length. I came home and measured.

Imagine a right angled triangle going out from my eye to my little finger, across to my left hand finger and back to my eye. My fingers were 70cm in front of my eye. Let's call that the hypotenuse. Sin theta = 24cm/70cm. So the angle = 20 degrees. It is 22 degrees for a sun dog due to the optical geometry of light in water crystals high in the atmosphere. So it was a sun dog!

Venus in the daytime

I received a tip off that Venus was visible in broad daylight today. THANK YOU! It is just possible to see the crescent Moon in the picture above. It's somewhere in the middle. Venus appears as maybe one pixel in extreme enlargement. In real life, by squinting, I was able to make out a bright dot in the sky about 3 finger widths at 10 o'clock (ie north-east on a map page). Not easy to pick out until you know where to look. To the naked eye it might seem like a really high aeroplane. As you can see, it didn't photograph well with the better camera so I got out my wildlife telescope and the cheap camera. It turns out that Venus is showing us a phase quite similar to that of the Moon.

Venus's orbit is inside ours so it is possible to see both its lit up and shadow sides. I think Galileo was the first person to notice this.Galileo used this observation to show that Copernicus's model that had the Sun at the centre of the Solar System was correct. There would be no other way of explaining the phases. http://solar-center.stanford.edu/gal-challenge/gquiz6c.html

Listening in: Threave gardens

I found this listening device in the gardens on the Threave Estate at Castle Douglas. It must be for listening to birds in the trees. All I could hear was a continuous low-pitched note. I know that 50Hz is about the lowest frequency we can hear from the signal generator in the lab. So suppose that a stationary wave is set up in the pipe by the wind vibrating the air. We say that since there is nothing to stop the air moving, there must be an anti-node at each end and therefore a node in the middle as shown below:

This means there is only a half wavelength in the pipe (two quarter waves back to back). If the pipe is 3 metres long, the full wavelength would be 6 metres. The wave equation is:

Wave speed = frequency x wavelength

We'll take the speed of sound in air as 330 m/s. So Frequency = 330/6 = 55 Hz. It could be right.

More wake - Catbells this time

I was back to looking at boat wake when we went up Catbells. There were unusual features to the pattern in the bit circled. I looked up the Kelvin wake again - must learn how to do the theory. https://en.wikipedia.org/wiki/Wake It asserts that the angle between the arrow and the red line should be 19.47 degrees. Also, the wavelets I've coloured yellow ought to be at 53 degrees to the arrow. I will try to get photographs from an angle that allow proper measurement.

Radio Frequency Security Tag

A local shop sold me a product yesterday - I have the receipt! - but they forgot to take off the security tag. The alarm didn't go off, though! I wondered if it worked by electromagnetic induction - that ferro-metallic strips inside disrupt a magnetic field created by the detectors at the door. I discounted the idea because any ferrous metals would set off the alarm regardless of whether it's a shop product. Also magnetic fields might interfere with portable computer storage devices. A bit of poking on the Internet found this http://www.explainthatstuff.com/rfid.html The implication is that the doorway detectors are radio frequency transmitters that won't harm anything. But the strips in the tag are aerials to pick up the signals and re-transmit them. The energy must come from the electromagnetic waves themselves. I'm not actually sure that the strips inside looked like aerials. Could it just work by reflection? But if so, we'd be back to the problem of metallic things in customers' pockets setting off the alarm.

Further observations of turbulence in Staveley

I also noticed laminar and turbulent flow on the mill weir at Wilf's cafe in Staveley. The water coming down the duct on the left is quite turbulent but then it emerges onto a wide flagstone. The water in that section is crystal clear suggesting smooth flow over a plate. As it drops over the edge it immediately becomes turbulent. Perhaps the plate forces smooth flow whereas as soon as it drops it can flow anywhere.

Spinning the plate

Mrs B has been hankering after a career in the circus after our trip to Zippo's. We bought the spinning plate there and she mastered it very quickly. I've been hopeless until today! You start with the plate sideways on the tip of the pole as shown in the top picture. It seems that the technique is to have a flexible wrist and wobble it from side to side. I was tending to keep it in one place and try to spin. I think the wobbling will be like trying to balance a pole on one hand. With the pole, you'll never get your hand exactly under the centre of gravity so you move it backwards and forwards to have the resultant moment first clockwise and then counter clockwise. In other words, the pole tries to fall first one way and then tries to fall back the other way. So on average it seems to stay balanced. I'm still thinking about the rest of the physics of the plate which must have something to do with angular momentum. Why does it stay horizontal when it is moving fast enough but fall off as it slows?

Brick arch at Staveley Station

I was fascinated by the arch on the railway bridge at Staveley. The railway is not perpendicular to the road. If it were, the bricks would run parallel to the stones at the bottom. But the bricks must run perpendicular to the curvature of the arch. Arches transmit compression along the curvature. Bricks are excellent in compression but if they were not perpendicular to the curvature, there would be a sideways component of force on the mortar - a shear force. Mortar would not be strong enough to resist such a tearing force and the bridge would collapse.