The Moon and albedo

I learnt a new word recently: albedo. It means the fraction of incident light that is reflected from a surface. The Moon is a pale colour and quite bright so I expected that it would reflect a lot of light. It turns out that the albedo is 0.12 which means that it reflects back 12% of the light from the Sun that hits it. The suggestion is that the rest of the energy goes to heat the Moon. http://www.asterism.org/tutorials/tut26-1.htm

Going round in circles: shrimp boat at Silloth

The Jaana B was off the promenade at Silloth. The water being pumped out of the side was pushing the boat round in circles. This is due to two of Newton's Laws of Motion. The second law says that the resultant force is equal to the rate of change of momentum. Now the water is changing momentum when pumped, going from no speed to speed v. If the rate of mass flow is dm/dt (ie m kg per second), then the rate of change of momentum is v.dm/dt. By Newton's Third Law, if the boat pushes on the water, then the water pushes back on the boat with the same size of force but in the opposite direction. Since the pump outlet is off centre, a resultant torque is created which drives the boat round in a circle.

Stationary waves and particle flow

We found some amazing stationary waves on the beach at St Bees where the stream flows out into the sea. The point in a stationary wave is that there is no energy transfer. But it has been bugging me for a while that particles flow through the system. It is a bit different to a guitar string where the same bit of wire vibrates up and down to form the wave. Here the peak stays fixed, not wobbling up and down. Particles of water flow through it all the time. You can say that if the peak is fixed in place, it doesn't ever break and transfer energy like the progressive waves on the sea. However, surely the particles carry kinetic energy. Maybe it is because the system is a steady state: same mass flow in and out. Still thinking about it...

Colour temperature and the Moon

Earlier in the year Simon Ingram wrote a piece in Trail magazine in which he mentioned that the colour temperature of the Moon is about 4000 Kelvins. I know that the Moon is nowhere near that hot so it led to some frantic research. It is linked to the idea of blackbody radiation and is likely to have a link to Wien's Law which links the wavelength in metres of the maximum intensity to the temperature in Kelvins: lambda max x temperature = 0.0029. The background is here https://en.wikipedia.org/wiki/Color_temperature The Moon is reflecting light from the Sun but has a lower colour temperature so the reflection must be affecting the light. This is not true blackbody radiation because it is not radiation given out due to the temperature of the Moon. A lower temperature means a peak in the redder end of the spectrum which is apparently experienced as yellower light. See https://physics.stackexchange.com/questions/244922/why-does-moonlight-have-a-lower-color-temperature Simon Ingram also wrote about the Purkinje Effect so I need to follow that up next.

Puffer on the canal at Crinan: coal for Vic 32

 We found this pile of coal by the canal at Crinan. I've used the formula for the volume of a cone: height 1.5m, radius 1m gives a volume of 1.57 cubic metres. Coal varies in density but an average value might be 800 kg per cubic metre from a little searching. That gives about 1250 kg of coal. I found the energy density quoted as 24 million joules per kg so the pile might be worth 30 billion joules.

 I looked up Vic 32. http://savethepuffer.co.uk/puffer-specifications/ Data says 120 horse power. That's 88260 Watts. Power = energy/time so time = energy/power = 30 billion / 88260 = 342000 seconds. That's nearly 100 hours or 4 days coal.

Not the king of Scotland: shoe size on Dunadd

We visited the hill fort at Dunadd where they made the kings of Scotland when the first settlers from Ireland arrived 1500 years ago. The idea was that the would-be king put a foot in the imprint in the rock. The notice said it is size 6. They must have been smaller back then. I use show size as an example of discrete variation. If we measured people's feet and found foot lengths of 13cm and 14cm, we could easily find people of 13.1cm, 13.2cm etc. This is continuous variation. But between size 5 and size 6 there is only size 5.5. They don't make size 5.28. That's what makes it discrete.

Solar powered markers on the Falkirk canal path

It took us a while to work out what these were. They were set into the canal path every couple of meters. It was obviously a solar voltaic on top but I had to get down to see that there were LEDs set into the sides. We found two on in broad daylight. LEDs draw such a low current that they are ideal for working on solar power in the north.

Water pressure pushes equally in all directions

Someone has made this piece of apparatus to show that at any given height, the water pressure pushes equally in all directions. A previous idea had been to put pin holes in a balloon and put it over the tap. Filled with water, the little jets should be the same whether they go up, down or sideways. It did cause a mess though!

Swing bridge at Falkirk Wheel: rotational dynamics

I have been wondering about how much force a human can muster in a push. Mrs B reminded me that it could be done from the weight machines at the gym. I think a mere mortal might push-list 30kg. The weight lifter winner at the Commonwealth Games was nearly ten times that! Say the bridge is 4m from the pivot to the end. For a 30kg push, the torque is 300N x 4m = 1200Nm. Moment of inertia = 1/12 ML^2 for a central axis. Here L=8m. How big is M? Suppose all the wood fitted down into 8m x 0.5m x 0.5m = 2 cubic metres. Suppose the wood floats so say 900 kg per cubic metre. Mass = 1800kg. Torque = moment of inertia x angular acceleration. So angular acceleration = 0.67 rad per second per second. Suppose it reached 0.67 rad per second after 1 second and stayed at that. To do a quarter of a turn = pi/2 divided by 0.67 = 2.3 seconds. A bit low but not ridiculous. I wish I'd timed the motion but it can't have been that small. Mass must have been bigger.

Beware golf balls

This is on the coast path from Allonby to Maryport. Golf balls have dimples to make them go further. A smooth ball does not disturb the flow of air over its surface. The air stays in fixed layers - called laminar flow. These are like onion skins of air and give the ball a larger surface area. The dimples mess up the flow of air making it turbulent. The turbulent air sticks closer to the ball reducing the surface area it presents and thus reducing drag. Some years ago I revised Reynold's Number for the laminar/turbulent transition. I need to look up how this relates to golf balls.

Greendykes Bing: was the shale industry energy efficient?

The landscape of West Lothian is littered with these enormous spoil heaps. The y are a relic of the Victorian shale oil industry that meant that Scotland was exporting more oil than any other nation at the time. The spoil heaps are called bings. This one is estimated to contain 15 million tonnes of waste. Another statistic is that 7 tonnes of waste rock were produced for every 10 barrels of oil. I looked up the energy in a barrel of oil https://en.wikipedia.org/wiki/Barrel_of_oil_equivalent I'm using 6 x 10^9 Joules. So 10 barrels would produce 6 x 10^10 Joules. Energy would be needed to bring the 7 tonnes of rock to the surface. If mgh = 6 x 10^10, using mass = 7000kg you get a mine depth of nearly 1000 km. Even allowing for heat energy used in the extraction process, it seems as though the oil would be worth the energy expended collecting it. Here's a lovely film showing the bing in all its glory https://www.youtube.com/watch?v=v5wiv5zobAQ

Thinking of overtones on the canal in Falkirk

I was amazed to find "The Undertones" still painted on a wall by the canal in Falkirk. It must have been there nearly 40 years. In Physics, we have overtones. This applies to the stationary waves produced by instruments. The longest stationary wave to fit into an instrument is called the FUNDAMENTAL MODE. It is fixed by the boundary conditions: for a guitar string that means a fixed point or node at each end. The higher frequencies that also fit in are called OVERTONES.

My pan is a closed system

Back to the new way of teaching energy, based on the First Law of Thermodynamics. My pan is a closed system because with the lid firmly on, matter cannot get in or out. By that I mean stuff made of atoms like water or steam. But the water inside gets hotter so something must be getting in. And that is how we get to the idea of heat and work crossing the system boundary. Since the pan is rigid, no work is done here. The new guidelines suggest breaking up "heat" into two pathways: heating by radiation and heating by particles. The shiny tin is opaque - basically imprenetrable to infra-red. So it must be "heating by particles" ie conduction.

How far away is that bird? White-winged Scoter at Musselburgh

 There's an American White-winged Scoter out there somewhere amongst the Velvet Scoter but just bobbing up above the waves for a split second at a time. Reports said 300m off shore but it looked a lot more to me. So I decided to work out how to apply the little finger trick to my telescope. The island of Inchkeith subtended half a little finger to my eye, which is about half a degree but through the telescope it took up about half the field of field.

 Conclusion is that the field of view at 40x is one degree or 0.0175 radians. Well, let's say 0.02 radians as this is all very guesstimated. I tried to photograph a duck in the distance but all I managed was a gull left of centre below. Measurements suggest it subtends about 0.0004 radians. Wingspan is about 1.20m. By the arc length rule, distance is therefore 1.20/0.0004 = 3000m. This might be inaccurate but it is clearly more than the 300m quoted. Inchkeith was 10km away as measured on a map. I can only dream of seeing the ducks that close!

CTR Wilson in the Pentland Hills

I was very pleased to come across this memorial to CTR Wilson at the foot of the Pentland Hills near Edinburgh. He won the Nobel Prize for Physics for his invention of the cloud chamber. This blog started after a trip to Ben Nevis and it was his time as an assistant at the observatory on the top of Ben Nevis that inspired him to invent the cloud chamber. This invention was one of the earliest particle detectors and thus on the direct line of development that led to CERN. I've posted about cloud chambers before when we have had dry ice in. I found this wonderful set of anecdotes about his life https://www.rse.org.uk/cms/files/events/reports/2012-2013/CTRWilson_Conference.pdf which has a piece from someone I assume to be THE Tam Dalyell, the famous Labour MP, whose interest in science seems to have stemmed from a chance meeting with CTR Wilson.