Ca' the yowes to the knowes

 

There was a shepherd calling a sheepdog in Langdale which reminded me of Robert Burns' song. More to the point, there was a clearly discernible echo from Pike Howe crags. Map measurements suggest that direct sound came from 100m away (red arrow) and that the reflection travelled 150m there and 250m back. The difference is 300m of sound travel. That gives about a second which would be noticeable as an echo. I think it might have been less but it is hard to tell which part of the crag is reflecting the sound. The yowes ended up on the Howe in this case.

Phase difference in the shadows

 

The shadow pattern for the beads on this blind attracted my attention. The beads almost hang in a sine curve. With the shadow, you can detect phase difference. A shows a phase difference of pi radians (180 degrees) because when the shadow peaks, the beads are in a trough. At B the phase difference is pi/2 radians (90 degrees) - when one peaks the other is at equilibrium. C is an entirely positive curve and not unreminiscent of the kinetic energy graph for the motion.

Why sunlight is less intense if it hits at an angle

 

Look at the image of the Ukraine flag on the floor. It is much bigger than the size of the original on the window and yet the same light that passed through the original is present in the image on the floor. No extra light has appeared to make it bigger. So the same energy is spread over a bigger area - the intensity is reduced. This has happened because the light hits the floor at a more acute angle.

More thoughts on radiation dose and non-stochastic

 

The sun's been out and I've been trying to get a tan. I spent hours in the hills yesterday but you can't tell. This got me thinking about what radiation dose means, based on what I read on the website I linked in 2 days ago. I was wondering whether low intensity but for hours equals a high dose like high intensity for a few minutes. Maybe the sum of the energy will be the same but not the effect. That's probably at the root of the stochastic/non-stochastic distinction. Low intensity may not burn but there is a very low chance of genetic damage. The longer I go on, that is the only effect. But in mid-summer at higher intensity, I can burn in 10 minutes. That's a non-stochastic effect.

Thinking about absorbed dose

 

I found a great website explaining radiation dose here. It explains radiation dose in terms of sunburn. So the longer the time, the bigger the dose and the more intense the sunlight, the bigger the dose. I think exposure time is stochastic, certainly for low doses and that in medical terms, you can say that limiting exposure time limits stochastic effects. In the picture above, I am investigating aluminium shielding with a beta source and a Geiger counter. In medical terms, barriers or distance in air reduce the intensity and thus reduce non-stochastic damage.

Another way of thinking about stochastic processes

 

Imagine a dice game where you win a chocolate if you throw a double six. There is a fixed chance of throwing the double six but the more times you throw the dice, the more likely you are to win. However, the prize is the same no matter how many times you have to throw the dice. So the longer the time, the more likely the effect, but the effect is the same regardless of how long it takes.

Thinking about stochastic and non-stochastic

I've been thinking about stochastic and non-stochastic processes in radiation health issues. Stochastic basically means down to chance. In stochastic processes, the effect is independent of the dose received but the bigger the dose, the higher the probability of receiving that effect. I started thinking about driving. Careful drivers are unlikely to have an accident - there is a low probability. But obviously, the more hours you drive, the more likely to have an accident. The insurance companies know this - that's why the higher the mileage, the higher the premium. But driving a higher mileage doesn't make the damage worse in any given crash. That's why I think it is a stochastic process. Now think about reckless driving. If you deliberately drive at higher and higher speeds, then there will be a direct link between the speed and the severity of the accident. This is a non-stochastic effect.
 

Cod liver oil tablet is like the lens in your eye

 I noticed that a cod liver oil tablet was magnifying the weave in the tablecloth. Also notice how it focuses the light behind it.

Mrs B pointed out that you can change the focusing properties by squeezing the tablet so that it acts like the lens in an eye being stretched and squashed by the ciliary muscles.

Pitch drop experiment

 

This tanker reminded me to look up what is said to be the world's longest running continuous experiment. And I was pleased to find that I could watch live! I did think that the liquid diffusion experiment that Lord Kelvin set up Glasgow had been going for longer. I'm sure I saw it on Adam Hart-Davies' Local Heroes.

How far is infinity?

 

The size of infinity is a vexed topic. "An infinite distance" is an important concept in gravitational fields because it is the point of zero gravitational potential. This is because Newton's Law of Gravitation, which is an inverse square law, shows that the force of gravitational attraction is zero at an infinite distance from the Earth. It is then impossible to store gravitational potential energy by doing work against gravitational attraction. So to find the distance to infinity, one way is to hang a mass on a spring balance and travel outwards until the reading says zero. The distance will be finite and will actually be based on the resolution of the spring balance. Hence different spring balances would give different infinities!

Refracting not reflecting on the war in Ukraine

 

We bought The Guardian on Saturday and it came with a poem by Simon Armitage about the war in Ukraine. You can read the article on this link. He talks about a "refracted version of the obscene images". That interested me because people usefully talk about reflecting on events. Both are good physics words. Simon Armitage is one of the best users of the English language. So what could he mean by "refracted"? I guess in the sense that refraction bends light, sometimes leaving images distorted - but then twisted mirrors produce strange reflections. Refraction makes things appear at the wrong depth. Also it helps to focus. The news images have been horrifying and disturbing. It was good to note that so many Physics Nobel Laureates had signed a protest letter in the same newspaper. Read the poem here.

Stationary wave in a closed-end pipe

 

In this experiment, I put a piece of waste water pipe into a sawn-off lemonade bottle of water. I hit a tuning fork and held it over the end. I moved the pipe up and down to find the loudest response from the pipe and measured the height from the water surface to the top of the pipe. I tried it with 8 different notes.

There is a node at the water surface and an antinode at the top. Actually the node is a small unknown distance above the top of the pipe, called the end correction e. h+e is a quarter of a wavelength. Here's a bit from my worksheet showing how the equation is manipulated:

So I plotted 1/f on the y-axis against h on the x-axis. The gradient is 4/c so it can be used to calculate the speed of sound. The y-intercept is 4e/c so the end correction can be calculated from that.

How fast should I burn my gas?

 

The gas canister is almost empty and the pressure is low. Does it make any difference whether I let the gas burn full or go for a more restricted flow? This must alter the power because if less gas comes out every second fewer joules will be released. The stove heats the kettle and the water. The the hot metal also heats the air around it. If the energy flow into the water matches the flow from the system out into the air, I think we would reach thermal equilibrium. So I'm wondering if I run the gas lower whether it would be more likely to reach some kind of thermal equilibrium and stall in terms of temperature rise. I need to think about the equations for heat output from the kettle into the air.

More thoughts about the windscreen

 

The way the sunlight was reflecting from the ice goes some way to explaining why the ice doesn't melt in 2 seconds when the sun hits it. Perhaps the ice can be said to have a high albedo. Most of the energy is reflected straight back, Also, the darker parts of the windscreen are absorbing well and it melts there first (see below). This must be like the idea that a polar bear has black skin under the white fur. My calculation also neglected the fact that the glass will absorb as well and warm up. Can the ice melt if the glass is still 0 degrees Celsius?

melting the ice on the windscreen

 

We have had some sharp frosts again. At least the sun is helping at the moment but how long does it take the sunlight to melt the ice. Windscreen is 0.7m x 1.1m so about 0.8 square metres. Estimate a 2mm thick ice sheet. Density of ice = 0.9 kg per cubic metre approx so mass of ice = 0.8 x 2x10^-3 x 0.9 = 1.5 x 10^-3 kg approx. Say that the ice starts at -2 degrees C. To heat it up to zero needs mc.delta(theta) = 0.0015x2100x2=6.3 Joules. To melt it needs E=-mL = 0.002 x 340000 = 680 Joules. Max solar power = 1400 Watts per square metre. Let's halve that for low sun in spring. So from the sun we get 700 x 0.8 square metres = 560W. If it only needs 686 Joules to melt it, that would take less than 2 seconds full on. It takes longer because the glass is also being heated and the windscreen is heated only a bit at a time.

Trying to understand how potentiometric titration works

 

I made a cell by placing magnesium and copper electrodes in sodium chloride solution (salt water or brine). The potential difference due to the reactivity difference is in milliVolts. I am thinking that in potentiometric titration, there is a similar set up with two electrodes in a solution. Another solution is run in from a burette and this affects the potential recorded. The stuff I've read about potentiometric titration is complicated. There is a lot of talk about Gibbs' Free Energy - I can't do that yet. So this is my opening thinking on the subject.

Diffraction pattern on the water

 I have blogged about these striped patterns on the water before. They look like the diffraction pattern from a single slit.

Today I got to see how they are formed. This stream near Great Orton goes over a very small bump at A. That's enough to create bubbles. The bubbles drift downstream and deflate. I wonder if it is a surface tension effect, perhaps hydrophobic or some such, that pulls them apart into rows. The spreading of the rows sideways will just be the fast flow slowing and broadening.

Laminar and Turbulent Flow on the way to the head of Hope Gill

 

Near the head of Hope Gill (Clue: think Hopegill Head!) we foud this rock. The flow across it is mostly laminar. You can tell because the water is transparent. But there was a tiny section circled where the flow went turbulent on that top surface. It then goes turbulent off the edge as it speeds up and will increase the Reynold's number. A slight variation on the surface of the stone must be causing that to happen.