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.