Dry ground makes it hotter

 

This was the ground in the Cotswolds last week: nothing like green Cumbria. I read an article that suggested that dry ground is making the heat wave worse. It goes like this: water has a higher specific heat capacity so any moisture uses up more energy per unit mass to reach the same temperature as earth. Then the water uses up even more energy turning into water vapour. This means that less energy is available to increase the kinetic energy of air molecules so the temperature can't get as high.

Oulton Tractor Run: what's that got to do with Physics?

 It was the wonderful Oulton Tractor Run today for charity so I looked up Physics and Tractors. It turns out that someone in Minnesota has realised that teaching Physics in terms of tractors might get more interest. The derivation in the slides models the Physics of a tractor pull and shows that the force needs to increase linearly with distance.

Emptying the pool

 It took 3 adults to tip the pool to empty the dirty water.

I'm estimating that the pool is 2 metres long by 1 metre wide. When we started, there was about 30cm of water in the bottom. A volume of 0.6 cubic metres of water of density 1000 kg/m^3 means 600kg of water. That's 10 times me!

We tried tipping it along the log edge and couldn't get the water over the lip. Mrs B suggested tipping it along the short edge and we managed it. Why did it work? One idea is moments. We had a bigger distance from the load so less force was needed. I'm not convinced this is the whole answer because of how the weight of the water distorts the plastic. We had to push close to the load which negates the idea of bigger distance. It might also be to do with being able to bunch up more on the short edge so that the water couldn't flow into pits between us.

Will I be able to react in time?

 

The drought down south means that the trees are shedding leaves sooner than expected. I was lying in the shade under this conker tree and hoping that the conker directly above my head wasn't about to drop. Would I be able to react in time? It was 3 metres above me. Using s=ut+1/2at^2 means that it would take 0.8 seconds to fall on me. If my reaction time is 0.2 seconds I might just be able to take evasive action.

Is this an electric motor at Saddlestone Quarry?

 

Bramley Engineering still seem to make lifting gear. This shed is above a big cable that goes down the hillside on Coniston Old Man. Looking at the hollowed out shell below, I think that the two angled metal bars with cupped tops might be stator cores for an electric motor. It is rusty so they are definitely ferrous. The idea of an electric motor is that electric current flows in a rotor and basically acts as an electromagnet that repels from a permanent magnetic field. In many motors, the "permanent" field is actually provided by proper electromagnets. These are coils wrapped around iron cores and are called stators because they don't move. These certainly look like stator coils.

This is the shed at Saddlestone Quarry in which the engine is housed.

The Winchester measure and enforcement of common weights and measures

 

I've been reading EP Thompson's book "Customs in Common". He spends a lot of time describing the way ordinary people tried to avoid being ripped off when buying grain and the way that there were sometimes price spikes that precipitated riots. I have posted before about the difference between the American gallon and the British gallon. The former was based on a volume of grain called the Winchester. EP Thompson describes how an Act of Charles 11 tried to set this as a standard across England for corn purchase but that there was resistance. He says that traders wanted to keep things uncertain and not standardised but that ordinary people also thought the Winchester was ripping them off because it was smaller. 

Back in the Keswick tunnel

 We were back in the tunnel on the Keswick to Threlkeld track. I was able to notice that there are echoes this close to the end. I wondered whether it was the cladding but it did seem to be the same even into the brick section.

However, as reported previously, the mid-section was acoustically dead. So is it an end effect? Is it an echo more from the change in acoustic impedance rather than from the walls?