Colour theory with Mouses at Greenbelt

 Mouses were fantastic on the Rebel Rouser stage at Greenbelt. Here they are in white light. The drummer has a red shirt on. Colour theory says that white is made of red, green and blue mixed. The red reflects from the shirt into our eyes but the green and blue are absorbed.

Here they are in blue light. This time there is no red to reflect. The blue is absorbed so the shirt looks black.

In red light, the red reflects so the shirt looks red again. Nothing is absorbed by the shirt but we can't tell. Any white surface would normally reflect all of red, green and blue to appear white. However, here only red reflects and so any white surface also appears red.

Levelling the land: cut mark at Burford Church

 I've posted before about the way that they worked out the heights of places for Ordnance Survey maps by measuring angles up and down from one place to another across long cross-country journeys. This type from the end of Burford Church is called a "cut mark" for obvious reasons. I'd expected it to be from the First Primary Leveling from 1840 to 1860 but the journeys from Oxford to Bath and from Gloucester to London both go well south of Burford.

Ironically, the reason we'd gone to Burford Church was in homage to the Levellers.

Tractor Beam at Clarkson's Farm?

 

Does this count as a tractor on a beam? I was convinced that a tractor beam was the stuff of Science Fiction. This page claims not. I like the precise definition that the attractive field has to be collimated. Not sure that it doesn't sound like SF though. 

High pressure, higher temperature

 

The weather was very settled for the harvest on Clarkson's Farm this year. That's the famous Lamborghini tractor on the right. A high pressure system had resulted in very high temperatures. The Times newspaper on Saturday 6 August says that "temperatures will rise as the air is compressed in the high pressure like a bicycle pump heating up as the air is squeezed". I'd never thought of that. We're into the gas laws here. However, there are three variables to consider. Not just pressure and temperature but volume as well. So the assumption here is that the volume of the air doesn't change as the pressure increases, at least not much. I suppose that the volume of the atmosphere is constant but are we considering the whole atmosphere or just a sample of the air inside it? Need to think about that.

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.