Joules and Keswick

James Joule did his research on energy nearly 200 years ago. I was reading about his experiment where he allowed a falling weight to turn a paddle wheel in a barrel of water. He measured the temperature of the water. It went up because the mechanical work gave extra kinetic energy to the molecules in the water. I was thinking about trying to recreate it in my lab. Suppose I allowed a 1kg mass to fall 1m. It would lose mgh = 1 x 10 x 1 = 10 Joules of gravitational potential energy. If all of this went to raise the temperature of the water I'd be using dQ = mcdT. Say I used a 1 litre tub of water. The mass of water would be 1kg. Specific heat capacity of water = 4200 J/kg/degree C. So change in temperature dT would be 10/4200. To get a convincingly large temperature rise I'd need a much, much larger mass to fall through a much bigger distance. I wonder what he used...

Kettle handle at Haughtongreen bothy

This bothy is just off the Pennine Way north of Hadrian's Wall. Whilst we were there, I noticed that the kettle handle is black. Closer inspection reveals that the kettle itself is aluminium so that it won't rust. It is silver because that colour emits infra-red heat radiation badly. You don't want the main kettle to be emitting too much heat radiation because that would be inefficient. But the handle needs to stay cool. The handle is made of steel - you can tell from the rust. The black is enamel paint. It could be that black emits heat radiation better making for a cooler handle. But the handle is shiny enamel which isn't good. It's probably just that someone randomly thought that black would look better.

Thermal decomposition on Hadrian's Wall

We came across these limekilns on the north side of Hadrian's Wall near Housesteads. There was clearly a low ridge of limestone amongst the igneous intrusions. The used to dig out lumps of limestone and drop it into the kiln, having got a raging fire going at a temperature of over 1000 degrees Celsius. This is the reaction that took place.

The heat energy makes the calcium carbonate molecule fall apart to produce calcium oxide and carbon dioxide. It must be an endothermic reaction because we had to heat it up to get it to work.

Calcium oxide is a white powder that is often called quick lime. If added to water, it makes calcium hydroxide, which is often called slaked lime. Here's the reaction:

This is a very exothermic - it can give out a dangerous amount of heat energy. The calcium hydroxide is an alkali because of the OH- ions in it. OH- is called a HYDROXIDE ion.

The reason for doing all of this is that farmers can put the slaked lime alkali on their fields if the soil there is too acidic for growing crops. The calcium hydroxide can neutralise the acidic soils. The moorland soils in this part of the world are naturally acidic.

Flat topped clouds over the Tyne Valley

This was taken from Housesteads, looking towards Newcastle. The cloud in the middle spreads flat across to the left. Not quite the typical incus cumulonimbus anvil shape but not bad. I had an idea that it was caused by convection hitting a temperature barrier and being forced sideways. A bit of research has revealed that in the layer of air closest to the Earth which is called the troposphere, the temperature of the air does fall with height. The measure of this is called the lapse rate, in degrees Celsius per km. Hence convection works because the sunlight warms the ground and the ground warms the surface layer of air. This expands, becomes less dense and floats upwards. I teach that it will then cool, shrink, become more dense and sink. But I'm thinking about how the bubble of warm air will lose the internal energy needed to lower its temperature. How efficient would conduction be? Is it through adiabatic expansion? But the next detail I learned is that temperature goes the other way in the stratosphere, the next layer up. It is coldest where it butts up against the troposphere and then warms up as you increase in altitude. This would put a stop to convection and is why clouds spread sideways. But is the cloud in the picture really tall enough to be at the top of the troposphere? That would be 10km up. Hard to judge. I should have measured the height of the aeroplanes with my little finger method.

Nuclear display boards

Mass spectrometer

I found this mass spectrometer in a museum in Manchester. It works by turning the atoms in a compound into ions and then bending them with a magnetic field. They all experience the same magnetic field but the heavier elements are not bent as much so they are detected further from the centre of the circle. One clever bit is the use of crossed electric and magnetic fields on the way in which only allow particles of a particular speed to go straight on through a slot. It means that the speed in the main detector is also a control variable. Unfortunately we can't assume that the ions of one element all have the same charge. Some will be +1, some +2 etc. But you can make allowances for that in the analysis. Read the notice in the photograph to see what they are used for.

After the eclipse

 I didn't get to use the eclipse glasses on Friday so we took them onto the fells above Grasmere today. It was still very bright even through the aluminised Mylar plastic film. It's not far off trying to see through kitchen foil! It's important that the filters don't let infra-red or ultra-violet through because these can also damage your eyes. I'm now thinking of ways to test my eclipse glasses at these wavelengths. My eyes seemed all right through my polarising sunglasses AND the eclipse glasses. I aimed to be as protected as possible...

A solar eclipse comes with a very high tide because the Sun and the Moon line up their gravitational pulls on the seas. There was a very low tide at Silloth on Friday night. And an eclipse comes just before the New Moon. So tonight there was a lovely crescent Moon with the planet Venus as a bright "star" just above it.