Brownian Motion and the Whitley Bay smoke cell

 Robert Brown first noticed the weird random agitation of particles by looking at pollen in a microscope. These days we look at smoke particles injected into a pot that can be illuminated from the side. This is called a Whitley Bay smoke cell.

 Einstein explained what was going on in 1905 by saying that the big visible smoke particles were being hit by tiny invisible air atoms. I modeled this by putting a table tennis ball into my kinetic model that creates a random motion of ball bearings. The ball bearings move randomly and that makes the table tennis ball move randomly as well. Einstein's analysis finally proved the long-postulated and assumed existence of atoms.

And special thanks to Di for her perseverance in getting the cell to work for us :)

Fractional distillation

I teach about the fractional distillation of crude oil. Crude oil is a mixture of liquids with different boiling points. The bigger the hydrocarbon chain the more energy that has to be supplied to overcome the forces holding the particles in the liquid. You heat them to vapourise all fractions except one and then send them up a column away from the heat source so that the temperature drops. One by one, each fraction falls below its boiling point and condenses back to a liquid. I demonstrate with a water and ethanol mixture. Both are boiled at the bottom and both vapours head up the column. It is fixed so that the temperature at the top is 78 degrees Celsius so that the ethanol condenses there and liquefies. The ethanol flows out down the side pipe. Much of the water vapour has already condensed as it fell below 100 degrees Celsius. It dribbles back down the inside of the fractionating column. There will still be some water vapour left at 78 degrees C but the ethanol solution is now strong enough to catch fire.

Spring constant in Dale Bottom

The gate across the footbridge below Low Nest Farm was very stiff. I can lift my whole body weight with one leg but an arm is weaker. Say I can push with a force of 200N. We can work out the force on the spring by equating moments measuring the distance from the hinge. Spring to hinge is about 3cm and hand to hinge is 30cm. This gives a force on the spring of 2000N. If the spring obeys Hooke's Law then force = spring constant x extension. Spring constant is how many Newtons of force  the spring needs per unit extension. It used to be called the stiffness of the spring and sometimes gets called the stiffness constant on exams. F=ke. So k=F/e. If the extension of the spring is 10cm or 0.1m so k=2000/0.1 = 20000 N/m.

Bunsen Burner and Bernoulli

It occurred to me yesterday that the Bunsen Burner works by way of the Bernoulli effect. That says that when a gas flows, it has lower pressure. Thus when the hole at the bottom is opened, the air outside will have higher pressure than the flowing gas inside. The pressure difference pushes the air into the flowing gas so you get a mixture of air and gas at flowing up the middle of the Bunsen Burner. A proper gas/air mixture burns at a higher temperature hence the blue flame. I suspect that with the air hole closed the gas reacts with the oxygen around the outside so combustion is not as complete.

Mistletoe in the Cotswolds: photosynthesis

We found amazing amounts of mistletoe in the Cotswolds. I've just been teaching the more detailed version of the photosynthesis reaction for the first time. The mistletoe must be using the light at this time of year when the leaves are off the host tree. The light dependent reaction uses the photon energy to split water. The hydrogen is taken to reduce NADP. The energy is also used to add a phosphate group to ADP to make ATP. NADPH and ATP are then the energy providers for the Calvin Cycle which turns carbon dioxide into sugar.

Cloud inversion at Stow-on-the-Wold

Having experienced the air getting colder as we reached the valley floor at Buttermere before Christmas and seen evidence of the denser cold air layer of a cloud inversion, we found this lovely example in the Cotswolds after Christmas. The clear skies meant that the Earth's surface was able to radiate a lot of thermal energy into space during the night; the humidity was right for fog to form; the Sun's energy heated the upper layers of the atmosphere first and the cloud vanished but the lack of sunlight reaching the surface delayed the warming of the surface of the Earth resulting in a cloud inversion. But because Stow is on a hill we were in the sunshine and were able to see the very rare Blue Rock Thrush, which is on the chimney in the picture below!

Wrap yourself in foil to keep warm

It has always seemed strange to me that you can keep yourself warm with just a thin piece of foil but that's exactly what a lot of runners do. It shows that we must lose a ot of our heat as infra-red. Suppose that I am 2 metres high by 0.5 metres wide. That might give a total area of 2 square metres front and back. By Stefan's Law where P = sigma x surface area x absolute temperature^4, and with 37 Celsius being 310K I get an output power of 1.1 kW. Googling suggests other people are getting 100W.