Will Mardale appear from Haweswater this year?

This is Haweswater, a reservoir near Shap south of Penrith that feeds water down to Manchester. The reservoir was made in the 1930s by building a dam and flooding the valley. There used to be a village with a church and a hotel which was demolished and flooded. The village was called Mardale and sometimes reappears when the water level falls a long way. Check out the wonderful Striding Edge website to see what the lake level was like 3 months ago http://www.stridingedge.net/Walks/2014/04.%20Apr/29.04.14.htm I am estimating that the level has fallen by 5 metres. They say it had fallen 23 metres to give the view shown in the bottom picture. The lake is roughly 6km long and 1km wide. That would give a volume of 6 million cubic metres lost in  3 months. It has hardly rained so that suggests Manchester uses about 500 000 cubic metres a week from the reservoir. The catchment area of the streams that feed into the reservoir is roughly a circle of radius 4 km if you measure a map. That gives an area of 48 million square metres. It would need to be filled to 1.5 metres to replace all of that water. Seathwaite in the western Lake District is famously the wettest place in England with about 3.5 metres per year, so that amount of rainfall is not a bad estimate. For photographs and maps of the old Mardale, try http://www.mardale.green.talktalk.net/map%20index.htm The square object in the third photograph is likely to be part of Grove Brae Farm. If it doesn't rain a lot, I suspect it will be worth another visit in September to see if the village has appeared.

Preparing for Lower Sixth Physics #12: Newton's Second Law and Spaghetti Junction

We have said before that you carry on in a straight line at constant speed if there is no resultant force on you. Newton's Second Law deals with the case when there is a resultant force. If you carry on in a straight line in those circumstances, you either accelerate or decelerate. The size of the acceleration or deceleration is inversely proportional to mass. In other words, if your car is twice as heavy the acceleration will be half as big. Now consider what happens if there is a resultant force but the speed remains the same. The photographs show the top of the wonderfully named Spaghetti Junction on the M6 in Birmingham. You can see a road over the top in the first photograph. In the second photograph it loops round and down, going underneath - hence the name because other roads twist round these two. If you go round the flyover at constant speed, you are changing DIRECTION so your velocity changes. So you are still accelerating. This time the resultant force is directed towards the centre of the loop and is called CENTRIPETAL force.

Sheep tracks and equipotentials on Knott Rigg

Here's a view out over Knott Rigg and Newlands Hause. Look at the sheep tracks on the side of the mountain. Sheep go sideways around the mountain mostly. They are not stupid in this regard and try to expend as little energy as possible. If they don't go up or down, they keep the same gravitational potential energy. Thus the sheep tracks could be called EQUIPOTENTIALS. I spend a lot of time drawing these for various types of force field. Incidentally, the force field lines are always at 90 degrees to the equipotentials. And since gravity points downwards, that is the case here. Sheep tracks look like well made paths and are a common reason for getting lost. Most horizontal paths in the Lake District mountains are not human made.

A picture of physics: Crummock Water and the Solway

You might not think that this picture has a lot of physics in it but think about this. First there are the cumulus clouds formed by evaporation and convective rise. Then condensation when the temperature drops below the dew point. But condensation releases heat energy by latent heat which causes expansive rise upwards and hence the fluffy tops. Then there is the perfect reflection in Crummock Water. And if you enlarge the photograph you can see the massive wind farm at Robin Rigg in the Solway beyond. So there is a lot of physics in the picture.

A weather front on the way

I have always known that high wispy cirrus cloud means that a front is coming and rain will be coming soon but yesterday I was able to watch it happening with reference to a diagram in a book. This is what I saw. First came the cirrostratus.

 

 Behind was some altocumulus on the right, followed by altostratus which was a solid layer covering the whole sky.

The photographs were taken at 4 o'clock and it rained heavily at 9 o'clock. These clouds are typical of a warm front coming in off the Atlantic. I wonder if similar systems occur in other parts of the world like Australia?

Preparing for Lower Sixth Physics #11: Newton's First Law

Everybody knew that if no forces acted on an object that was stationary, it would remain stationary. It took Isaac Newton to extend that to moving objects. Take the car in the photograph, going at a steady 70 mph in a straight line. Newton pointed out that the forward force of the engine must be exactly equal to the frictional forces acting on it. So overall, taking into account that backwards forces are given a negative sign, the forces all add up to zero. We say that there is zero RESULTANT force. Newton said that if there was zero resultant force, an object that was stationary would remain stationary and one that was moving in a STRAIGHT LINE at constant speed would continue to do so. Being stationary and going in a straight line at constant speed are stable conditions.

On the meridian in East Yorkshire

We went to Spurn Point in East Yorkshire: go to Hull an keep driving for 45 minutes. On the way we found the monument in the pictures above. We had crossed the Greenwich Meridian. The north/south line on the Earth is obvious: it's the Equator. The east/west line isn't obvious and was set up by human choice. It runs through Greenwich in London because that's where the astronomers who did the work on it were based. Your distance east or west affects the time for things like sunrise and sunset. We would say that it was midday when the Sun was highest in the sky. If you fix your watch so that it says 12 noon when you are stood on the Greenwich Meridian, your watch will be showing Greenwich Mean Time or GMT. In Wigton, we are 3 degrees west of the line. 3 out of 360 degrees over 24 hours adds up to 12 minutes. 12 noon arrives here 12 minutes after London.