If a tree falls in the forest...

We found this tree rocking backwards in the forest above Loch Rannoch. It reminded me of the old question: "If a tree falls in the forest and there is no one there, does it make a sound?" This gets to the heart of the definition of sound. Yes the falling tree will make the particles in the air vibrate, But by sound, we surely mean that those vibrations are detected and interpreted. That needs some higher life form. We were there and we observed. If it's fallen since our visit, then it didn't make a sound!

Basic principles of radar

I was teaching about ultrasound the other day. Radar works on a similar principle that a pulse is sent out and that some of it is reflected back. If you look at the trace in the picture, the amplitude of each reflected pulse is much smaller. In the same way as with an ultrasound scan, you use the oscilloscope trace to calculate the time it takes for the pulse to go out and to reflect back. Use distance = speed x time for your calculation. In this case it's an electromagnetic wave so it's the speed of light you need. The distance to the aeroplane is half your calculated distance because the pulse has gone out and back.

GCSE revision: why I think transformers are odd!

I remember once showing this to a class and they were underwhelmed. They said "we press switches every day and lights come on, sir". But what makes me think it is odd is that both coil A and coil B have insulated wires. Even though the core around which they are both wrapped is of iron, there is no way the current can get out of one wire and flow through to the other wire. Coil A is an electromagnet. The squiggly line is an a.c. power supply. That means that the poles of the electromagnet keep changing direction. This changing magnetic flux then waggles backwards and forwards in coil B because the flux can travel to coil B through the iron. As pointed out yesterday, waggling a magnet inside a coil produces induced electricity - that's what causes the bulb to light. We also showed that coils with fewer turns had a smaller induced voltage. That's how a step down transformer works.

GCSE Revision: Electromagnetic induction

We showed that if we moved the magnet up and down inside the coil, we got a reading on the voltmeter. In this case, south pole into the hole went positive and south pole out went negative. In other words, changing direction of movement makes the voltage flip from positive to negative so we have made AC electricity. It also works if you hold the magnet still but move the coil up and down.

You get the same thing if you move a copper wire up and down between the poles of a powerful horseshoe magnet. We say that there are invisible flux lines going from the north pole to the south pole which make up the magnetic field (it is possible to use iron filings to show them). The copper wire was chosen because it is not a magnetic metal. It cuts down through the flux lines like a cheese wire through cheese. As long as it is MOVING you get a voltage induced. Downwards made a negative voltage and upwards made a positive voltage.

Finally I waved the powerful magnet near the coil. It didn't even have to go into the coil to get an induced voltage. As it moved, the flux lines coming out from it cut through the coil. All of the methods shown are called ELECTROMAGNETIC INDUCTION. They are used in generators and make AC electricity.
The non-essential part is to say that they work by getting the magnetic field to drag electrons along inside the wire. Moving electrons = electric current.

A strange mapping

I have been experimenting with the panorama function on my camera. I have to spin gently holding the camera whilst it tales photograph after photograph and stitches them together in one big picture. So it is taking a curved 3D world and mapping it onto a straight 2D space. It must be related to those maps of the world where the globe has been cut like orange peel and squashed flat onto the page. Things get stretched and warped. Just so with this picture. Look at how the straight railway line in the bottom right of the picture has been pulled into a curve. This is similar to stuff I was reading in Roger Penrose's book The Road to Reality. He is dealing with how we cope with curved space-time in at least 4D.

Ground source heat pump at Croome

The idea is that they are going to bury a lot of pipes under the field in front of the house. In the winter it is warmer underground than above ground. There is a mixture of water and anti-freeze in the pipes. Thermal energy can get the from the ground into the liquid by travelling along the temperature gradient due to the temperature difference. The thermal energy is then taken up to the house. Sounds unbelievable but it works.

Pudding stone conglomerate on Conic Hill

An amazing feature on Conic Hill was the conglomerate rock. It had large rounded pebbles. It looked like concrete. They must have been transported a decent distance to have been rounded off like this. It was similar to the rock I found last summer on Rhossili Down. That was said to have come from a river delta millions of years ago. The visibility was so good when we visited that Arran is visible in the far distance in the top picture. Today I was at St Bees and saw pebbles on that beach.

Perhaps if I come back in millions of years time this will have become pudding stone. It puts the nature of time into some sort of perspective!

A transformer a little closer to home

This school laptop charger  has some data on the side. Suppose mains input voltage is 230V. It says input current is about 1.5A. That's a power of 345W. It says output voltage is 19.5V at 4.62A. That's a power of 90W. It would give the efficiency as 26%. Wow! There must be something wrong with yesterday's substation numbers because they would give an output current in the tens of thousands of Amps.

A transformer with radiators in Tewkesbury

This was a very open substation in Tewkesbury. They actually look like household radiators. They are not to keep the substation warm but are to radiate the wasted thermal energy into the air. I have just spent some time trying to find out the rating of this substation. It looks like it probably takes 11kV down to household voltage. I looked for a power rating. They are not quoted in Watts because they work on alternating current so there will be fluctuations. What goes for power seems to be measured in MegaVoltAmps MVA. I found a figure for one like this of 5MVA. So does that mean 5000000 Joules per second? If the transformer is 99% efficient that means 50000 Joules per second released. If that were true, suppose we tried water as a coolant. 50000 Joules would be enough to heat 150 grams of water from 10 to 90 degrees Celsius every second. This transformer will be oil cooled because oil can reach a higher temperature without boiling.

Not a cloud in the sky - why??

It's been a beautiful day in Wigton. Warm and with a clear blue sky all day. Just the sort of day in April you'd expect convection to get going and create cumulus clouds and cloud streets. But that didn't happen today. So what stops the clouds forming? Is it the wind direction? Or maybe the lack of wind today. Does it need to be coming in off the sea to bring the moisture with it? More observation required.

Highland Boundary Fault from Conic Hill

I had a very happy trip to Balmaha on Loch Lomond. Not only did I get asked my age when buying beer but I found the Highland Boundary Fault. I have posted before about living on the remains of the continental collision that brought Scotland and England together. What I didn't realise was that Scotland was formed from more than one island on the same continent that crashed into each other in the collision. The Highland Boundary Fault was the scene of one of these collisions. I like the idea that it can be traced across many countries and is part of the evidence that we were once joined to America. The movement of the tectonic plates is a lovely piece of Physics: convection of molten rock in the mantle drags them along.

They had this lovely model of what it looks like:

 We climbed up to look at the real view.

Centre of mass

I made this odd shape out of |Lego to test an idea about centre of mass. I have been teaching that the centre of mass is the point with zero resultant torque - ie the sum of the clockwise moments equals the sum of the anticlockwise moments. I balanced it on a knife edge to find this point.

 One problem that my class has had is that there are equal masses on either side of the balance point. This is not true. It is equal MOMENTS. So you can have less mass on one side provided it is further away so that it has a bigger moment. The results are shown below.

 They are clearly not equal parts!

In and Out on Ben Lomond

Here's the top of my flask and part of the view from the top of Ben Lomond. You can just make out the pipeline for the hydro above the flask. There are two arrows on the flask, indicating two openings. As you pour coffee out through one side, air is able to go in the other side to take its place. If the air isn't able to get in, the coffee won't come out. So in a sense it is air pressure pushing the coffee out of the flask.

Evaporative cooling of my coffee??

I made a cup of coffee and put it down to cool. Then I realised I'd put it down in front of the fan heater. Will it cool? The heater was increasing the air temperature around the cup. This would mean that there was a smaller temperature difference between inside and outside so the rate of flow of thermal energy through the walls of the cup by conduction would be reduced. But I noticed a lot of water vapour coming out of the top of the cup - more than usual. The fan makes air move. Water molecules with high high kinetic energy in the coffee can break through the surface tension and escape. This is evaporation. Only the molecules with the most kinetic energy can do this so as they escape the average kinetic energy of the rest of the water molecules is reduced. Thus the coffee cools due to the evaporation. But if the evaporated molecules hang around above the surface, they get in the way and stop further evaporation. The fan blew them out of the way, encouraging evaporation and thus cooling the coffee. An odd situation - a proper experiment with a thermometer would determine whether evaporation or conduction had more effect on the cooling.

Alternating Current on my oscilloscope

I connected a dynamo up to the oscilloscope. I used to have one on my bicycle when I was a kid. Turning the handle makes a magnet spin inside a coil of wire. The north pole drags the electrons one way and the south pole drags the electrons the other way. As a result, spinning the handle produces a positive and negative trace on the oscilloscope. This is alternating current (AC).

Direct Current on the oscilloscope

 I connected a battery pack up to the oscilloscope to show my class that the voltage doesn't change as time goes by with direct current. I then swapped the connections round to show that you then get a negative voltage.

 I did remember to pull the connections out completely to show that zero Volts is a line across the middle.

 But I did have to remember to flick the switch onto DC setting to get the oscilloscope to recognise what I wanted it to do.

White light and a diffraction grating

Today we looked at the white light from an overhead projector through a diffraction grating. The central spot will always be white because all wavelengths go together in the straight on direction. Since wavelength is colour, you get white because that's what all colours of light add up to give. However to the sides, you only get a colour where the angle means that the path difference is measured in whole wavelengths. That splits the colours up. Violet has a smaller wavelength so it doesn't have to bend as far to the side to have an integer path difference. Red with its longer wavelength bends out further before this happens. Hence the spectrum with violet closest to the centre and red furthest out. It is clearest under the two satellite white spots that are reminiscent of sun dogs. I'm not sure why they are there. Sun dogs are a refraction effect so the colours in a sun dog are the other way round. There were other interesting artifacts in the photographs caused by light leakage.

Trying to catch cloud streets forming

 It was a beautiful day in the hills today. There were amazing views back across the Solway plain. If you look at the photographs, you can see cumulus cloud beginning to form over Scotland. The land there will be hot enough to start convection. I posted about cloud streets last week, This time the cloud streets were beginning to take shape heading inland from there. So why no cumulus over Cumbria today? Further observations of conditions needed. If you look carefully at the second picture, you can see Wigton!

How long would Loch Rannoch last us?

Mrs B asked a wonderful question: for how many days would the water in Loch Rannoch could supply the UK? I had in mind to do a volume calculation as a triangular cross-section multiplied by the length of the lake. Google searches gave the depth as 134m and width as 1000m. Length is 15km. So volume = 0.5 x 0.134 x 1 x 15 = 1 cubic kilometre. I was pleased to see that was a volume someone else had come up with too. There are 10^12 litres in 1 cubic kilometre. The web reckons the average UK resident uses 150 litres per day. Wow! Population of the UK is about 65 million so we would use 9.75 billion litres a day. That means Loch Rannoch would last us about 100 days. It's a good job it rains a lot.

Parallel connection near Rumbling Bridge

Electricity supply has been an endless source of fascination when I've been out. I noticed this above The Hermitage at Dunkeld. The main line has 3 wires but the spur off up the hill has only two. They come from the middle and the furthest edge. So is the middle the common neutral of a.c. supply? If so, why are there two lives? It reminded me of a household ring main circuit where live and neutral spurs go to plug sockets from a central ring. They are wired in parallel to each other, as is this.More research to be done.

Measuring vertical on Schiehallion

I tend to refer to Schiehallion in Perthshire as the Holy Mountain of Physics because it was this mountain that the Astronomer Royal Neville Maskelyne used in the late 1700s to measure the mass of the Earth. My pilgrimage to the top in 2009 was one of the early topics on this blog. I have returned to the northern shores at Kinloch Rannoch. What Maskelyne did was hang a pendulum near the mountain. You'd expect it to be pulled vertically downwards towards the centre of the Earth but he had figured that the mass of the mountain would attract it horizontally and pull it away from the vertical. If he could deduce the mass of the mountain and measure the deviation from vertical, he could work out the mass of the Earth from Newton's Law of Gravitation. He considered using Skiddaw - you can see that from Wigton! Schiehallion has a similar shape, like a Toblerone bar, but is more remote from lother mountains that Skiddaw. They mapped it accurately by inventing contours right here to get the correct volume, They knew the rock density so they could get the mass. But how to measure deviation from vertical? This had always puzzled me and my classes. I know what is vertical by hanging a pendulum - but clearly not if the pendulum itself is out of line. I read recently that Maskelyne used the stars. He could calculate which would be vertical and then observed the position of a pendulum relative to these stars,

Dunkeld bridge: thinking about arches

Having written about the flying buttress at Tewkesbury I was sat looking at Thomas Telford's bridge across the River Tay in Perthshire wondering how I'd describe the forces acting on an arch. Start with the central stone. Gravitational attraction is pulling it downwards but it doesn't fall. There must be an equal and opposite push back upwards. This comes from the stones on either side. These are angled so that they have a vertical component pushing up on the block. But being angled, the block has a horizontal component pushing sideways on the blocks trying to push them out of the way. This is repeated on stone after stone until the little bit of extra angle each time has meant that what started out as a horizontal push by the middle block on the two either side has become a vertical force. The vertical load in the middle was transferred horizontally and became a vertical force at the sides. I was also thinking about the frictional forces between the stones and how much that acts to keep them in place. I had long wondered how you built an arch but discovered some years ago that they used wooden frameworks to hold the stones as they put them in.

Another ice house: Croome Court

This ice house turned out to be two thirds underground. It must have contained a huge mass of ice if filled. This would mean that even more energy would be needed to melt it making it last longer into the summer. I inspected the double wall construction. It wasn't clear what was in the gap - some sort of mortar. Maybe it is an air gap further round away from the door.

Flying buttress at Tewkesbury Abbey

With Medieval cathedrals, building high caused problems. The weight of the pitched roof didn't just push down on the walls. It also had a horizontal component and pushed sideways at the top of the wall. This pushed the walls sideways and they collapsed. One way to stop this was to shore them up using wedges of stone called buttresses. But these were regarded as ugly so hence the more elegant flying buttress. This is essentially a heavy column with a lot of mass. Then there is a half arch to the top of the wall. The idea is to turn the horizontal force into a vertical force in the way that an arch does. There are only a couple on Tewkesbury Abbey so these might be the remedial needed-to-fix-a-problem type.

Sluice causes stationary wave in Tewkesbury

The river was almost flooding after Storm Katie so the sluice must have been flat. The undulating wave pattern remained fixed as the water flowed through it. It's this aspect of stationary waves that has been the focus of my thinking recently. The pattern is stationary but the particle progress. Notice that turbulent flow follows.