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.

Preparing for Lower Sixth Physics #10: Speed, velocity and relative velocity at Fort Dunlop

 

This is a view from the M6 driving through Birmingham. I remember Fort Dunlop from my childhood when it was a tyre factory. Now it is office space and hotel accommodation but it has always been an impressive building. The traffic was light and we were doing 70 mph. That was our SPEED. If I add in a direction and say we were doing 70 mph NORTH then I can call it my VELOCITY. Speed only has a size (a MAGNITUDE) but velocity has a MAGNITUDE and a DIRECTION. Speed is a SCALAR quantity (magnitude only) and velocity is a VECTOR quantity (magnitude and direction). So the red car on the other side of the road has a speed of 70 mph and a velocity of 70 mph south. You could say the velocity was -70 mph. Because the ground between us is closing up due to motion in both directions, it looks to me as though the red car is doing 140 mph. And it looks to the red car as if I am approaching at 140 mph. This is called the relative velocity.

Preparing for Lower Sixth Physics #9: Newton's Third Law

I did the water rocket today with three classes. The record stands at 93 metres. That's what you've got to beat next year. Anyway, it's an excuse to introduce Newton's Laws of Motion. There are three of them and you really need to know which is which. I'm going to work backwards and start with the Third Law. I learned it as "To every action, there is an equal and opposite reaction". In other words, we are talking about two different forces and they act on two different objects. Actually, that isn't clear in the statement I learned, so it has been rewritten as "If object A exerts a force on object B, then object B exerts a force on object A that is equal in size, acts in the opposite direction and is the same type." Applied here, the extra air pressure caused by pumping means that the bottle pushes the water down (the action). Thus the water pushes the bottle up (the reaction). Simples.

Preparing for Lower Sixth Physics #8: Internal resistance

I connected up this battery with a single wire. It's what we'd call a short circuit. The battery got quite hot after about 20 minutes. That's because electrical energy is being used up inside the battery and dissipated as thermal energy. The reason is because the inside of the battery has resistance - called INTERNAL RESISTANCE. When current flows, it dissipates thermal energy. So electrical energy is being wasted - that's energy that should have been going to components in the circuit. I posted previously about EMF, the amount of chemical energy transferred into electrical energy inside the battery. But since some of the electrical energy is wasted heating the battery, the actual output of the battery is less than the EMF. In fact, the higher the current that flows, the lower the output. (The output is called the TERMINAL pd because it is the potential difference between the terminal.) So although it tells you the EMF on the side of the battery, the actual output of the battery depends on what is connected into the circuit because this affects the current that flows.
DrPhysicsA on Youtube has been recommended to me. He covers the topic here: https://www.youtube.com/watch?v=8GNKgFB2T30&index=14&list=PL5D99A319E129A5B7

A moment of revelation

Here is a photograph that I took earlier in the year going over the pass of Drumochter on the A9 near Aviemore. It's the pylons that are going to be crucial here. I remember reading earlier in the year that the top central wire that runs over the pointy top of the pylon is the Earth. Yesterday I finally noticed that this wire is not supported on 1 metre thick insulators. It cannot therefore be at a high voltage. I can't believe that I have been looking at these all my life and never noticed. Always looking and never seeing!

Web resources for finding out about Simple Harmonic Motion

Here are some links to Khan Academy and Youtube videos:

https://www.khanacademy.org/science/physics/oscillatory-motion

http://www.youtube.com/watch?v=wb0qpWTkMJQ&edufilter=E4DB5UeAo7DC2VhYbnQDlw

There's also DrPhysicsA on Youtube. Lots of people tell me he's great!

https://www.youtube.com/watch?v=DVtyRt0CSSw&list=PL5D99A319E129A5B7

Preparing for Lower Sixth Physics #7: Electro-motive force

This cell contains chemicals that push electrons around a circuit. The ability to push electrons around a circuit is called the ELECTRO-MOTIVE FORCE or EMF. Yes it gets electrons in motion, but no it's not really a force. It's actually a potential (energy) and is measured in JOULES PER COULOMB (of charge). You'd know it better as VOLTAGE measured in VOLTS. Volts and Joules per Coulomb are the same thing. EMF isn't just any old voltage: In this case, EMF is the amount of chemical energy that is charged into electrical energy for one Coulomb of charge.

 

 

An optic fibre up my nose

Having taught Medical Physics this year, I got to experience it at first hand. The endoscope is the black fibre that goes diagonally from top right to bottom left across the middle of the picture. Part of that went a long way up my nose! An endoscope is made of two optic fibres. One runs from the box on the bottom of the trolley. The box contains a bright light source that strongly illuminates the tip of the fibre. That's so the inside of my nose is lit up. The other fibre runs back from the tip to the wider black section which is clearer in the top right of the photograph below. The doctor looks into this. The second fibre brings the reflected light back, which is the image of the inside of my nose. It must be lensed.

Preparing for Lower Sixth Physics #6: Factors affecting resistance

There are 3 factors affecting the resistance of an electrical cable.

1. The material from which it is made. This is called the RESISTIVITY. Gold has a particularly low resistivity but the cheapest alternative is copper.
2. The LENGTH of the cable. If you double the length, there is twice as much resistance. That's because electrons experience resistance when they crash into metal atoms. Double the length means twice as many atoms to hit.
3. The CROSS-SECTIONAL AREA of the wire. The wider the wire, the more space there is. More electrons can be sent down at once so the current is higher and we therefore say that the resistance is lower. Double the cross-sectional area means you halve the resistance.

So you really want short, wide copper wires.

Preparing for Lower Sixth Physics #5: Polarising light

Light is a TRANSVERSE WAVE which means that the vibration is at 90 degrees to the direction of propagation of the waves. In other words, when the wave goes forwards, the vibrations are from side to side. That means that the vibrations can have a preferred direction. They can all be up and down, or they can all be side to side. When they all vibrate in the same plane, they are said to be PLANE POLARISED. Sunlight is not polarised but reflected sunlight is polarised, provided you are looking at across the surface rather than down on it. My sunglasses are polarising filters. They will only let through light that is polarised in the right direction. In the picture of Glen Trool above, the left hand side is normal and the other two views are polarised in two different directions. The direction of the polarising sunglasses is shown below. The filter takes out some of the reflection in the middle picture making it clearer. The filter lines up with the polarisation direction in the right hand picture so all light gets through. None is filtered out so there is more glare.

Primitive science and a win for Germany

We had Dennis the Menace out for the World Cup Semi Final last night because Germany were playing in that kit. We found that when Dennis was stood next to the screen, Germany couldn't stop scoring. Someone moved him out of the way and the score stayed at 5-0 until we moved him back to the position shown. Then Germany scored two more. This is an example of a correlation. Putting Dennis next to the screen correlates with goals being scored. It is a scientific thing to notice patterns like this. But is this scientific? It can only be scientific if we can identify a CAUSAL LINK. In other words, if we can come up with a mechanism through which the position of a Dennis the Menace toy in northern England could influence the performance of the German football team in Brazil. There is no known link. Dennis was not the CAUSE. It's like the known correlation between the ability to read and shoe size in primary school. Big feet don't make you a better reader but older children will be better readers and their feet will have grown.

Preparing for Lower Sixth Physics #4: Stationary waves

Here's my guitar - as seen at Rock Night on Friday! Waves on the sea are called PROGRESSIVE WAVES because the peak (the crest of the wave) moves forward as time goes by. On a guitar, the peak stays in the same place but just goes up and down. The ends of the string are fixed so provided that the wavelength fits in perfectly, you get what is called a STATIONARY WAVE.

The conditions necessary to make a stationary waves are :

• Two waves travelling in opposite directions
• With the same frequency
• With the same speed
• With the same amplitude.

Here, the wave travelling in the opposite direction is made by the first wave reflecting back from ne of the fixed ends.

Players of stringed instruments will know that it is possible to play what are known as harmonics. Here, I gently placed one finger half way down the string to force that part of the string to be still (it's called a NODE). Then I plucked the string. The note was twice as high as the open string, with two vibrating sections. Technically, this second wave represents a full wavelength because a full wavelength has both a peak and a trough. The open string is only half a wavelength.

Radiation on the Cumbrian coast

I made a point to my class last week that people hear the word "radiation" in a negative, pejorative sense. But it just means energy that travels as rays. Normally that will be as waves, specifically electromagnetic rays, but it is also sometimes applied to beams of particles. So there is plenty of radiation in the picture I took at St Bees. The teapots are silver because that is a bad emitter of infra-red heat radiation. Bad emitter means that it does it, albeit slowly. So there is infra-red radiation in this picture. You can see the blue sky so there are photons of visible light. That could be described as radiation. I got a nice tan as well, so there must have been ultra-violet radiation. All in all, this radiation made for a lovely day out!

Cooling with liquid nitrogen

We were at Lancaster University for the Ogden Trust "Cumbria Young Physicist of the Year" Awards. If you're about to start the Lower Sixth, it could be you receiving an award next year! We were shown a trick with liquid nitrogen. Put in an empty water bottle and the liquid nitrogen is so cold that it will cool the air inside dramatically. Any water vapour and carbon dioxide freezes, hence the solid at the end of the bottle. Oxygen condenses at a higher temperature than nitrogen so you do get some liquid oxygen in the bottle. And the nitrogen gas is cooled so that it contracts. With fewer gas atoms inside the bottle and with those that there are inside moving slower, the pressure inside the bottle is reduced. Hence the air pressure outside pushing in compresses the bottle.

Preparing for Lower Sixth Physics #3: Superposition and interference

On this picture of Flodigarry Island off the coast of Skye, I have shown WAVEFRONTS in dotted yellow lines and RAYS as red arrows. They are PROGRESSIVE WAVES, moving from A down the picture. At first, the wavefronts are straight. These are called PLANE WAVES. The waves experience DIFFRACTION at the ends of the island and are transformed into semi-circular wavefronts. You now end up with two sets of wavefronts heading towards each other from opposite directions. They will overlap at B. This is called SUPERPOSITION. When this happens, you get INTERFERENCE between waves. If a peak of one wave meets the peak of the other wave, you get a single peak twice as high. This is called CONSTRUCTIVE INTERFERENCE. If the peak
of one wave meets the trough of the other wave, the waves totally cancel each other out. We call this DESTRUCTIVE INTERFERENCE.

Preparing for Lower Sixth Physics #2: Precision and percentage uncertainty

I've been making scones this morning which brings up the issue of making measurements. The two photographs below show the same reading. It raises an issue with needle meters. You have to get your head right over the needle to get the true reading. My head was slightly to one side in the first picture. That's called PARALLAX ERROR.

 I was reading the top scale which is in grams. The scales divisions are every 20 grams, so I say that the PRECISION = +/- 20 grams. In other words, I could be 20 grams either way. The reading is 40grams but there is some uncertainty because it's hard to be totally certain of the needle's position over the scale. Using technical terms, I say here that the UNCERTAINTY = PRECISION. So my reading is 40 +/- 20 grams and that my PERCENTAGE UNCERTAINTY = 20/40 X 100 = 50%. That's very high.
Advanced note: many physicists say that you can tell when the needle is half way between scale divisions so they say UNCERTAINTY = 1/2 x PRECISION. I've found it easier to teach classes the top version but this second statement is more accurate.

Look at the scale divisions on the left hand scale, which is in millilitres (ml). Scale divisions = +/-50ml, but they are very wide apart so we can claim a greater precision. The bubbles on the top of the milk don't help so I'd estimate my uncertainty as +/-20ml. Reading = 150 +/- 20ml which gives a percentage uncertainty = 20/150 x 100 = 13%.

Preparing for Lower Sixth Physics #1: Progressive waves

This is the first in a series of posts about topics for the Lower Sixth Physics course next year. Links to other resources were posted on Tuesday 24 June. Look them up!

Look at the 3 photographs above. They show the same wave as it breaks on Silloth beach. You can see that the peak of the wave moves from left to right. When that happens, we call it a PROGRESSIVE WAVE. It carries energy from one place to another.
There was a dispute about how to draw this on diagrams. The Dutch physicist Chritiaan Huygens drew lines along the peaks of the waves. These are called WAVEFRONTS. Isaac Newton wanted to show the forward motion of the waves, which is impossible to see in a still photograph, so he drew arrows to show the direction of motion. These are called RAYS. In the photograph below, the dotted red line shows the wavefront. It is what you normally think of and see. The yellow arrow shows the ray.

Adiabatic expansion and cloud over the Isle of Man

The weather forecast on the radio this morning said that there would be cumulus cloud forming in the cloudless sky once the temperature reached 18 degrees Celsius. I have not been able to chase up that reference. However we were walking on the Cumbria Coastal Path from St Bees to Seascale and noticed this cloud over the Isle of Man. It shows up better through a polarising filter. It will be because the land gets hotter than the sea (lower specific heat capacity - blogged about it before...) The air over the hot land expands, becomes less dense and rises. As it goes up, pressure is reduced so the air expands further for a different reason. The expanding air does work and so loses energy. The particles in the air have less kinetic energy and thus the air is at a lower temperature. This is the same reason why an aerosol deodorant feels cold. The process is called adiabatic because heat energy does not flow into or out of the air. The temperature is solely related to the kinetic energy of the molecules. Colder air holds less water vapour so it condenses out to form the cloud.