Imploding drinks can

 We put about 1 cm of water into the bottom of an empty drink can. Well, it wasn't really empty; it was full of air. We boiled the water strongly so that steam was coming out of the can for nearly a minute. This drove the air out of the can and now we had a can full of steam. Then we quickly flipped the can upside down into the bowl with one smooth movement. It was important to land the opening of the can into the water. The water quickly cooled the steam down so that it condensed. In the liquid state the particles took up less space so now most of the inside of the can really was empty. It was a partial vacuum inside. The can collapsed inwards with a bang.

A can is normally fine because air particles on the inside pushing outwards are balanced by air particles on the outside pushing inwards. With a partial vacuum the air particles outside have nothing to balance their inward push. The can implodes.

Blue snow holes near Great Gable

 I stopped to look at the view and noticed that the post hole in the snow looked quite like it had blue light about 10cm down. I found this explanation  http://www.webexhibits.org/causesofcolor/5C.html  Some light penetrates the snow surface and travels downwards. It is scattered or absorbed by the ice crystals. Red and yellow are best absorbed. You can find a graph of it here http://www.webexhibits.org/causesofcolor/5B.html The blue is scattered and bounced around. That's what you see.

BBC Bitesize Revision for GCSE

Here's where you find Biology 1, Chemistry 1 and Biology 1
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/

Here's where you find Biology 2, Chemistry 2 and Physics 2
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/

Electrolysis of a molten salt

I worked in a fume cupboard to attempt the electrolysis of molten lead bromide. This photograph was taken through the glass window. It started out as a white powder and took a long time to melt. You can see that there is an orange gas in the beaker. This shows that bromine gas has been produced. It is a toxic gas - hence the fume cupboard. Bromide is a negative ion so is attracted to the anode. The lead is a positive ion and so is attracted to the cathode. The lead was hot when the electrodes were extracted from the beaker and soon turned from grey to yellow. I'm guessing that in the heat it had oxidised and the yellow was lead oxide. When it was all safe, I photographed the end:

The cathode was the right hand one. Perhaps that's a rim of lead.

Keswick flood defences and a centripetal force

I was interested that the flood defences were not an equal height all the way along. Surely the water will flow over the lowest bit... The answer is that the higher bit is on the bend. The water has inertia and would rather keep going in a straight line at constant speed. The bank has to push on the water to stop it going straight and push it round the bend. This force is a centripetal force. That's OK for the water that is actually touching the bank but water molecules aren't actually joined. Away from the edges there is little to stop the water layers sliding over each other and heading towards the edge. This means that at the bend the water level will be deeper on the outside than on the inside. Water is very hard to compress so there will be some form of rigidity lower down but the shear forces between layers to stop sliding will be weak.

Conservation of angular momentum: Christmas tea at Dobbies

We went for an early Christmas tea and I found a cheap spinning top in a cracker. I applied a torque to get it into motion. Angular momentum is the product of the angular velocity and the moment of inertia. Inertia is the property of mass that is resistance to changes in linear motion. But when rotated, the further away an equal sized mass is, the harder it is to change its motion. So moment of inertia is the integrated product of mass and distance from the centre. The top will slow down when friction causes a big enough torque to cause an appreciable rate of change of angular momentum. It did stop spinning in the end.

In an inertial frame of reference on Shap in the snow

 I was reading lecture notes about Special Relativity whilst being driven over Shap. It turns out that we were in an inertial frame of reference. Newton's First Law states that unless a resultant force acts, you stay doing what you are doing and have no acceleration ie you stay still if you were still and you carry on in a straight line at constant speed if you were moving. In other words, sitting still and being driven in a straight line at constant speed should feel the same and the laws of Physics should be the same. Our reindeer mascot was unmoved. He sat there as if at home. But if the brakes had been applied suddenly, it would have ceased to be an inertial frame of reference and the car would have stopped beneath him. We know that his momentum would have kept him moving forwards but it might have looked like he was "thrown" forwards. Only an external observer would know the truth but we in the car would have had to have invented a fictitious force to explain how it could seem normal and still have the reindeer moving around.

It actually looks like everything has stopped in the top photograph but if you look out of the side window, the picture is warped and you can tell you are moving. This is how you can tell if your inertial frame of reference is actually moving or not. And the view across to the snow-covered Coniston Fells was wonderful.

Dopper Effect Egret at Leighton Moss

This Great White Egret at Leighton Moss provided plenty of entertainment. I was interested in the circular ripples that emanated from its legs every time it moved. As it moved from left to right across the pond, the ripples started to bunch up in front of the bird and get spaced out behind. This is the same as the pattern I use in class:

In front of the movement the wavelength decreases and behind the wavelength increases. In front the frequency increases and behind it goes down. It's the old ambulance example: that the frequency of the siren is higher when it is coming towards to you and is lower than normal when it goes away. It is called the Doppler Effect.

New LED street lights

I photographed the new white street lights that they have been putting up around Wigton. I used a diffraction grating thinking they were mercury vapour lines and that I'd get an interesting emission spectrum. I got an almost continuous spectrum. It turns out that they are white LEDs. There are two spectra in the photograph above. The top one is the full Moon. The lower one is for the LED street light. Note that it has a gap between green and indigo/violet. If you look at the spectral intensity graph on this webpage, you'll see that we should expect a gap at about 500nm which seems about right http://rsos.royalsocietypublishing.org/content/2/8/150291

Positive curvature: summit of Great Gable

The summit of Great Gable was crowded for the act of remembrance on Sunday. It was good that so many people chose to attend. But it is a big summit and there was plenty of space. It is a dome-shaped summit. If you were given a long rope tied to the cairn and sent to walk a wide circle, the circumference would be less than 2 x pi x radius. The length of the rope would be the radius but because the summit drops away beneath you, the circle would be tighter than it would on flat ground. This is called a positively curved space. It is important in Einstein's General Theory of Relativity where mass warps space-time.

Is sap in trees affected by the Full Moon?

In his book Wildwood, Roger Deakin alleges that the Full Moon makes sap rise in trees. The logic is that the Moon is responsible for pulling the tide up so it should pull up sap. And that affects when to cut trees because you may or may not want them full of sap. This is said to affect whether they are likely to warp or not. But the Moon... the tides work by the Moon's gravity creating two maxima in the waters of the sea, one on the side nearest the Moon and the other on the opposite side. Effectively the Earth spins underneath this so high tide is when we move into the deeper water. Sap is not a free-moving liquid on the surface of the Earth so I'm skeptical. I'd need to know more about the dynamics of sap inside trees but logic would suggest that it should have two peaks in its height in the tree every day. I've not seen anyone suggest this.

The new energy approach: up Great Gable for Remembrance

We went to the top of Great Gable for the annual act of Remembrance. It is 100 years since the death of Siegfried Herford this year. He was one of the names read out. On the way there and back I was thinking a lot about the new way of teaching energy. Energy is held in stores. 8 possible stores have been identified. A start point and an end point are identified. Energy can move along one of 4 possible pathways to get from the start to the end. So climbing up the hill, I would say that I start with a chemical store and through the pathway of mechanical work that chemical store decreases and my gravitational store increases. I can also say that also by the thermal store in my body increases. This is probably through the heating by particles pathway.

Emission spectrum of a sodium street light

I took a photograph of an orange sodium street lamp through a diffraction grating. If you view a white light through a diffraction grating you see a full rainbow spectrum. In my picture, the street lamp is at the top of the picture and the spectrum is vertically below it. The yellowish blob is very prominent and that means it has a high intensity in this spectrum. But above it are smudges of green, turquoise and purple; below is a hint of red. All of these colours are separated by gaps. It is not a continuous spectrum. The lamps work by firing a beam of electrons through a thin sodium vapour. The electrons collide with the sodium atoms. This causes the electrons within the sodium atoms to gain energy and jump several electron levels. They fall back to their original level and emit photons of light as they do so. These are the colours that we see. Since there are fixed levels there are gaps in the colour scheme that we see. A better photograph is towards the bottom of this page http://www.chemistryland.com/CHM107Lab/Exp7/Spectroscope/Spectroscope.html

Sublimation of iodine

 At atmospheric pressure, iodine turns straight from a solid into a gas. This is called sublimation. I tried it out for the first time today. I put a few iodine crystals into a conical flask. There was a boiling tube of ice in the neck of the conical flask. This is called a "cold finger". I heated gently. The iodine sublimed into a purple gas. This then turned straight back into a solid when it hit the ice-cold glass. 

What I had forgotten was that this only works for iodine because melting and boiling are dependent on pressure as well as temperature. Look at this diagram for water https://en.wikipedia.org/wiki/Triple_point#/media/File:Phase_diagram_of_water.svg Normal air pressure is around 100 kPa, as shown by the red line on the diagram. If we dropped the pressure to 100 Pa then ice would turn straight into steam at about - 20 degrees Celsius. That sounds weird. But it is what the iodine has done. On the other hand, if we increased the pressure in the flask, then the iodine would melt into a liquid before boiling into a gas.

Perigee-syzygy Moon coming up on Monday

This is last month's supermoon. The full Moon on Monday will be even bigger apparently. The term "supermoon" comes from astrology. The Moon has an elliptical orbit around the Earth (oval!) so the Moon is not always the same distance from the Earth. Perigee is the name for the shortest distance between the Moon and the Earth on this oval orbit. Syzygy is the name for when the Sun, the Earth and the Moon are in line. This is true for a full Moon (but also for a new Moon). The thing I'm struggling with is that the perigee distance itself is quoted as a range, sometimes closer than at other times.

Year 13 Applied Science: Thickness of aluminium to stop beta

In this experiment, we first measured the background count because there is always this natural radioactivity in the air. We will never get a reading of zero. We got a reading of 16 counts in 20 seconds, a bit higher than normal because the lead-lined box containing the source was a bit too close. I then used 30cm tongs to get the source from the box and was careful to make sure that the source was pointing away from people. You were all over 2 metres behind the experiment and we have previously shown that our beta source cannot be distinguished from background at about 1.5 metres. Another safety precaution is to have the source out of the box for as little time as possible. We measured the count rate for the beta source through air. Then we measured the thickness of an aluminium sheet with a micrometer screw gauge. A reading of 40 means 0.40mm thick. We measured the count rate with 1 sheet, then added another and then a third. With the third sheet the count rate was down the background level, so we found that 3 x 0.40mm = 1.2mm of aluminium will stop all radiation from our beta source.

Year 12 Applied Science: Glycolysis reaction

This is elderberry wine on its way to completion. I added sugar to the elderberries and then added yeast. Yeast is a living things, a single-celled type of fungus. Like us it needs to do some form of respiration to turn its food into useable energy. Unlike us, it can only do a type of anaerobic respiration - respiration without oxygen. For yeast, the full reaction is called FERMENTATION.
However, it does involve the GLYCOLYSIS reaction in the CYTOPLASM of the cell that we have studied. Here it is...

The energy supply to start the reaction comes from ATP. This contains 3 phosphate groups but bonds are broken as it loses a phosphate group to become ADP. Breaking these bonds releases some energy and this energy is used to turn glucose into glucose phosphate, Glucose has SIX carbon atoms as does glucose phosphate. But then glucose phosphate splits into two TP molecules. Each TP molecule contains  only THREE carbon atoms.
Each TP molecule now needs to turn into pyruvate. To do so, it needs to lose a hydrogen and a phosphate. Bonds are broken so the TP loses energy. That energy has to go somewhere. It is used up turning ADP back into ATP. And the NAD+ mops up the spare hydrogen atom.
We can get away with saying that ATP is high energy and ADP is low energy. Going from ATP to ADP releases energy. Going from ADP to ATP needs energy. Overall glycolysis makes more ATP than it uses up. So the cell ends up with more high energy ATP than it had at the start. So we say that the cell has gained energy from the breaking up of glucose into two pyruvate molecules.

Custard/corn flour with water is not thixotropic

 We added water to a custard/corn flour mix. Above, it was flowing freely. Then we tried to stir it (below). It became solid and the stirrer wouldn't move.

I confidently told my class that the mixture is thixotropic. But apparently it isn't http://www.thenakedscientists.com/forum/index.php?topic=3697.5;wap2 It is similar but undergoes shear thickening instead. I'd never heard of this. Here's what I found https://en.wikipedia.org/wiki/Dilatant The custard mixture is essentially a suspension - ie tiny solid particles floating in water. Applying a shear stress (that's basically a tearing force) the particles get pushed close enough together that instead of electrostatic repulsion, they start to attract each other using forces called Hamaker forces. I've come across Van der Waals forces before where a negative charge on one particle repels electrons to the far side of the neighbouring particle, leaving the near side positive so that - hey presto! - they attract. Hamaker forces are this done with bigger particles. The particles in the suspension are pushed close enough together for this to happen and that grabs the particles into to order to be like a solid.

Total Internal Reflection: DVD player

I was interested to find out that the indicator LEDs for the DVD player were actually some way down under the display, soldered to the main circuit board. Light is taken up and along to the front of the display by some solid chunks of clear plastic. The light goes vertically up and then hits the outer slanted edge of the plastic. The angle of incidence will be 45 degrees. If the refractive index is the right size then the critical angle will be lower than 45 degrees so the light will reflect. Angle of reflection will be 45 degrees meaning the light is bent through 90 degrees and exits horizontally. The bigger semi-transparent window is to allow infra-red from the remote control to be detected by the sensor on the circuit board.

Centre of mass of the UK

 To find the centre of mass of an irregularly shaped object, you hang it so that it can swing freely and let it settle under gravity. There is then a plumb line hanging down from the suspension point. Draw a line vertically down the plumb line. Repeat for a different suspension point. Where the lines cross, that is the centre of mass. So the centre of mass lies directly below the suspension point.

 The reason is shown below. If I pull the object to the left side and out of equilibrium, there is more weight on the left of the plumb line that on the right. Each of the two divided sections of weight are act as a turning force (a moment). The moment on the left is an anti-clockwise moment, The moment on the right is a clockwise moment. But the anti-clockwise moment is bigger so there is a resultant moment pulling the shape back down. There is no resultant moment when equal weights are on either side of the plumb line. That can only happen when the centre of mass is below the suspension point.

If you suspend the object through the centre of mass, there will always be equal weights on either side of the middle. You can swing it to any position and it will stay there. There will never be a resultant moment.

Finishing the birthday balloon calculations

I modeled the balloon as a flattened cylinder. I calculated the volume as 0.0113 cubic metres. Air has a density of about 1.2 kg per cubic metre so mass of air displaced = 0.0135kg of air displaced so upthrust = 0.135N. Density of helium is 0.164 kg per cubic metre so there is 0.002kg of helium in the balloon. But the foil weighs something too. I calculated the surface area of the balloon as 0.301 square metres. I looked for possible thicknesses of foil on the Internet and came up with 0.03mm. Density of aluminium is 2700 kg per cubic metre giving the mass of the foil as 0.024kg. Weight of the balloon = 0.26N ie more than the upthrust so the balloon shouldn't float. The thickness must be wrong. On yesterday's post, I think the derivation of the equation was correct, so I stuck with the measured time period of 7 seconds and worked backwards to a thickness. It came out as foil of thickness 0.014mm. That doesn't sound impossible.

Birthday balloon simple harmonic motion analysis

The first part of the document below shows how I do an SHM analysis for a pendulum. The restorative force pulling it back to equilibrium acts along the radius of the motion so perpendicular to the string. This means that no component of tension is involved, The resultant force turns out to be the sine component of the weight mg. But sin(theta) = x/L. For small angles x is approximately equal to the true displacement.

The balloon analysis takes up the bottom two thirds of the page. It works in much the same way except that two forces act on the balloon vertically - the upthrust and the weight. I have turned them into a resultant F. Hence the intertial mass m does not cancel this time although the solution as the same form. I got a theoretical answer of 1,1 seconds having measured it as 7 seconds. I will post later about how I got estimates for the upthrust and mass.

Birthday balloon pendulum

I received a helium balloon on my birthday! I found that it had a very damped oscillatory motion. I counted 5 cycles in 35 seconds. This was an occasion on which I should have used a fiducial marker. This is an indicator of the centre of the oscillation. Oscillations are timed from the fiducial marker. This is because the object is moving fastest at that point. I timed from the amplitude. That seems better but the problem then is judging the exact time at which it stops moving and turns to go back. With fast oscillations there is little difference but with slow oscillations using a fiducial marker is more accurate. So for my balloon, one time period = 7 seconds. For a normal pendulum, time period T = 2pi x square root (L/g). So if this equation applied to the balloon, L=T squared x g / 4 x pi squared, which comes to 12.4 metres. The string was less than 2 metres long so the normal pendulum equation does not apply.