More about the sea and reflections

We went to North Berwick on the Edinburgh coast. This picture shows the amazing Bass Rock on the right. They used to keep prisoners on it due to the ridiculously high sheer cliffs. The white top is actually due to big sea birds called gannets. What caught my attention was the strip of bright blue on the sea below the islands.

 

The blue strip is clearer on this picture. Notice that there is blue sky behind it.

In this last picture, there are clouds behind, and the sea isn't blue. I was thinking a lot at Easter about why the sea sometimes seems blue and I think that this day convinced me that a lot of it must be due to the reflection of blue light coming down from the sky. As noted in an earlier piece, it is the blue photons that are scattered in our direction by the atmosphere which is why the sky looks blue.

 

The next set of questions to answer will be to do with reflectivity. How much of the light falling on the sea is reflected? Some light must penetrate the water because it used by algae. How much of the light coming back off the surface of the sea has actually come from underwater and been refracted up to us? This must happen because in some places we can see the bottom of the sea or things submerged in the water.

 

Finally, if you've never been to Bass Rock, you must go. It is awesome!

 

Interesting clouds

This cloud formation caught my eye one evening. It was the fact that they were strung out into straight lines. I think that it is because the wind at that altitude was coming in from the left and dragging them along into lanes. Follow the link for a book that is an awesome introduction to clouds!

www.idareyoutoborrow.blogspot.co.uk  It's the April book that you want!

Feynman-fest on the iplayer

I had a great time watching two awesome programmes about Richard Feynman on BBC2 on Sunday night. He's my Physics Idol!

http://www.bbc.co.uk/iplayer/episode/p00zstkn/The_Challenger/

http://www.bbc.co.uk/iplayer/episode/p016d3kk/The_Fantastic_Mr_Feynman/

Pulsars

We went to St Bees Head on Friday night. As you can see, the weather was beautiful. The lighthouse reminded me of the work I've been doing on pulsars with the Upper Sixth.
Pulsars are neutron stars that spin very fast. They have beams of electromagnetic radiation firing out of their magnetic poles, each one like the beam of light from a lighthouse. If that beam crosses the path of the Earth, then the effect is the same as the flash of a lighthouse seen from out at sea. We detect a regular pulse of radiation, hence the name "pulsar". They were so regular that when first discovered they were thought to be alien signals. The story of their discovery and the controversy over the Nobel Prize that wasn't awarded to Jocelyn Bell Burnell. It's a story you should read. Her humility has impressed me when I've seen her interviewed.
Neutron stars are formed when a huge star runs out of fuel. Whilst they still have hydrogen, stars are able to do nuclear fusion in their cores. This sends out a stream of photons of light, creating a radiation pressure to counteract gravitational collapse. At the end of their lives, the lack of radiation pressure leads to collapse. In small stars like the Sun, the fact that you can only have a certain number of electrons on each energy level stops collapse.

This is called electron degeneracy pressure (look up Pauli's Exclusion Principle for the proper theory). In huge stars, even this can't withstand the collapse so the electrons are crushed into the nucleus. They join with protons, which cancels the positive charge on the proton to form a neutron. There's your neutron star - just made of neutrons, not atoms.
The strong magnetic field comes from the original star, though it is strengthened as the star gets smaller and the field lines are pulled in. One perceptive student noted that charged particles are needed for magnetic fields and that neutrons are not charged. I had to look that up - apparently there are still some unattached protons and electrons in the star.

A quarter peal on the bells

We rang a quarter peal on Wigton's bells on Sunday night. For the uninitiated, that means ringing non-stop for about 45 minutes whilst changing the order in which the bells sound every time you pull. Congratulations to our youngest ringer for achieving a first quarter peal.

 

It got me thinking about the physics behind the bells. Here's a picture of the bells that I took at Easter.

 

 

You'll notice that the bells are upside down. This is necessary because it allows us to control quite precisely when the bell sounds. It also makes the bells unstable. This is because it raises the centre of gravity whilst reducing the area at the bottom. My GCSE classes know that when the line of action downwards from the centre of gravity falls outside the base area, an object will fall.

You'll also notice that bells are designed to move in circles. In Physics, we say that the bell will have angular momentum. Now, linear momentum is a measure of how difficult it is to stop an object that is moving in a line. Linear momentum is calculated by inertial mass x speed. Angular momentum is how hard it is to stop something moving in a circle. Angular momentum = moment of inertia x angular speed. Moment of inertia is roughly a combination of how heavy and how far from the centre of turning. Think of ice skaters. They spin slowly with arms outstretched because they have mass further from their body. They have a large moment of inertia at this point. As they bring their arms in, they spin faster - in other words, a lower moment of inertia means that they have a higher angular speed. This is because they conserve angular momentum.

When I pull a bell, it swings in a circle until I stop the bell by holding the rope. The problem is that I can't stop the clapper, which still has angular momentum. It carries on until it hits the bell and stops.

 

I also thought you might like to see the view of Wigton from the top of the bell tower!

Liquid Nitrogen is Cool

We went to Penrith yesterday for an evening on Low Temperature Physics. We learned about how they get very close to absolute zero at Lancaster University. And then we got to see the liquid nitrogen demonstrations! In this first picture, there is a piece of dark coloured ceramic superconductor at the bottom in a bath of liquid nitrogen. There is a small magnet levitating over it. This is the Meissner Effect, where the superconductor expels the magnetic field. I need to do more research on this. It may be part of a later blog post.

 

Phil has been trying to make a maglev track. There is a clear Perspex track with magnets in it. Then he uses two ceramic superconductors in a bit of polystyrene cup, which is there to take the liquid nitrogen.

 

Now the superconductors are levitating above the magnet track.

 

And they still hang on when it is flipped upside down!

 

When I was in the Sixth Form, it was compulsory for someone to put a tie in liquid nitrogen and then snap it in half. I brought one from the minging tie cupboard. Trouble is that it absorbed too much liquid nitrogen and wouldn't freeze. Oh well.

 

 

The rest of the liquid nitrogen was tipped out in the grounds...cool!

 

Big thanks to Chris and Phil from Lancaster University for the talk and demos, and also to QEGS for hosting!