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# Physics Special Topics

#### Highlights of Physics Special Topics Vol.13

Volume 14 (2015/16) of the University of Leicester Journal of Physics Special Topics is now complete. This year, six groups of students published 51 short papers covering a subjects from The power of Norman England, to Cinderella's shattered dreams. The full journal can be accessed at physics.le.ac.uk/journals/index.php/pst

This year each group of students selected their own 'highlight'. Take a look below.

PST in the media

### Fantastic Post and How to Deliver it

A. R. Fogg, A. L. Bentley, L. J. Holdsworth, E. I. Spender

Thinking of training your Owl to deliver post? A group of physics students at the University of Leicester have looked into the possibility of an Owl Post system like that featured in the Harry Potter stories. Throughout the films witches and wizards are delivered mail items of all shapes and sizes, from small letters to broomsticks. In fact, Harry was delivered a Nimbus 2000 in Harry Potter and the Philosopher’s Stone.

One of the most important things to consider in this study was the aerodynamic forces on the wing of a Snowy Owl. The balance of these forces decides whether the bird is able to fly. The Balance between the lift on the Owl’s wing and the combined weight of the Owl and its package was considered as the most important condition deciding whether the bird could fly carrying the load. The authors studied in depth the delivery of a Nimbus 2000 to Harry in the first story.

First, the mass of the broomstick was estimated to be about 3kg. Using this and the mass of a Snowy Owl of about 2kg, it was found that the Owl-package system had to be as aerodynamic as a military jet. This is very unlikely.

To further this study, the authors studied if there was a trend between the size of the wing of the bird and how aerodynamic it needed to be to carry the broom. As expected, it was found that to carry the broomstick, the bird needed to be either very large wings, or small wings that are very aerodynamic.

Lead author Alexandra Fogg stated, “In this project we made lots of simplifications to the idea in order to come to our results. However it seems from the physics that Owls would be able to carry lighter loads, such as letters and small parcels. So don’t worry, you can still get your Hogwarts acceptance letter by Owl Post.”

### The Explosive Secret of Iceman’s Powers

A.B.S. Stirton, E.C.A. Golightly, S. Kent, O. Brennan

Physics students at The University of Leicester have investigated the science behind the superhero ‘Iceman’ and found his powers to not be so cool after all.

Superheroes have long been in the public imagination as figures of inspiration and entertainment, many of these heroes have origin stories that pay lip-service to actual science, the X-men for instance take a very loose interpretation of genetics to give their heroes incredible powers, one such hero is Iceman. Iceman has the power to manipulate, surprise surprise, ice. This includes freezing water in the air around him into ice-constructs and even freezing his own body into solid ice. To do such a thing Iceman would need to expel a large amount of energy to rapidly freeze the water around him into ice.

Water freezes when the surrounding environment is cold enough that the energy from the water flows into the colder surroundings, this is due to the second law of thermodynamics: ‘Energy will always flow from a hotter object to a colder object.’ Normally when water freezes it does so quite gradually, over a period of hours or minutes, giving the energy time to spread out evenly into the surrounding air. When Iceman freezes himself he does so in a fraction of a second, this gives the energy flowing out of the water almost no time to spread evenly and instead it builds up next to Iceman, this causes the temperature around him to rapidly increase until it is about 41000 degrees Kelvin, eight times hotter than the Sun! This would have an opposite effect to what our hero’s name suggests and would instead create an explosion similar to a nuclear bomb, albeit at a much smaller scale.

### Superman reverses the Earth's spin

Bhalraj Singh Chima, Brady Marc Lloyd, Nathan Wall, Karl Tassenberg

University of Leicester students find how fast Superman would need to travel around the Earth to reverse its spin direction. It was assumed that he travels around the equator. In the film, Superman flies around the Earth for 50 seconds. With that, the theory of relativity is used here as well as moment of inertia and angular velocities of the system. Hence, it was found that Superman's mass needed to be at least 13.7 million times his normal mass with a speed that is really close to the speed of light.

The impact this has on life on Earth would be the chance of extinction because total mass (and gravity) of the Earth and Superman would now be much larger than if only the Earth was taken to account. Therefore, this system would attract a larger amount of objects towards Earth. The force felt by the Moon would be small because the extra mass of Superman is not enough to effect the Moon whose distance is so far away. So, it is safe to assume that the Moon doesn't collide with Earth but draws nearer by a very small amount.

On the other hand, another danger to life on Earth would be the increase in wind speed at the surface of Earth. This is because the momentum is transferred directly to the Earth but not the atmosphere, which seems likely due the spherically symmetric nature of the atmosphere. This means that the polarity of the Earth changes quickly but the atmosphere will suffer no change, so the speed of the winds might be as large as twice the spin of Earth, 930m/s. The strong winds can lead to hurricanes and tornadoes which will be a risk to life.

### Is the universe fine-tuned for origami?

Jack Stephen Baker, Raif Norisam, Kai Wright, Tom Buggey

“How many times can you fold a piece of paper?” thought Britney Gallivan to herself in her high-school mathematics class.  At the time, the maximum number of folds of a piece of paper was thought to be seven or eight. She later proved this to be incorrect, proving that the maximum number of folds was indeed eleven. However, Gallivan’s method for finding the maximum number of folds could be applied to any flat surface. Hence, students at the University of Leicester calculated the number of folds possible in the universe at any time.

In 1929, Edwin Hubble observed that we live in an expanding universe and that the rate of expansion is increasing. Consequently the size of the universe is limited at any time, to a distance known as the Hubble distance. This means that the size of the piece of paper is fixed to this maximum distance.

Students considered a piece of paper equal to the Hubble distance in size, with width 0.1mm. They found that the maximum number of folds for such a piece of paper is sixty seven.

The graph (right) clearly shows that, in recent years, the number of folds possible of such a piece of paper has increased significantly up to the present day. We can also see that, in future years, the number of folds possible will never increase beyond approximately sixty seven. Raif Norisam, student at the University of Leicester, commented that ‘the results are incredible, we are at a unique time in the universe where we can fold a piece of paper more times than we ever will!’

### The draining of a lifetime

Makita Sadhra, H. Samaratunga, H. S. Ahmed, Laura Tonks

Throughout human history there have been tales of blood drinking vampires. Students Makita Sadhra, Harindu Samaratunga, Hibo Sheikh Ahmed and Laura Tonks from the Department of Physics and Astronomy have worked out that it would take 6.4 minutes for a vampire to drain 15% of blood from a human’s body, in a paper for the Physics Special Topics module “The Draining of a Lifetime”.

Vampires are mythical creatures who feed on the blood of humans, however it was found that only 15% of a human’s blood can be taken before major effects on the circulatory system occur. The students modelled the aorta and carotid arteries as smooth tubes to use fluid dynamics to calculate the time taken.

The vampire drinks the blood out of the external carotid artery which connects to the common carotid artery which comes from the aorta. The students used the continuity equation and the Bernoulli equation to calculate velocities of blood flowing through the arteries in their model, to ultimately find the volumetric flow rate which allowed the time taken to be calculated. It was concluded that a total time of 6.4 minutes was taken for 0.75 litres of blood to be lost through the external carotid artery, which tells us that should a vampire exist it would not be able to make such a quick escape as seen in the popular TV series “The Vampire Diaries”

### ‘Orbital Death Laser’ Could Be Built

Laura Katey Wharton, John Alexander Paice, Riddhi Sankdecha, Samuel James Wharton, Anuti Joshi

It turns out that 007 films might not be as far from reality as you might think. Masters students at the University of Leicester have found that satellites – such as Icarus from 007’s Die Another Day, capable of burning through the atmosphere and vaporising anything on the Earth in its path – could indeed be possible without much more technological development.

The doomsday-predicting students found that, in order for it to cut through metal, a space-based laser would have to gather over six million watts of power from sunlight. Using the best technology available today, the area needed for the solar panels was found to be only a little larger than that of a football pitch. A laser of this size could easily cut through metal sheets – let alone any intrepid secret agents – with ease.

“You could say it’s a ground-burning revelation”, said the student in charge of the investigation.

In the film Die Another Day, the Icarus Satellite demonstrates immense power as it carves a path through the ground, as well as cutting through the aircraft that James Bond uses to escape from the path of the beam.

The solar panels required would be too large to launch in one piece, but could be launched in stages and then built in space. If built it is theoretically possible that the laser could strike anywhere on Earth.

“Science has always been a tool for advancement and discovery”, said another of the students on the team, “but we must always be wary of it being used maliciously. Using such a weapon would be as easy as flicking a switch.”

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