Physics Special Topics

Highlights of Physics Special Topics Vol.13

Volume 13 (2014/15) of the University of Leicester Journal of Physics Special Topics is now complete. This year, ten groups of students published 67 short papers covering a subjects from Hunting for monopoles, to Noah's ark: the story continues.... 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.

Or read about the educational purpose of the Journal.

PST in the media

Humans Barred from Mars by Greenhouse Effect

W.H.A. Longman, Kieran Flatt,Sam Turnpenney, Maria Garreffa

Following recent claims by both Paypal entrepreneur Elon Musk and NASA, students at the University of Leicester have investigated the possibility of moving the human race to Mars.

Many problems associated with extra-terrestrial colonisation occur due to the difference between the atmosphere on Earth and the target planet. The human body has evolved to be able to survive within the range of temperatures and pressures commonly found on Earth and significant deviation from this range would be very dangerous.

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Chief scientist Alex Longman investigated the possibility of moving the human race to Mars.
One way to avoid this issue is to alter the properties of the Martian atmosphere so that they are more similar to Earth. Geoengineering is a hot topic in the media recently, with a variety of large scale projects being put forward to tackle the problem of anthropological climate change. Students at the university have investigated the technique of inverting the process that has causes problems on Earth: burning coal on Mars to release CO2 into the atmosphere. It was hoped that this would lead to the greenhouse effect occurring, heating the planet and leading to a friendlier climate.

Unfortunately, the students found that such a method is not realistic. The amount of coal needed would be so great that over 2000 trillion trips would be required to transport it to the Martian surface, using the best currently available rocket technology.

Alex Longman, a student at the university who worked on this project, said: “Climate change is one of the biggest problems facing our generation, and it is vital that we have long term plans in place.

“We have found that it’s unlikely we’ll be moving to Mars soon. This shows the importance of taking care of our own planet and acting today!”

The paper ‘Terraforming Mars: CO2 Combustion’ can be read here: http://physics.le.ac.uk/journals/index.php/pst/article/view/749.

 

Harnessing the power of rain

Jeremy Hue, Rob Miller, Chris Checklin, James Farrow

Physicists at the University of Leicester have found a way to harness energy from falling rain, but does it stack up to solar energy?

Using a method similar to that used in hydroelectric dams, it was determined that a large container placed high above the ground collecting rain could then use the falling of the water to power turbines. Because clouds gather water from large areas (25 times the size of the cloud), the scientists predicted that sufficient water could fall into the container so that a large amount of energy could be produced.

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source: http://upload.wikimedia.org/wikipedia/commons/0/03/Srisailam-dam-with-gates-open-2.jpg
They worked out the amount of water falling over a given area and used this to calculate how much energy would be generated by this rainfall. It was discovered that the amount of energy created using the container depends on its altitude. The scientists then compared the amount of energy produced using this method to the energy that could be harvested by solar panels of the same area.

The group of researchers found that solar panels are a thousand times more efficient than an identical container placed on the ground. However, they also found that if the container was elevated by 1km then the same amount of energy could be obtained.

Lead author, Jeremy Hue stated “After extensive research it has been determined that constructing a container that high off the ground is currently not economically viable, especially when compared to the cost of covering the same area in photovoltaic cells.”

He added, “As solar cells become more efficient and cheaper as technology improves these may become the status-quo for renewable energy in the future; however, we should not close ourselves off to innovation.”

The full text can be read at https://physics.le.ac.uk/journals/index.php/pst/article/view/776

Wings of mythic proportions; were the wings of Pegasus really
large enough?

T. Bradley, L. Garland, G. Mcquade and M. Walker

The mythological winged horse Pegasus is seen in popular films and literature such as Hercules. In an article by a group of physics students from the University of Leicester, a minimum size of its wings are calculated.

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Image source; http://disney-clipart.com/Hercules/Hercules-Pegasus.php
If Pegasus were the same size and weight as a regular horse, it is found that a smallest individual wing size of roughly eight meters squared is needed for flight. If the wings are the same width as Pegasus' body length (roughly 1.5m) this would give a tip to tip wing-span longer than a double decker bus. Clearly in popular fiction Pegasus is not shown with such a large wing-span.

These results were found using a simplified model of flight involving the use of a ratio known as the Strouhal number. This relates the speed at which a wing flaps to the flight speed and the height the wings reach. It was found in a separate study that all flying animals have a Strouhal number between 0.2 and 0.4.

Thomas Bradley, lead author of the article adds, "Though a surface area is calculated in this paper, due to the simplification of the physics involved it is highly debatable whether the value is accurate or reliable." The results found in this article would be interesting to consider in the use of Pegasus in popular fiction. For example, in Disney's Hercules, Pegasus would need to go on a growth spurt to actually fly.

The full text can be found at https://physics.le.ac.uk/journals/index.php/pst/article/view/781/572

 

It’s not just smoke and mirrors

Alexander Foden, Adam Higgins, Claire Sullivan, Jonathan Sallabank

Magicians have been fooling audiences for centuries. From sawing women in half, to pulling rabbits out of hats, everything seems to be possible. From the vast pool of tricks magicians have though, one seems to be repeated more than any other. Floating. This one trick always seems to leave audiences asking “How did that happen?” This is exactly what a group of students at the University of Leicester have asked. They came to the conclusion, “It’s not wires. Probably.”

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Magician Chris Angel, floating
Obviously, magicians don’t generally tell how their tricks are done, but this doesn’t stop people guessing. One of the more popular ideas is that wires, too thin to be seen, are used; this was put to the test by 4 final year physics students at the University of Leicester. Their paper called “It’s not just smoke and mirrors” appears in the University’s publication, the Journal of Physics Special Topics .

The students looked at two situations, one where only one wire was used, and another where two were used. After some number crunching, they said that all of the wires we currently know about would break under the weight of an average person.

It’s not all doom and gloom though. The students say that other combinations of wires could potentially be used. They even suggest that there may be ways to camouflage the wires.

This means that magicians can rest at ease knowing their secrets are still safe. And if someone says they used wires, they can point them in the direction of this paper.

The paper is available from https://physics.le.ac.uk/journals/index.php/pst/article/view/780

Going against the masses: how the ship from Interstellar survives the event horizon

Jordan Iain Penney, Giles Christopher Lipscombe, Roger Paul Leyser, Hayley Jane Allison

After the recent (2014) release of the film ‘Interstellar’, there has been much debate about whether the spaceship, Endurance, would have been able to survive passing through the event horizon of a supermassive black hole. Many sources have claimed that this is an error in the film, but a group of physics students from the University of Leicester have shown this not to be the case.

The event horizon is the distance from a black hole where you cannot escape the pull of its gravity; anything within this horizon is trapped forever. Many argue that beyond this point, the spacecraft would have been destroyed by the large stretching forces of the black hole. However, for supermassive black holes, this effect occurs much further in, past the event horizon. The spaceship would, therefore, have to get far closer to feel any large effect.

By looking at the forces involved, the distance from the black hole at which the Endurance would be torn apart was found. This is the point where the forces keeping the ship together would be overcome by the pull of gravity. For the black hole which is a hundred million times the mass of the Sun, the students found this to be 3 billion metres, one fiftieth of the distance between the Sun and Earth. This is around one hundredth of the radius of the event horizon for the black hole in the film.

For the scene shown in the film Interstellar, the students conclude that the ship would be able to travel well within the event horizon before being torn apart. The film and its science advisor, Professor Kip Thorne, were therefore correct.

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Source: http://imgur.com/ydnkSuP.jpg

The full text of the paper can be read at https://physics.le.ac.uk/journals/index.php/pst/article/view/772

 

The positives of global warming: satellite orbital decay

Christian Michelbach, Luke Holmes, Dan Treacher

In response to an in-house discussion at the University of Leicester about the problem of global warming, a group of students have written a paper about the effects of global warming on spacecraft in low Earth orbit (LEO). This work was produced by fourth year students and can be found in the Journal of Physics Special Topics which is available to the public.

This study shows that once molecular effects are considered, contrary to first impression, global warming will not increase the rate at which a space craft deorbits.

p1-2014This means that although global warming is a large problem for mankind, it will take less energy to keep satellites in orbit. This means that they can stay in orbit for longer with the same amounts of fuel. Some examples of craft that would be affected by this change include: ISS, HST, and other Earth observation satellites. This allows the craft a longer operational lifetime which in turn produces more useful data.

A typical simple model of global warming assumes the atmosphere is an ideal gas (a gas where interactions between molecules can be neglected). This new paper however also shows how the addition of CO2 changes this model to include the consequences of CO2 higher mass than the air average and how the behaviour of CO2 at low densities governs the orbital decay of satellites.

The full text can be read at https://physics.le.ac.uk/journals/index.php/pst/article/view/753

 

The Skywalker twins drift apart

Thomas Griffiths, Duleep Vasudevan, Katie Herlingshaw, Mark Phillips

Physics students at the University of Leicester have concluded that in the film Star Wars Episode V: The Empire Strikes Back, twins Leia and Luke Skywalker do not actually remain the same age. This is due to relative velocity time dilation (Einstein’s theory of relativity) which results in time ticking more slowly on an object that is moving at a higher speed.

The calculations made were based on the twins’ journeys to Cloud City.  Leia travels from the neighbouring system of Anoat, while Luke travels from the much more distant planet Dagobah. Luke’s journey was estimated to be 25 times longer than Leia’s.

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http://images4.fanpop.com/image/photos/24000000/Anakin-Padme-Luke-and-Leia-the-skywalker-family-24022920-1024-768.jpg
Additionally, as Leia travels in the Millennium Falcon, a much larger ship with more powerful engines than Luke’s X-Wing Starfighter, it was assumed that it reaches a higher speed. Leia’s journey yields a time dilation of 62.6 days however Luke experiences a time dilation of 700.8 days (1.92 years). Duleep Vasudevan, Tom Griffiths, Mark Phillips and Katie Herlingshaw found that Luke is therefore 1.75 years younger than Leia.

In the second scenario gravitational time dilation (slowing of time due to gravity) is considered. Cloud City, a mining station, floats above the clouds of the planet Bespin, a gas giant very similar to Jupiter. An observer at a distance far from the planet would see time pass more quickly than an observer on the surface.

The lead author Thomas Griffiths says “For Luke to become the same age as Leia he would have to orbit the gas giant for 9.77 million years.”

The paper, The Skywalker twins drift apart, can be read at https://physics.le.ac.uk/journals/index.php/pst/article/view/716

 

Would you like some tea?

Poonam Patel, Jessica Patel and Rutambhara Joshi

p3-2014Three physics students from the University of Leicester investigated the cooling rate of stirring a cup of tea, in comparison to leaving tea to cool by itself. By making reasonable assumptions such as only considering the heat loss from the top of the mug, Poonam Patel, Rutambhara Joshi and Jessica Patel were able to calculate the change in surface area caused by the stirring motion.

The rate at which tea cools is proportional to the surface area and the change in temperature. Due to the rotation of the fluid, caused by the stirring, a larger surface area is created from which further heat loss can occur. As a result a higher cooling rate was determined for stirred tea.

The students found that stirred tea cools faster than tea left alone, by a factor of 0.06, assuming an average of 100 rotations per minute. Lead author, Poonam Patel, said “Given the lack of time people are often faced with, the small change in the cooling rate would be negligible”.

The paper can be found at: https://physics.le.ac.uk/journals/index.php/pst/article/view/767

The Lunar Recession

Lawrence Evans, Daniel Cherrie, Adam Tyler, Luke Ingram

Many people are unaware that the Moon’s orbit around the Earth is not fixed. Instead, the Moon is currently receding at a rate of about 3.8 cm per year, which although small will have important implications for us in the future.

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Credit: NASA
Fourth year physics students at the University of Leicester calculated the distance at which the Moon will no longer recede from us, orbiting at the same rate as the Earth’s own rotation, which will have slowed down considerably. The students found that the Moon would orbit at a distance of around 558,000 km away, compared to the current Earth-Moon distance of about 384,000 km. When this occurs, the physicists calculated that a day on Earth would be about 48 current days long. This means the Earth would be rotating about 48 times slower than today! Consequently, the Earth would also absorb more thermal energy from the Sun in each ‘day’.

The Earth and the Moon influence their own rotation rates by tidal interactions. The Moon raises tidal bulges on the Earth due to gravitational attraction and the inertia of the rotating Earth, but since the Earth is currently rotating much faster than the Moon orbits, the bulges slightly lead the Moon. Hence, the Moon exerts a braking torque on the bulges, effectively slowing the Earth’s rotation, and consequently accelerating the Moon into a larger orbit. The fact that the Moon is receding, and the Earth’s rotation is slowing, is also a consequence of the conservation of angular momentum. The Earth will continue to impart angular momentum to the Moon until they both reach a common angular velocity.  To an observer on Earth at this time, this will result in the illusion that the Moon is fixed in the sky.

The paper argues that based on the current recession rate of 3.8 cm per year, this situation will occur in about 4.6 billion years time, by which point the Earth may already be uninhabitable due the Sun expanding as it ages, into a red giant.

The paper can be found at: https://physics.le.ac.uk/journals/index.php/pst/article/view/778

Laser Controlled Lightning!

Sabahuddin Humayun, Francis Davies, Ben Woodward

p5-2014Physics students at the University of Leicester have investigated the possibility of inducing, directing and controlling lightning strikes using lasers. In their paper titled “Light-ning Rod”, Ben Woodward, Francis Davies and Sabahuddin Humayun have proposed the possibility of using high powered laser beams as lightning conductors. These lasers could artificially trigger lightning during a thunderstorm before it naturally strikes.

They discuss how air can be ionised using lasers in order to provide a conducting path for a lighting strike. The fact that lightning, like any other form of electricity, will always follow a path of least resistance is used to control where and when it will strike. Lasers are used to ionise air tracks which are used as the path of least resistance.

By this method, lightning strikes can be induced at a desired time, along a desired path before their natural occurrence. This approach could save many lives, money in potential repairs and the power of lightning bolts could then be harnessed for other purposes.

The students concluded that current technology is fully capable of achieving this feat. However, this approach would be highly impractical due to requirements only met by laboratory grade lasers which are extremely expensive and enormous in size and maintenance needs.

The full text of the paper can be found at: https://physics.le.ac.uk/journals/index.php/pst/article/view/711

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