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> Castaway on a desert island Issue: 2013-3 Section: 14-16

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Have you ever thought about how you could survive in case you came to be a castaway n a desert island? While at 1st grade of Senior High School and in the context of our project, we decided to conduct some research concerning the question mentioned above, aiming not only at the acquisition of some basic knowledge around the subject, but also at the acquisition of some practical knowledge coming straight from the field of Physics. In order to make our study easier, we set the following sub-questions:


  • Weapon construction and ways of surviving
  • Orientation and castaway’s psychological state
  • Food, clothing, accommodation
  • Castaway’s communication


However, for the sake of saving time and space, we decided to present some indicative experiments of the previously mentioned sub-questions =>


  • Castaway’s orientation
  • Food ensurance
  • Water purification


A) Having in mind the goal of our research, which is the castaway’s survival, we thought that their orientation would play a very important role, because by knowing the points of the horizon, the castaway has the ability to ensure their escape from the island. So, in our search we managed to gather quite a few interesting tips for proper orientation using the help of the sun and the different constellations scattered around our galaxy. As regards the castaway’s orientation using the sun, they will first need to find the East-West axis. However, in order to do this, they will need to set a fixed position so they can observe the movement of the sun. This can happen by placing a straight tree branch or peg vertically on flat ground. Note, though, that the object which is intended for use is advisable to have a size that can create a satisfying shadow. So, the steps the castaway will have to follow, in order to spot the movement of the sun and with that the corresponding axis, are the following two:


  • Point 1, we mark the spot where the shadow is found
    We wait for some minutes so that the shadow moves for some centimeters (30-40cm)
  • Point 2, we mark the new spot where the shadow is found
    We link the two spots with a straight line and we have the East-West axis
  • Point 2 is the East and Point 1 is the West


In addition, in order to find where approximately the North is:


  • We place our right foot at Point 2 (east)
  • And our left foot at Point 1 (west)


As far as the moon is concerned, it follows the same course as the sun does, but it has a different orbit. So, by using the same logic, we can spot East and West and, after that North and South, making it equally useful for orientation. The sun and the moon differ at the point of the horizon where they appear according to each season, so the moon:


  • is found lower at the horizon during full-moon time in summer
  • is found higher at the horizon during full-moon time in winter


We can also make out in which state of its circle the moon currently is, this way:


  • It fills, if its enlightened side is on the right of its dark one, meaning that the enlightened side faces the one from which it is supposed to set. This also happens when the moon sets earlier than the sun (p)
  • It empties, if its enlightened side is on the left of its dark one, meaning that the enlightened side faces the one from which it is supposed to rise. This also happens when the rise of the moon happens after midnight (d)
  • This happens if we draw a conceivable line which passes from the conceivable edges of the moon, meaning that depending on which side each time the visible side is, the previously mentioned phenomenon is valid accordingly ( if “d” is formed, it gets empty, however, if “p” is formed it gets filled).

B) In order to ensure their food, which is the key element for a person’s survival, the castaway will have to resort to fishing, since he is in a place which can mainly offer him food sourcing from the sea. The castaway will probably have to use a pointed stick, which will help him catch a fish by throwing it. However, sometimes the castaway throws the stick, but realizes that he didn’t manage to catch anything. In this case, the science of Physics comes to the rescue by indicating to us the refraction of light. Physicians claim that when a thin beam of light falls onto the surface, on which two transparent and isotropic forms of different visual density are divided, at a certain angle, a part of this light is reflected, however, most of the light passes through the second form. The course of the beam on the second form is not a continuation of the original falling beam. It looks like that it gets broken upon the surface of the division and approaches or fends off from the conceivable vertical line that we set at the point on which the fall happened. This phenomenon is called R e f r a c t I o n.


Result of refraction

Ostensible elevation of objects. It is well known that objects which are placed inside pots including transparent liquid tend to look like they are on a higher level than they are in reality. The same happens also in the fish case explaining the reason why its catching was impossible.


C) In addition, the acquisition of drinkable water is considered to be necessary for the castaway’s survival. Even though the castaway is surrounded by water, which is also on a very large quantity, unfortunately, it is sea water, something which automatically makes it unsuitable for consumption. This is due to the fact that it contains iodine and a lot of different microorganisms. Consequently, its purification is necessary, otherwise the castaway will not manage to survive for a long period of time. After extensive research, we concluded that the most certain and guaranteed way for water purification is boiling it for approximately ten minutes. The ideal way of doing it so is by putting it over low burning fire for the longest possible time. One way or another, though, it is definitely a very time-consuming process, as the time needed to start the fire, boil the water and finally let it cool so the castaway can drink it is quite a lot. Eventually though, it is worth the effort.