College Physics

Essay by PaperNerd ContributorCollege, Undergraduate November 2001

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The problem given to our class was to make a device that can measure latitude and longitude of a previously unknown place. After working on this project continuously, for about two weeks, we came up with an answer to this problem. We designed two different apparatuses, one for measuring latitude and the other for measuring longitude.

To measure longitude, we made a "simple sundial". In order for us to do that, we had to use a straight stick, a ruler, and a flat piece of wood.

It is also very important that we find a level piece of land, because otherwise our longitude might be a few degrees off.

Next, we need to figure out what time the shadow of the stick will be shortest. To do this we will record the shadow's length every five minutes, each time recording the time that we checked the shadow. When we see that the shadow is starting to get longer, we know that we had already recorded the length of its shortest point, or the time of local solar noon, and we have recorded the time when the shadow began to get longer.

Now is when we need to use an equation to figure out the longitude of a certain place. We already know that the earth rotates about 15 degrees per hour. We also know that there is a five hour difference between the Prime Meridian and the United States. Therefore, we need to multiply fifteen times five, which equals 75.

Then we take the time that the shadow was shortest and subtract it from the time that the shadow began to get longer. For example, if we went outside at 12:00 and recorded the length of the shadow to be 36 inches long, and within the next ten minutes the shadow was 38 inches long, we know that we have just reached local noon time. So, we would then take the difference in the two times (12:10 minus 12:00 equals ten minutes) and multiply 10 times .25 of a degree, because the earth rotates ¼ a degree per minute. Then we add or subtract the total by 75 degrees to find our longitude. If we go out before noon, we subtract 75 degrees, and if we go out after noon we add 75 degrees.