lab1a10 - Physics E-1a Expt 1: Measuring from a Distance...

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1 Physics E-1a Expt 1: Measuring from a Distance Fall 2010 Due Thursday, Sept 16, by 6 pm in your lab TA’s mailbox Introduction There are many objects in the universe that simply aren't easy to measure. You can not go out with a ruler and easily determine the radius of the Earth (although, it can be done!). Similarly, the size of the Moon is beyond the reach of your meter stick, and even the heights of the trees in the Yard are hard to sample with even the longest of tape measures. Since direct measurement isn't always possible, people have found indirect techniques for getting at various measurements. In this experiment, we will explore how an object's angular size can be used to determine its physical size, or its distance. Objectives The measurements for this experiment will not be performed in the lab. You will conduct them on your own (or with a partner), on your own time. We call this a “home experi- ment” and hope to accomplish the following: If you have been away from math for a while, this experiment will help you review the geometry and trigonometry. It will start you off on the right track concerning error analysis — learning to identify and deal with uncertainties in your measurements. You'll also get some practice in plotting data and extracting information from a graph. And finally, you will discover that it’s possible to measure seemingly difficult things with simple tools (this is the fun part). It’s actually pretty amazing what one can learn about our physical world using only the simplest of apparatus, good observations, and mathematics. Method The tool you will make is a quadrant. The quadrant uses the basic principles of surveying: that light travels in straight lines, and that some lengths and angles of a triangle (or other shape) can be measured so that unknown lengths, often not directly measurable, can be calculated. The simplest cases are (1) those in which one angle of a triangle is very “small,” or (2) one angle is 90˚. By “small” we mean that the angle (measured in radians) differs from its sine or tangent by so little that, for all practical purposes, these three quantities can be considered equal — this small angle approximation will be used in the moon measurement (and many times in this course throughout the year). Secondly, if one of the angles is 90˚, we simply apply the rules governing right triangles.
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2 Order of Tasks: First make your quadrant (page 10) and learn how to use it by measuring a window. Next measure the height of the Science Center with this new tool. Then, using only your arm, a piece of paper, and a ruler, measure the size of the moon. Please don’t leave the moon measurement until the last minute as the weather and/or phases of the moon may not cooperate with you. Finally, answer all the bold numbered questions on a separate paper with a few concise sentences. You will hand in these answers along with a copy of your graph from the procedure section (there is a check-list for this report on page 8). Quadrant
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This note was uploaded on 10/26/2011 for the course PHYSICS E-1a taught by Professor Wolfgangrueckner during the Fall '11 term at Harvard.

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lab1a10 - Physics E-1a Expt 1: Measuring from a Distance...

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