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1.6: Activity 1E - Measurements in Geology

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    Observations and measurements are used in all the sciences. An observation is information obtained directly from one of the five human senses. A measurement is a means of expressing an observation with great accuracy. Measurements are expressed by both a numerical value and a unit. It is critically important to always ensure your number has a unit! In the US, we use two systems to measure: the English or Imperial System and the Metric or International System (SI). Typically, scientists will utilize the metric (SI) system for consistency.

    Common geologic measurements

    • Length: the distance between two points
    • Mass: the amount of matter in an object
    • Time: the duration of the event being observed
    • Temperature: a measure of kinetic energy, commonly known as heat.

    If you are unfamiliar with measurement abbreviations, the following tables may be a helpful reference.

    Table 1.1: Abbreviations for common Imperial and Metric measurements.
    Imperial System Abbreviations Metric System Abbreviations
    Abbreviation Measurement Abbreviation Measurement
    -- -- mm millimeter
    in inch cm centimeter
    ft feet m meter
    mi mile km kilometer
    °F Fahrenheit °C Celsius

    Measurement conversions are an important part of the sciences. If you struggle with math, remember, math is a skill to learn, in the same way you learned to read and write. Like learning a language, it takes consistent practice to become fluent. The internet contains a wealth of information -- good, bad, and ugly. You will likely find many conversion tools with a simple Google search; however, the process behind conversions is helpful to learn, particularly if you plan to enter a STEM-based field. Help on conversions is available here.

    Occasionally you many encounter measurements reported in scientific notation. Scientific notation will contain exponents and is useful for measurements that are very small or extremely large (Table 1.2).

    Table 1.2: Scientific notation equivalents for numbers written in decimal notation.
    Decimal notation Scientific notation
    2.00 2 x 100
    300 3 x 102
    4,321.768 4.321768 x 103
    -53,000 -5.3 x 104
    6,720,000,000 6.72 x 109
    0.2 2 x 10-1
    987 9.87 x 102
    0.00000000751 7.51 x 10-9

    When recording measurements, scientists will sometimes indicate scientific error. Errors are differences between observed values and what is true in nature. For measurements, scientists commonly consider both accuracy (how close a measurement is to the true or accepted value) and precision (how close measurements of the same item are to each other). Precision is always independent of accuracy (Figure 1.11). The best quality scientific observations are both accurate and precise.

    Figure 1.11
Precision vs. accuracy using a dart board as an example.
    Figure 1.11: It is possible to be very precise but not very accurate, and it is also possible to be accurate without being precise. In this example, the closer the darts land to the bulls-eye, the more accurate they are.

    What Is Rounding?

    Rounding makes a number simpler but ensures it remains close to the original value. The rounded result is less accurate, but easier to use. This is why you should never round until you are ready to calculate the final answer. Your instructor will likely let you know to what place they would like you to round. So, how do you round numbers? First, identify which place value your instructor prefers you round to (whole number, tenth, hundredth, etc.); ask for clarification if you are unsure. Second, look to the next smallest place value, the digit to the right of the place value you're rounding to. If the digit in the next smallest place value is less than five, you leave the digit as-is. Any digits after that number (including the next smallest place value you just looked at) become zeros, or drop-off if they're located after the decimal point. This is rounding down. If the next smallest place value is greater than or equal to five (5, 6, 7, 8, or 9), you increase the value of the digit you're rounding to by one. Just like before, any remaining digits before the decimal point become zeros, and any that are after the decimal point are dropped. This is called rounding up.

    For example, if we were to round 1.75 cm to the nearest tenth, the new value would become 1.8 cm. If we were asked to round 1.75 cm to the nearest whole number, the new value would become 2 cm.

    1. Identify something that a geologist could measure.
    2. How could a geologist make this measurement?
    3. Why would measuring this be important?
    4. Round 2.9785163 to the nearest hundredth.
    5. Round 96.3452189 years to the nearest whole number.
    6. Round 52.2176493 m to the nearest tenth.
    Table 1.3: Common conversions between the metric and imperial systems.
    Metric System Imperial (English) System
    1 km 0.621371 mi
    1 m 3.28084 ft
    1 cm 0.393701 in
    1. Which is longer, an inch or a centimeter?
    2. Which is longer, a meter or a yard?
    3. Which is longer, a mile or kilometer?
    4. Which is longer, an American football field or a FIFA soccer field?
    5. Convert 10 kilometers to meters.
    6. Convert 10 centimeters to meters.
    1. Convert 10 meters to kilometers.
    1. Convert 10 millimeters to centimeters.
    1. Convert 16 miles to feet.
    1. Convert 16 feet to miles.
    1. Convert 16 feet to inches.
    1. Convert 16 inches to feet.


    • Table 1.1: “Imperial vs. Metric” (CC-BY 4.0; Chloe Branciforte, own work)
    • Table 1.2: “Scientific Notation” (CC-BY 4.0; Chloe Branciforte, own work)
    • Figure 1.11: “Precision vs. Accuracy” (CC-BY 4.0; Emily Haddad, own work)
    • Table 1.3: “Metric and Imperial Comparison” (CC-BY 4.0; Chloe Branciforte, own work)

    This page titled 1.6: Activity 1E - Measurements in Geology is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Chloe Branciforte & Emily Haddad (ASCCC Open Educational Resources Initiative) .

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