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Ch 5 How to take measurements and make proper calculations

Ch 5 How to take measurements and make proper calculations. We will deal with many types of measurements and calculations throughout the year. The types of values you will encounter are given data, collected data, and calculated data. Knowing what and how to handle these numbers is essential.

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Ch 5 How to take measurements and make proper calculations

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  1. Ch 5 How to take measurements and make proper calculations • We will deal with many types of measurements and calculations throughout the year. The types of values you will encounter are given data, collected data, and calculated data. Knowing what and how to handle these numbers is essential.

  2. Taking Measurements • When taking measurements it is important that you are as accurate and precise as possible. • Accuracy is how close your measurement is to the correct value. • Precision is how closely your measurements are to each other. • Being precise also involves taking your measurements to the maximum number of digits. • Using the right equipment will help in both precision and accuracy.

  3. Use of Significant Figures • The precision of a collected value or calculated value is indicated by the number of significant figures the number contains. • The greater the number of significant figures the greater the precision. • Making calculations with numbers should not change their significance. • Use the rules of significant figures to correctly round off your calculator values.

  4. Exact Numbers • Exact numbers have infinite precision. • Only collected measurements are under the rules of significant figures. • Numbers that are indicating exact amounts are not included. • A dozen people • 45 atoms • Divided among 6 groups

  5. Significant figure rules • Non-zero digits are significant • Zeros between non-zero digits are significant • Zeros at the end of a number are not significant unless the are after the decimal point. • Zeros at the beginning of a number less than 1 are not significant.

  6. How many Significant Figures? • 1.021 • 253 • 500 • 0.00203 • 6.022 • .0004 • 22.34

  7. Using Significant Figures • Rule for multiplication/division • Round the answer to the number indicated by the calculated value with the least number of significant figures • Rule for addition/subtraction • Round the answer to the place of the least significant number by place

  8. Using Significant Figures • Rule #1 Multiplication/Division • The mass of an object is 5.0 grams and its volume is 2.75 mL. Calculate its density. • D = m/V D = 5.0/2.75 = 1.81818181818 • Round this off to 1.8 because of the 5.0 value has 2 sig. figs.

  9. Using Significant Figures • Rule #2 Addition/Subtraction • 212.2 + 26.7 + 402.09 = • 641.0 • Raw is 640.99, round to the least significant place

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