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SI units and sig figs

SI units and sig figs. SI (systeme internationale). Precision: to describe how well a group of measurements made of the same object or event under the same conditions actually do agree with one another. These points are precise with one another but not accurate.

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SI units and sig figs

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  1. SI units and sig figs

  2. SI (systeme internationale)

  3. Precision: to describe how well a group of measurements made of the same object or event under the same conditions actually do agree with one another. • These points are precise with one another but not accurate.

  4. Accuracy: represents the closeness of a measurement to the true value. • Ex: the bullseye would be the true value, so these points are accurate.

  5. Percent Error • percent error = (exp value - accepted value) x 100%. accepted value • percent difference = | (value1 - value2) | x 100%. average

  6. Using sig figs: The Rules! • Digits from 1-9 are always significant. • Zeros between two other significant digits are always significant • One or more additional zeros to the right of both the decimal place and another significant digit are significant. • Zeros used solely for spacing the decimal point (placeholders) are not significant.

  7. Multiplying and Dividing • RULE: your answer may only show as many sig figs as the multiplied or divided measurement showing the least number of significant digits. • Example: 22.37 cm x 3.10 cm = 69.3 only 3 sig figs allowed.

  8. Adding and Subtracting: • RULE: your answer can only show as many decimal places as the measurement having the fewest number of decimal places. • Example: 3.76 g + 14.83 g + 2.1 g = 20.7 g

  9. Scientific Notation • Scientists have developed a shorter method to express very large or very small numbers.

  10. To write a large number in scientific notation:ex: 36 000 • First put the decimal after the first digit and drop the zeroes. Ex: 3.6 • Next, count the number of places from the decimal to the end of the number. Ex: 4 • Finally, put it together. Ex: 3.6 x 104

  11. To write a small number in s.n.ex: 0.00064 • First move the decimal after the first real number and drop the zeroes. Ex: 6.4 • Next, count the number of places moved from the original decimal spot to the new decimal spot. Ex: 4 • Numbers less than 1 will have a negative exponent. Ex: -4 • Finally, put it together. Ex: 6.4 x 10-4

  12. Uncertainty and sig figs • Sig figs defined as the number of digits known with certainty plus one that is uncertain. • It is certain that the graduated cylinder is filled to 32, but the last digit is an estimation, so is uncertain.

  13. Review • Page 37 # 3,5,8,9 and 11

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