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SI units and sig figs

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**SI (systeme internationale)**

Physical Quantity Unit Symbol Length Metre m Mass Kilogram kg Time Second s Temperature Kelvin K Amount of substance Mole mol Electric current Ampere A Luminous intensity Candela cd

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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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**Accuracy: represents the closeness of a measurement to the true value.**

Ex: the bullseye would be the true value, so these points are accurate.

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**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.

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EXAMPLES # OF SIG. FIG. COMMENT 453kg 3 All non-zero digits are always significant. 5057L 4 Zeros between 2 sig. fig. are significant. 5.00 Additional zeros to the right of decimal and a sig. fig. are significant. 0.007 1 Placeholders are not sig. fig

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**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: cm x 3.10 cm = 69.3 only 3 sig figs allowed.

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**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 g g = 20.7 g

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Scientific Notation Scientists have developed a shorter method to express very large numbers. Scientific Notation is based on powers of the base number 10.

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123,000,000,000 in s.n. is 1.23 x 1011 The first number 1.23 is called the coefficient. It must be between The second number is called the base . The base number 10 is always written in exponent form. In the number 1.23 x 1011 the number 11 is referred to as the exponent or power of ten.

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**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

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**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

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Significant Numbers All numbers in a measurement that are reasonable and reliable.

Significant Numbers All numbers in a measurement that are reasonable and reliable.

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