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Significant Figures Every measurement has a limit on its accuracy based on the properties of the instrument used. we must indicate the precision of the measurement by using the correct number of significant figures Precision – the consistency of a measurement, how repeatable it is

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**Can you name this significant figure?**

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**Check your answer with the person next to you**

Object A, measured with Ruler I should be recorded as ________ but as measured with Ruler II should be recorded as _________ Check your answer with the person next to you

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**Check your answer with the person next to you**

Object B, measured with Ruler I is _______________ Object B, measured with Ruler II is _______________ Check your answer with the person next to you

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**Which ruler is the most precise?**

Which ruler is the least accurate?

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**What happens if an object is directly on the 3 of the ruler**

What happens if an object is directly on the 3 of the ruler? What decimal place to record?

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**Check your answer with the person next to you**

what is its smallest division? _________ How should measurements using Ruler IV be recorded (to how many decimal places)? ________ Check your answer with the person next to you

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**Rules for SigFigs Nonzero digits are ALWAYS significant**

Zeroes are only sometimes significant… All final zeroes after a decimal point are significant Zeroes between two other significant digits are always significant Zeroes used soley as placeholders are NOT significant Zeroes between a decimal point and a nonzero digit are NOT significant.

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Some examples m s m $18,000 $18,000.00 $18,000. cm

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**1. Give the number of sig. fig**

1. Give the number of sig. fig. and the number of decimal places in each of the number below. a) b) c) d) e) 3,000 f) 3,000. g) 3,000.00

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# of sig. fig. # of decimal places a) 72.32 4 2 b) 5 3 c) 0.003 1 d) e) 3,000 assume 1 f) 3,000. g) 3,000.00 6

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**2. These numbers have ambiguous zeroes**

2. These numbers have ambiguous zeroes. Remove the ambiguity by expressing them in scientific notation. a) in 2 sig. fig. b) in 3 sig. fig. c) in 4 sig. fig. d) 2100 in 3 sig. fig. e) 790,000 in 4 sig. fig. f) 3800 x 10-7 in 3 sig. fig.

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Answers a) in 2 sig. fig. 4.2 x104 b) in 3 sig. fig. 4.20 x 104 c) in 4 sig. fig. 4.200 x 104 d) 2100 in 3 sig. fig. 2.10 x 103 e) 790,000 in 4 sig. fig. 7.900 x 105 f) 3800 x 10-7 in 3 sig.fig. 3.80 x 10-4

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When you perform any arithmetic operation, it is important to remember that the result can never be more precise than the least precise measurement.

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**Adding and Subtracting**

To add or subtract measurements, first perform the operation, then round off the result to correspond to the least precise value involved. For example, add these values: m m m = m 3.21m Least precise measurement? ______ Round answer to _______ 30.24m

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Multiply and Divide After performing the calculation, note the factor that has the least number of significant digits. Round the product or quotient to this number of digits. For example, multiply 3.22 cm by 2.1 cm = cm2 corrected to _________ 6.8 cm2

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**36.5 m divided by 3.414 s = 10.691 m/s corrected to ________**

Divide these two measurements and report answer with correct number of significant digits 36.5 m divided by s = m/s corrected to ________ 10.7 m/s

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**Let’s review… Some Practice problems 1) 2804m 2) 2.84km 3)0.029m **

4) m 5) 4.6x105m 6) 4.06x105m 7) 750m 8) 75m 9)75,000 m 10) 75,000. m 11) 75,000.0m 12) 10 cm

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**Answers Some Practice problems 1) 2804m 2) 2.84km 3)0.029m **

4) m 5) 4.6x105m 6) 4.06x105m 7) 750m 8) 75m 9)75,000 m 10) 75,000. m 11) 75,000.0m 12) 10 cm

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**More practice! 1) 6.201 cm + 7.4 cm + 0.68 cm + 12.0 cm = ?**

2) 1.6 km + 1.62 m + 1200 cm = ? 3) g - 7.8 g = ? 4) m - 6.0 m = ? 5) m + kg = ? 6) 131 cm x 2.3 cm = ? 7) m x m = ? 8) 20.2 cm divided by 7.41 s = ? 9) g divided by ml = ?

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