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Significant Figures Physical Science

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**What is a significant figure?**

There are 2 kinds of numbers: Exact: the amount of money in your account. Known with certainty.

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**What is a significant figure?**

Approximate: weight, height—anything MEASURED. No measurement is perfect.

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**When to use Significant figures**

When a measurement is recorded only those digits that are dependable are written down.

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**When to use Significant figures**

If you measured the width of a paper with your ruler you might record 21.7cm. To a mathematician 21.70, or is the same.

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**But, to a scientist 21.7cm and 21.70cm is NOT the same**

21.700cm to a scientist means the measurement is accurate to within one thousandth of a cm.

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**But, to a scientist 21.7cm and 21.70cm is NOT the same**

If you used an ordinary ruler, the smallest marking is the mm, so your measurement has to be recorded as 21.7cm.

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**How do I know how many Sig Figs?**

Rule: All digits are significant starting with the first non-zero digit on the left.

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**How do I know how many Sig Figs?**

Exception to rule: In whole numbers that end in zero, the zeros at the end are not significant.

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How many sig figs? 7 40 0.5 7 x 105 7,000,000 1

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**How do I know how many Sig Figs?**

2nd Exception to rule: If zeros are sandwiched between non-zero digits, the zeros become significant.

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**How do I know how many Sig Figs?**

3rd Exception to rule: If zeros are at the end of a number that has a decimal, the zeros are significant.

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**How do I know how many Sig Figs?**

3rd Exception to rule: These zeros are showing how accurate the measurement or calculation are.

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How many sig figs here? 1.2 2100 56.76 4.00 0.0792 7,083,000,000 2 4 3

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How many sig figs here? 3401 2100 2100.0 5.00 8,000,050,000 4 2 5 3 6

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**What about calculations with sig figs?**

Rule: When adding or subtracting measured numbers, the answer can have no more places after the decimal than the LEAST of the measured numbers.

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**Add/Subtract examples**

2.45cm + 1.2cm = 3.65cm, Round off to = 3.7cm 7.432cm + 2cm = round to 9cm

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**Multiplication and Division**

Rule: When multiplying or dividing, the result can have no more significant figures than the least reliable measurement.

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**A couple of examples 75.8cm x 9.6cm = ?**

56.78 cm x 2.45cm = cm2 Round to 139cm2 75.8cm x 9.6cm = ?

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**Have Fun Measuring and Happy Calculating!**

The End Have Fun Measuring and Happy Calculating!

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Drill – 9/14/09 How many significant figures: 1.1001.0 2.0.00040 3.4.50 4.1200 Now complete the back of the measurement worksheet from last week (the graduated.

Drill – 9/14/09 How many significant figures: 1.1001.0 2.0.00040 3.4.50 4.1200 Now complete the back of the measurement worksheet from last week (the graduated.

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