1. Aim: How do scientists make and report their observations? Do Now: 1.Take out a calculator. 2.In your own words, describe how you would measure the length of the smart board.

2. Measuring the smart board… How could the length of the smart board be measured and recorded? What is the difference between these measurements?

3. Precision –v- Accuracy Accuracy – The closeness of a measurement to the true value of what is being measured. Precision – Describes the closeness, or reproducibility of a set of measurements taken under the same circumstances.

4. An Example Suppose I need to weigh some grapes at the grocery store. Is the scale precise or accurate? In terms of precision, the scale is precise if I can reproduce the results on other scales in similar circumstances. In terms of accuracy, the closer the scale is to the actual measurement of the grape’s weight, the more accurate it is. How can I increase the accuracy of the scale? How do scientists show that accuracy? They use significant figures.

5. How can we tell how many “sig. figs.” there are? **The Atlantic – Pacific Rule** When a decimal is Present in a measurement, start on the Pacific (left) side of the number with the first nonzero digit. ALL following digits (including zeroes) are significant. Examples: 2.5 has 2 sig. figs. 0.0321 has 3 sig. figs. 300.1 has 4 sig. figs. 40.035 has 5 sig. figs. 0.000123450 has 6 sig. figs.

6. How can we tell how many “sig. figs” there are? **The Atlantic – Pacific Rule** When a decimal is Absent in a measurement, start on the Atlantic (right) side with the first nonzero digit. ALL numbers to the left of that number are significant. Examples: 23 has 2 sig. figs. 921 has 3 sig. figs. 1045 has 4 sig. figs. BUT…..... 20,00,000 has 1 sig. fig.

7. Some More Practice Problems How many sig. figs. are there in the following numbers? 1.5.9 2.463.1 3.6584.0 4.0.063 5.0.12350

8. What happens when we calculate using sig. figs.? When there is math involved, the number with the LEAST sig. figs. determines how many sig. figs. there are in the answer. That determination must be done at the end of the calculation. Example: 2.5 + 2.57= 5.07. However, 2.5 only has 2 sig figs. Therefore, the answer has to be 5.0 to satisfy the Atlantic- Pacific rule.

9. Some practice problems: Calculate the answers to the following. SHOW SIGNIFICANT FIGURES FOR EACH ANSWER. 1.10.3 + 2.55 2.11 x 2.91 3.55.0 – 3.25 4.6.0001 + 15.987 5.20 x 5.1

10. Homework # How many sig figs are there? 1.3.006 2.500,001 3.2.0 + 3.9 (solve and show sig figs) 4.82.3 – 10.04 (solve and show sig figs) 5.1999 x 2.0 (solve and show sig figs)