1. Description and Measurement Ms. Pollock 8th Grade Physical Science 2009 - 2010

2. Measurement 4 Way to describe world using numbers 4 how much, how long, how far 4 more reliable than opinion 4 describes events –Olympics

3. Estimation 4 Rough measurement 4 using something familiar to guess size of new object 4 based on previous experience –chefs –firefighters

4. Estimation 4 Use “about” 4 check for reasonable answers –doorknobs about 1 m from floor –sack of flour about 2 kg –walk about 5 km/h

5. Precision and Accuracy 4 Precision: how close measurements are to each other 4 same every time 4 also number of decimal places possible with particular tool 4 degrees of precision

6. Precision and Accuracy 4 Accuracy: comparison of measurement to real, actual, or accepted value 4 How close you are to the desired value

7. Precision and Accuracy 4 Important to medical procedures –Stereotactic Radiotherapy (SRT) –treatment of brain cancer without damaging healthy cells

8. Rounding a Measurement 4 Some instruments not capable of great precision 4 rounding rules important for estimation –digit to right of digit being rounded is 0, 1, 2, 3, or 4: number remains same –digit to right of digit being rounded is 5, 6, 7, 8, or 9: number increases by one –digits to right of digit being rounded are right of decimal: delete them –digits to left of digit being rounded are left of decimal: change to zeros

9. Rounding a Measurement 4 Length of sidewalk 135.841 m 4 rounded to tenths place –135.8 m –digit to right of tenths place (number 8) was 4 4 rounded to ones place –136 m –digit to right of ones place (number 5) was 8

10. Precision and Number of Digits 4 Rounding necessary when numbers do not divide evenly 4 digits that reflect precision significant –digits other than zero –final zeros after decimal point (6.545 600 g) –zeros between other digits (507.0301 g) –initial zeros NOT significant (0.000 2030 g) –zeros in whole number possibly significant (1650) –numbers counted, rather than measured

11. Applying Math: Rounding 4 The mass of one object is 6.941 g. The mass of a second object is 20.180 g. You need to know these values only to the nearest whole number to solve a problem. What are the rounded values? 4 6.941 g (number to right of ones place = 9) –7 (rounded up) 4 20.180 g (number to right of ones place = 1) –20 (remained same)

12. Following the Rules 4 Rules for determining significant figures in calculations –multiplication and division determined by number with fewer digits 6.14 X 5.6 = 34.384 3 2 2 –addition and subtraction least precise place value 6.14 + 5.6 = 11.74 100s 10s 10s