Description and Measurement Ms. Pollock 8th Grade Physical Science

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

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

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

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

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

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

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

Rounding a Measurement 4 Length of sidewalk 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

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 ( g) –zeros between other digits ( g) –initial zeros NOT significant ( g) –zeros in whole number possibly significant (1650) –numbers counted, rather than measured

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

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 = –addition and subtraction least precise place value = s 10s 10s