Measurement

Measurement A quantity that has both a number and a unit Which is a measurement? 12 cm 134.54 0.0034

The Metric System Standard units of measurement (SI) Temperature conversion: Quantity Unit Symbol Length meter m Mass kilogram kg Temperature Kelvin K Time second s Amount of substance mole mol Converting temp; think about the alphabet --C to K goes up in the alphabet, so add --K to C goes down in the alphabet so subtract °C + 273 = Kelvin

Metric Prefixes Prefix Meaning Factor Kilo (k) 103 Centi (c) 10−2 1000 times larger than the unit 103 Centi (c) 100 times smaller than the unit 10−2 Milli (m) 1000 times smaller than the unit 10−3 Micro (μ) 1 million times smaller than the unit 10−6 Nano (n) 1 billion times smaller than the unit 10−9

Scientific Notation Used to write really big and small numbers 6.02 ×1023 The coefficient is equal to or greater than 1 and less than 10 The exponent is a positive or negative integer Circle and label coefficient

Writing Scientific Notation For large numbers— move the decimal to the left until one digit remains in front Count the number of times the decimal moves The exponent is positive Example: 3,000  3 ×103 405,000  4.05 ×105 Underline large numbers, left, positive

For small numbers— move the decimal to the right until one digit is in front Count the number of times the decimal moves The exponent is negative Example: 0.00034  3.4 ×10−4 0.0000005070  4.05 ×10−6 Underline small numbers, right, negative

Accuracy How close a measurement comes to the actual value of whatever is measured The more # of significant digits, the more accurate the value

Precision How close a series of measurements are to one another or “repeatability” You must compare two or more measurements to each other

Accuracy vs Precision

Example: Jack has a height of 70 inches. Which sets of measurements are Accurate and precise Precise but not accurate Neither precise nor accurate 69.5 in., 70.5 in., 70.1 in. 45.3 in., 62.1 in., 84.3 in 78.3 in., 78.0 in., 78.1 in

Percent Error To find out how close you are to an accepted or actual value Percent error =  exp val – act val  x 100% act val error Point out the absolute value sign, we don’t care if we measured high or low

Example: Your data reads 99. 1g but the accepted value is 101 Example: Your data reads 99.1g but the accepted value is 101.0g, what is your percent error? Percent error = 99.1g − 101.0g × 100 101.0g %error = 1.88% Point out the absolute value sign, we don’t care if we measured high or low