I II III Accuracy, Precision, Percent Error 101 MEASUREMENT

Learning Objectives  The Learners Will (TLW) collect data and make measurements with accuracy and precision, and will be able to calculate percent error  TEKS 2F

Agenda  Part 1 – Units of Measurements  A. Qualitative Measurements vs. Quantitative Measurements  B. Number versus Quantity  C. Experimental Value  D. Review SI Units  E. Derived Units  Part 2 – Using Measurement  A. Accuracy vs. Precision  B. Precision of Measurement  C. Percent Error  Mini-Lab

I. Units of Measurement

 Everyone makes and uses measurements  Examples from the studio audience  Measurements are fundamental to experimental sciences as well  Important to be able to make measurements and to decide whether it is correct

A. Qualitative vs. Quantitative Measurement  Qualitative Measurement – a measurement that gives descriptive, nonnumeric results  Examples –  Touching a person’s forehead to check for fever  Determining the winner of the Kentucky Derby by watching the horses cross finish line  Others from learners  Can vary by experimenter

A. Qualitative vs. Quantitative Measurement  Quantitative Measurement – a measurement that gives definite, usually numeric results that also includes units  Examples –  Using a thermometer to measure a person’s temperature at 99.2 °F (37.2 °C)  Using a photogate to capture time horses cross finish line at Kentucky Derby  Others from learners

B. Number vs. Quantity  Quantity = number + unit UNITS MATTER!!

C. Experimental Value  A quantitative value measured during an experiment  Examples –  Mass of rubber stopper  Volume displaced when stopper was dropped into graduated cylinder of water  Temperature change of a reaction

D. SI Units QuantityBase UnitAbbrev. Length Mass Time Temp meter kilogram second Celsius or Kelvin m kg s °C or °K Amount molemol Symbol l m t T n

D. SI Units mega-M10 6 deci-d10 -1 centi-c10 -2 milli-m10 -3 PrefixSymbolFactor micro-  nano-n10 -9 pico-p kilo-k10 3 BASE UNIT

E. Derived Units  Combination of base units.  Volume (m 3 or cm 3 )  height  width  length D = MVMV 1 cm 3 = 1 mL 1 dm 3 = 1 L  Density (kg/m 3 or g/cm 3 )  mass per volume

I II III II. Using Measurements

Trasketball Need 5 volunteers – 5 shots eact

A. Accuracy vs. Precision  Accuracy - how close a measurement is to the accepted value (published, target)  Precision - how close a series of measurements are to each other ACCURATE = CORRECT PRECISE = CONSISTENT

A. Accuracy vs. Precision  PRECISE – a golfer hits 20 balls from the same spot out of the sand trap onto the fringe of the green. Each shot is within 5 inches of one another. Wow – that’s CONSISTENT  ACCURATE – the golfer’s 20 shots aren’t very accurate, because they need to be much closer to the hole so she can score easily – that would be CORRECT

Audience Participation Let’s Play The Accuracy or Precision Game

Calculating Precision  Determine the average of all data values  Determine the spread between highest and lowest values (highest – lowest = spread)  Divide the spread by 2  This is the approximate range + from the average  Precision of measurement is shown as average + range

Calculating Precision - Example Distance 1Distance 2Distance 3Distance 4Distance 5Distance m2.0 m1.5 m1.7 m1.6 m1.3 m Average distance = 9.6 m total / 6 readings = 1.6 m Highest value (2.0 m) – Lowest value (1.3 m) = 0.7 m 0.7 m is the spread Divide by 2 = 0.35 m ( range from average ) Precision of measurement is 1.6 m m

Calculating Precision - Practice Distance 1Distance 2Distance 3Distance 4Distance 5Distance m2.0 m2.5 m2.7 m2.6 m2.3 m -- In groups of 2, calculate precision of the following -- Round to 2 decimal places -- Raise your hand when your team is done. Precision of measurement is ____ m + _____ m Temp 1Temp 2Temp 3Temp 4Temp 5Temp °C98.0 °C98.2 °C98.1 °C 98.3 °C Precision of measurement is ____ °C + _____ °C Which set of measurements is more precise? Distance or Temp?

B. Percent Error  Indicates accuracy of a measurement your value accepted value

B. Percent Error  A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL. % error = 2.9 %

B. Percent Error  In groups of 2 calculate the percent error  Round to 2 decimal places  Raise your hand when your team is done 1. Experimental Value = 5.75 g Actual Value = 6.00 g 2. Experimental Value = 107 ml Actual Value = 105 ml 3. Experimental Value = 1.54 g/ml Actual Value = 2.35 g/ml

Let’s Experiment… 1. Measure the wooden block with the formula chart ruler 2. Measure the level in the graduated cylinder 3. Measure the level in the beaker 4. Write your name on the chart at the front of the room and record the above measurements in the columns indicated

Lab Results  Did we all come up with exactly the same numbers?  Why or Why not?  Which are most precise measurements?  Why?  Which are most accurate measurements?  Why?  What’s the precision of the measurements?  Perform the calculations  What is the percent error?  Perform the calculations

Check for Understanding  Accuracy – Correctness of data  Precision – Consistency of results  Precision of Measurement – Determining the spread from average value (tolerance)  Percent Error – Comparison of experimental data to published data

Check for Understanding  How can you ensure accuracy and precision when performing a lab?  What is the percent error when lab data indicates the density of molasses is 1.45 g/ml and Perry’s Handbook for Chemical Engineering shows 1.47 g/ml?

Independent Practice  Accuracy and Precision Worksheet 1 Accuracy and Precision Worksheet 1  Accuracy and Precision Pre-test Accuracy and Precision Pre-test