Create placemat and answer the question: Drill Create placemat and answer the question: How many mm are in 3.45dm? Take out Metric Mania HW Take out Book Form

Check for Understanding Complete half sheet and put it in the bin You can use your note sheet! 

Agenda Drill Check for Understanding Create book Accuracy Vs. Precision Sig Fig Rules Bag of Lies HW  Exit Slip

Objectives Evaluate if lab data is precise, accurate, neither, or both Determine the 4 rules of significant figures (sig figs) with your group Apply the 4 rules of sig figs accurately Comprehend the importance of using sig figs for future application of use

Warm-Up I am weighing a rock that I just found on two different scales. When I weigh the rock on a scale found at Dulaney, I find that the rock is 82g. When I weigh the rock on an expensive NASA laser scale, the rock weighs 82.103917g. Does it matter how I record this data? Why or why not?

Accuracy vs. Precision

1 What does the bulls-eye below show? Accuracy Precision Both Neither

2 What does the bulls-eye below show? Accuracy Precision Both Neither

3 What does the bulls-eye below show? Accuracy Precision Both Neither

4 What does the bulls-eye below show? Accuracy Precision Both Neither

Accuracy Definition The closeness of a measurement to its actual value

Reproducibility Repeatability Precision Definition The degree to which measurements show the same or similar results Reproducibility Repeatability

5 Which team was most precise for the two trials? g/cm3 Team 1 Team 2 Team 3 Team 4 Team 5 Team 6 Trial 1 2.75 2.80 2.70 2.71 2.68 Trial 2 2.76 2.73 2.69 2.65 TEAM 6 = SAME DATA IN BOTH TRIALS The density of aluminum is known to be 2.70 g/cm3

6 Which team was most accurate for the two trials? g/cm3 Team 1 Team 2 Team 3 Team 4 Team 5 Team 6 Trial 1 2.75 2.80 2.70 2.71 2.68 Trial 2 2.76 2.73 2.69 2.65 TEAM 4 = AVG 2.70 The density of aluminum is known to be 2.70 g/cm3

How Can We Increase Precision in the Lab? Be honest when reporting a measurement, so that it does not appear to be more accurate than the equipment used to make the measurement allows. We can achieve this by controlling the number of digits, or significant figures, used to report the measurement.

Significant Figure Definition Shorthand way to express how certain one is about one’s data and calculations coming from the data

Rules for Significant Figures

How many digits are significant? # of Sig Figs 459 2.1 .87992 3 2 5

Rule #1 All digits 1-9 are significant

Examples: Number Number of Sig Figs 459 3 2.1 2 .87992 5

How many digits are significant # of Sig Figs 104 1.0402 10.508 10001 3 5

Rule #2 Zeros in between 1-9 digits are significant

Examples Number Number of Sig Figs 104 3 1.0402 5 10.508 10001

How many digits are significant? # of Sig Figs 1.800 8.060 100 100. 100.0 4 1 3

Rule #3 Trailing zeros are significant when there is a decimal point

Examples Numbers Number of Sig Figs 1.800 4 8.060 100 1 100. 3 100.0

How many digits are significant? # of Sig Figs 0.0090 0.0008700 0.470 2 4 3

Rule #4 Place holding zeros are NOT significant

Examples Number How many Sig Figs 0.0090 2 0.0008700 4 0.470 3

Rule #4 Continued Scientific Notation 2.40 x 104 - 3 sig figs The significant digits are the ones before the “x” sign

Bag of Lies There are 20 strips of paper in a bag Goal Determine which strips tell the truth with the correct amount of sig figs and which ones are lies If you are done early, you will be provided with additional questions to answer in your group. There can be more than one rule for the reasoning

Bag of Lies Example Truth or Lie? Why? If lie, how many sig figs?

Challenge: Write your own number Working in pairs with your group, you will be given specific criteria to write a number with an allotted amount of sig figs. You will write the number and then will share with the other group. Groups of 3 will switch from single person to double

Example of Challenge Write a number that is greater than 100 that has 2 significant figures. Examples include: 120 790 580

Challenge questions Give a number between -1 and 1 that has 5 sig figs. Give a number greater than 1,000 that has 2 sig figs. Give a number that is 4 digits but only has 3 sig figs. Give a number less than 1 that has 3 digits, but only 1 sig fig. Give a number that is between 5 and 9 that has 4 sig figs.

HW Watch the sig fig math and measurement video Next Class: Metric Olympics and Measurement

Exit Slip Please complete exit slip What I am collecting Exit Slip Place in the bins! 

Looking Forward Monday Tuesday Wednesday Thursday Friday 29 Measuring in the lab 2 3 Density 4 5 Percent Error 6 9 Review 10 11 Unit 1 Test 12 13