Agenda Accuracy Vs Precision Sig Fig Rules Bag

Agenda Accuracy Vs. Precision Sig Fig Rules Bag of Lies Kahoot Get back unit test HW

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 82. 11 g. When I weigh the rock on an expensive NASA laser scale, the rock weighs 82. 103917 g. Does not? it matter how I record this data? Why or why

Accuracy vs. Precision

1 What does the bulls-eye below show? A. Accuracy B. Precision C. Both D. Neither

2 What does the bulls-eye below show? A. Accuracy B. Precision C. Both D. Neither

3 What does the bulls-eye below show? A. Accuracy B. Precision C. Both D. Neither

4 What does the bulls-eye below show? A. Accuracy B. Precision C. Both D. Neither

Accuracy Definition The closeness of a measurement to its actual value

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? Team Team 1 2 3 4 5 6 Trial 1 2. 75 2. 80 2. 71 2. 68 g/cm 3 Trial 2 2. 76 2. 73 2. 69 2. 65 2. 68 The density of aluminum is known to be 2. 70 g/cm 3

6 Which team was most accurate for the two trials? Team Team 1 2 3 4 5 6 Trial 1 2. 75 2. 80 2. 71 2. 68 g/cm 3 Trial 2 2. 76 2. 73 2. 69 2. 65 2. 68 The density of aluminum is known to be 2. 70 g/cm 3

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? Digit # of Sig Figs 459 3 2. 1 2 . 87992 5

Rule #1 All digits 1 -9 are significant

Examples: Number of Sig Figs 459 3 2. 1 2 . 87992 5

How many digits are significant Digit # of Sig Figs 104 3 1. 0402 5 10. 508 5 10001 5

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

Examples Number of Sig Figs 104 1. 0402 10. 508 10001 3 5 5 5

How many digits are significant? Digit # of Sig Figs 1. 800 4 8. 060 4 100 1 100. 3 100. 0 4

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

Examples Number of Sig Figs 1. 800 8. 060 100. 0 4 4 1 3 4

How many digits are significant? Digit # of Sig Figs 0. 0090 2 0. 0008700 4 0. 470 3

Rule #4 Place holding zeros are NOT significant

Examples Number How many Sig Figs 0. 0090 0. 0008700 0. 470 2 4 3

Rule #4 Continued with Scientific Notation 2. 41 x 104 - 3 sig figs The significant digits are the ones before the “x” sign

Exact Numbers Exact numbers, such as the number of people in a room, have an infinite number of significant figures. Exact numbers are counting up how many of something are present, they are not measurements made with instruments. Therefore, if a number is exact, it DOES NOT affect the accuracy of a calculation or the precision of the expression.

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 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 120 790 580 include:

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 All Watch If video about sig fig math and measurement you don’t know scientific notation Watch scientific notation video and take notes