Measurement and Accuracy in Science - NOS Quiz

1. September 8th, 2015 • NOS Quiz In 1930, Scotch tape was developed by Richard G. Drew at 3M, St. Paul Minn. Originally, 3M only made sandpaper, and during testing Drew observed at a local auto body shop that auto painters had difficulty making clean dividing lines on two-color paint jobs. After two years of effort in the company's labs, he invented masking tape (1925), a tan paper tape with a light, pressure sensitive adhesive backing. Five years later, he invented Scotch Brand Cellulose Tape, the first waterproof, see-through, pressure-sensitive tape. Once marketed, the public found the tape had a wide range popular applications in mending, sealing and joining. These financial successes stimulated the company to increase product research and development.

2. Objectives • Take Nature of Science Quiz • Accuracy, Precision, & Measurement

3. September 8th, 2015 Assessment Expectations! • Remain quiet during and after your assessment. • Remain seated. Turn your assessment over when finished. I will pick them up at the end of class. • Remain busy. Find something else to work on. Homework • Work on Book readings for Friday.

4. Point of this Lecture 1. Define accuracy & precision and distinguish between the two. 2. Report measurements accurately

5. How close something is to the true/actual/correct answer. Accuracy

6. How close your numbers are to each other. Precision

7. How repeatable are your results. (Can you do it again and get the same answer?) Precision

8. Precision depends on the instrument and the technique used to make the measurement. Generally, the device with the finest division on its scale produces the most precise measurement. Precision

10. Student Practice Section Check Ronald, Kevin, and Paul perform an experiment to determine the value of acceleration due to gravity on the Earth (980 cm/s2). The following results were obtained: Ronald - 961 ± 12 cm/s2, Kevin - 953 ± 8 cm/s2, and Paul - 942 ± 4 cm/s2. Justify who gets the most accurate and precise value.

11. Answer Ronald’s answer is closest to 980 cm/s2 and hence his result is the most accurate. Paul’s measurement is the most precise within 4 cm/s2.

12. 25.0 g 25.0 ml 24.0 g 25.0 ml 100.0 g 100.0 ml 99.0 g 100.0 ml D = D = D = D = = 1.00 g/ml = 0.99 g/ml = 1.00 g/ml = 0.96 g/ml Big Amount or Small Amount Effects of Our Errors with a Small Test Sample 4 % Error Effects of Our Errors with a Large Test Sample 1 % Error

13. Would you rather have a test 10 points or 100 points? If you miss one question on a 10 point test, you have a 90%, but if you miss one point on a 100 point test, you have a 99%

14. When Measuring Use Large Test Samples! The Magnitude of Error is Lowered!

15. Example • What is a “normal” size for a human? • People come in many heights. • Only by averaging the heights of many various people would you be able to determine a normal size. • The amount of people you measure matters, as well. • Yao Ming’s height would skew a small sample, but in a large enough sample, his height would barely change the results. • These individuals that are far off from the norm do matter in the whole population, of course. • The more very tall people (or very short people) there are in a population, the definition of normal height does indeed change.

16. Closing • Book readings are due Friday. Assignment • Read Section 1.2 (pp. 11-14) (Measurement and Accuracy & Precision)