Drill Part 1- A single single unit conversion Convert 0.1 (or 10-1) m to ___ cm. Give answer in scientific notation. Part 2 - Draw 3 dart boards • On one, show 6+ darts that have accuracy (on average), but no precision • On another, show 6+ darts that have precision but no accuracy • On the last, show 6+ darts that have accuracy and precision. Target analogy Accuracy (on average) but no precision Target analogy Precision, but no accuracy Target analogy Accuracy & Precision! Extra credit assignment due Wednesday 9/27 • Make a cartoon poster for one safety rule. • If it looks good enough to me, I will laminate it & put it up in the classroom. • It should be: – No dialogue, just pictures with the safety rule as a caption underneath – Big enough to see from across the room – Funny is good, but it needs to be clearly related to the safety rule. Accuracy ≠ Precision!!! • If there is accuracy does not necessarily mean there is precision. • If there is precision does not necessarily mean there is accuracy. Making precision quantitative • Scientists speak in numbers a lot. • 1 = 1.000 000 000? – Not for scientists! • Which number is more precise? • So what? Which would you prefer? Copy & circle column A or B. A B Salary = $1,000/wk Salary = $1000.00/wk Chemistry grade: A Chemistry grade: 96 A few grams of 3.000 grams chemotherapy drug chemotherapy drug $2 Bag of chips $2.50 Bag of chips mass = 500 g mass = 500.1 g Making precision quantitative • When making a measurement, the data should only include meaningful numbers, based on how precise the machine is. • Pour exactly 101 L several times into a graduated cylinder and read volume: – 100.1L, 101.2 L, 103.9 L,102.0 L • Which numbers change? Which stay the same? • Machine is precise only to tens place. Significant Digits (Sig. Dig.) • AKA Significant Figures (Sig. Fig.) • Sig Fig = # of meaningful numbers plus 1st number that has uncertainty: • GC from last slide: – 100.1L, 101.2 L, 103.9 L,102.0 L • 1st number of uncertainty is in singles’ place. • So, when measuring a volume around 100 L in this GC, write down 3 # or 3 Sig. Fig. – 100 L, 101 L, 104 L,102 L Class examples • 4 meausurements: When you are reading other people’s numbers: • All non-zero numbers are significant • All trailing zeroes are significant ONLY IF there is a decimal point • All zeroes between no-zeroes are significant • Place-holder zeroes are not significant.