Presentation on theme: "Observations Qualitative Quantitative (measurements) Two parts needed"— Presentation transcript:
1 Observations Qualitative Quantitative (measurements) Two parts needed Observed directlyColor, texture, magnetic, state of matter, etcQuantitative (measurements)Two parts neededNumber AND unit(Naked numbers are meaningless)
20 Uncertainty in Measurements Measurement is only as good as the “measuring” instrumentMust choose an appropriate deviceTo weigh your cat, should you use a truck weigh station or a baby scale? Why?
21 The number of digits that you can actually “count” for a real measurement depends upon the measuring device.Includes all measured number plus one “uncertain” last digit, which is estimatedCan only estimate one place beyond the lines or marks
22 Significant figures - all digits in a number representing data or results that are known with certainty plus one uncertain digit.
23 Suppose that two people read the bottom ruler and get measurements of 5.36 cm and 5.37 cm. Which one is the correct reading?
24 5.4 cm +/ cm (5.3 – 5.5 cm)5.36 cm +/ cm ( cm)Which has less uncertainty?5.4 (ca 2%) (ca 0.2%)
25 Uncertainty in Measurements Measuring device determines uncertainty and number of significant digits (numbers that have meaning)
26 Accuracy and Precision Accuracy: How close measurements are to actual valuePrecision: How close measurements are to each other