Presentation on theme: "SI units and sig figs. SI (systeme internationale) Physical Quantity UnitSymbol LengthMetrem MassKilogramkg TimeSeconds TemperatureKelvinK Amount of substance."— Presentation transcript:
SI units and sig figs
SI (systeme internationale) Physical Quantity UnitSymbol LengthMetrem MassKilogramkg TimeSeconds TemperatureKelvinK Amount of substance Molemol Electric currentAmpereA Luminous intensity Candelacd
Precision: to describe how well a group of measurements made of the same object or event under the same conditions actually do agree with one another. These points are precise with one another but not accurate.
Accuracy: represents the closeness of a measurement to the true value. Ex: the bullseye would be the true value, so these points are accurate.
Percent Error percent error = (exp value - accepted value) x 100%. accepted value percent difference = | (value1 - value2) | x 100%. average
Using sig figs: The Rules! 1.Digits from 1-9 are always significant. 2.Zeros between two other significant digits are always significant 3.One or more additional zeros to the right of both the decimal place and another significant digit are significant. 4.Zeros used solely for spacing the decimal point (placeholders) are not significant.
EXAMPLES# OF SIG. FIG. COMMENT 453kg3All non-zero digits are always significant. 5057L4Zeros between 2 sig. fig. are significant Additional zeros to the right of decimal and a sig. fig. are significant Placeholders are not sig. fig
Multiplying and Dividing RULE: your answer may only show as many sig figs as the multiplied or divided measurement showing the least number of significant digits. Example: cm x 3.10 cm = 69.3 only 3 sig figs allowed.
Adding and Subtracting: RULE: your answer can only show as many decimal places as the measurement having the fewest number of decimal places. Example: 3.76 g g g = 20.7 g
Scientific Notation Scientists have developed a shorter method to express very large or very small numbers.
To write a large number in scientific notation: ex: First put the decimal after the first digit and drop the zeroes. Ex: 3.6 Next, count the number of places from the decimal to the end of the number. Ex: 4 Finally, put it together. Ex: 3.6 x 10 4
To write a small number in s.n. ex: First move the decimal after the first real number and drop the zeroes. Ex: 6.4 Next, count the number of places moved from the original decimal spot to the new decimal spot. Ex: 4 Numbers less than 1 will have a negative exponent. Ex: -4 Finally, put it together. Ex: 6.4 x 10 -4
Uncertainty and sig figs Sig figs defined as the number of digits known with certainty plus one that is uncertain. It is certain that the graduated cylinder is filled to 32, but the last digit is an estimation, so is uncertain.