3 SI Units Le Système Internationale d’Unités (SI) Based mostly on the French metric systemSI Units can be base units or derived units
4 Base UnitsA defined unit that is based on an object or event in the physical world.Independent of other units-Time – the SI base unit is the second (s)-Length – the SI base unit is the meter (m)-Mass – the SI base unit is the kilogram (kg)
5 Derived Units A unit that is defined by a combination of base units Dependent on other unitsVolume – can be measure in cm3, dm3, or Liters (L)Density – measured in g/mL, or g/cm3
6 SI Unit PrefixesPrefixes are sometimes added to make lengths more appropriate for measuring
7 Practice How many millimeters are in one meter? How many meters are in one megameter?How many millimeters are in one megameter?How many meters are in one centimeter?How many kilometers are in one meter?How many kilometers are in one centimeter?
8 Density Density is the ratio of mass to volume of an object. The density of a specific substance does not changeA less dense substance will float on a more dense substance.
9 Density Density is calculated using the equation Density (ρ) = mass/volume
10 Practice DensityYou have a rock with a volume of 15cm3 and a mass of 45 g. What is its density?A rectangular block of copper metal weighs g. The dimensions of the block are 8.4 cm by 5.5 cm by 4.6 cm. From this data, what is the density of copper?28.5 g of iron shot is added to a graduated cylinder containing mL of water. The water level rises to the mL mark, From this information, calculate the density of iron.If g of a liquid occupy a space of 35.0 ml, what is the density of the liquid in g/cm3?How many cm3 would a g sample of copper occupy if it has a density of 8.92 g/cm3?What is the mass of the alcohol that exactly fills a mL container? The density of alcohol is g/mL.Find the mass of mL of benzene. The density of benzene is g/mL.
11 Scientific Notation and Dimensional Analysis Section 2.2Scientific Notation and Dimensional Analysis
12 Scientific NotationExpresses numbers as a multiple of two factors: a number between 1 and 10 (the coefficient); and ten raised to a power602,000,000,000,000,000,000,000Easier to write as 6.02x1023Used to make very “bulky” numbers easier to writekg is easier written as x10-27
13 Practice Convert these numbers into scientific notation 700m ) 4,500,000m ) kgkgConvert these numbers into decimal form1.56x ) 6.7x ) X10-24) 9.64X10-11
14 Dimensional AnalysisUsed to convert from one unit to an equivalent value of another unitFor example: If I have 2.5 dozen eggs, how many eggs do I have?We need a conversion factor to convert from dozens of eggs to single eggs.1 dozen = 12 units or 12 units = 1 dozen.Conversion factors set up equivalent values of different units. They can also be written like so:or
15 When you convert from one unit to another Determine what you are given to start withDetermine a conversion factor from our starting units to another unitDetermine how the conversion factor should be set up (what goes on top, what goes on bottom)Carry out the operationIf the units we have after the conversion are not our ending units, repeat steps 2-5 until we arrive at our intended units
16 PracticeOn page 34 and 35, do numbers, for some light practice.
17 How reliable are measurements? Section 2.3How reliable are measurements?
18 Accuracy and Precision Accuracy is how close a measurement is to its standard valuePrecision is how close a series of measurements are to each otherOne can be accurate, but not precise; precise but not accurate; both; or neitherThink of a dartboard
20 Percent ErrorScientists must often determine the precision and accuracy of their experiments.Imprecise or inaccurate data can mean the difference between a success and a failureScientists use a calculation called percent error to evaluate the accuracy of their dataPercent error is the ratio of an error (the difference between their actual results and their expected results) and the expected value
21 Percent ErrorPercent error is calculated through the following equation:
23 Significant FiguresSignificant figures are a way for scientists to indicate the precision of their measurements3.52 is a more precise measurement than 3.5Sig figs include all known digits plus one estimated one
24 If we look at this graduated cylinder measurement, we know for a fact that this is measurement is between 30.3mL and 30.4mL, so to indicate this we estimate where between 30.3mL and 30.4mL to show the precision of our answer. We might estimate that this value is 30.32mL. The last two is our ESTIMATED digit, indicating that we are certain of everything before that
25 The Atlantic-Pacific Rule for Sig Figs The easy way to remember sig fig rules is to remember the Atlantic-Pacific rule Atlantic rule – if the decimal is absent, go to the Atlantic side of the number (the right side) and move left until the first non-zero digit. That digit and all digits to its left are significant 7600 has 2 s.f has 5 s.f. Pacific rule – if the decimal is present, go to the Pacific side of the number (the left side) and move right until you reach the first non-zero digit. That digit and all digits to its right are significant has 2 s.f. 1.2 has 2 s.f.
27 Adding and Subtracting with Sig Figs When adding or subtracting with sig figs, the solution should carry the same number of decimal points to the right of the decimal as the value with the fewest number of decimal places
28 Multiplying and Dividing with Sig Figs When multiplying and dividing with sig figs, the solution should have the same number of sig figs as the value with the least number of sig figs.
29 Sig Figs and Scientific Notation All digits of the coefficient of a number written in scientific notation are always significant.6.02x1023 has 3 sig figs1.0x101 has 2 sig figs
30 PracticeDetermine the number of sig figs in each of the following numbers1200012000.1.2830
31 Practice Determine the answer with the correct number of sig figs 1563/412.565.3*