Presentation on theme: "1 Chapter 2 Scientific measurement 2 Types of measurement l Quantitative- use numbers to describe l Qualitative- use description without numbers l 4."— Presentation transcript:
1 Chapter 2 Scientific measurement
2 Types of measurement l Quantitative- use numbers to describe l Qualitative- use description without numbers l 4 feet l extra large l Hot l 100ºF
3 Scientists prefer l Quantitative- easy to check l Easy to agree upon, no personal bias l The measuring instrument limits how good the measurement is
4 How good are the measurements? l Scientists use two words to describe how good the measurements are l Accuracy- how close the measurement is to the actual value l Precision- how well can the measurement be repeated
5 Differences l Accuracy can be true of an individual measurement or the average of several l Precision requires several measurements before anything can be said about it l examples
6 Lets use a golf anaolgy
7 Accurate?No Precise?Yes
8 Accurate?Yes Precise?Yes
9 Precise?No Accurate?Maybe?
10 Accurate?Yes Precise?We cant say!
11 In terms of measurement l Three students measure the room to be 10.2 m, 10.3 m and 10.4 m across. l Were they precise? l Were they accurate?
12 Significant figures (sig figs) l How many numbers mean anything l When we measure something, we can (and do) always estimate between the smallest marks. 21345
13 Significant figures (sig figs) l The better marks the better we can estimate. l Scientist always understand that the last number measured is actually an estimate 21345
14 Sig Figs l What is the smallest mark on the ruler that measures 142.15 cm? l 142 cm? l 140 cm? l Does the zero count or not? l A set of rules is needed to decide which zeroes count. l All other numbers do count
15 Which zeros count? l Those at the end of a number before the decimal point dont count l 12400 l If the number is smaller than one, zeroes before the first number dont count l 0.045
16 Which zeros count? l Zeros between other sig figs do. l 1002 l zeroes at the end of a number after the decimal point do count l 45.8300 l If they are holding places, they dont. l If they are measured (or estimated) they do
17 Sig Figs l Only measurements have sig figs. l Counted numbers are exact l A dozen is exactly 12 l A a piece of paper is measured 11 inches tall. l Being able to locate, and count significant figures is an important skill.
18 Sig figs. l How many sig figs in the following measurements? l 458 g l 4085 g l 4850 g l 0.0485 g l 0.004085 g l 40.004085 g
19 Sig Figs. l 405.0 g l 4050 g l 0.450 g l 4050.05 g l 0.0500060 g l Next we learn the rules for calculations
20 More Sig Figs
21 Problems l 50 is only 1 significant figure l if it really has two, how can I write it? l A zero at the end only counts after the decimal place l Scientific notation l 5.0 x 10 1 l now the zero counts.
22 Adding and subtracting with sig figs l The last sig fig in a measurement is an estimate. l Your answer when you add or subtract can not be better than your worst estimate. l have to round it to the least place of the measurement in the problem
23 For example 27.936.4+ l First line up the decimal places 27.93 6.4+ Then do the adding 34.33 Find the estimated numbers in the problem 27.93 6.4 This answer must be rounded to the tenths place
24 Rounding rules l look at the number behind the one youre rounding. l If it is 0 to 4 dont change it l If it is 5 to 9 make it one bigger l round 45.462 to four sig figs l to three sig figs l to two sig figs l to one sig fig
25 Multiplication and Division l Rule is simpler l Same number of sig figs in the answer as the least in the question l 3.6 x 653 l 2350.8 l 3.6 has 2 s.f. 653 has 3 s.f. l answer can only have 2 s.f. l 2400
26 Multiplication and Division l Same rules for division
27 The Metric System An easy way to measure
28 Measuring l The numbers are only half of a measurement l It is 10 long l 10 what. l Numbers without units are meaningless. l How many feet in a yard l A mile l A rod
29 The Metric System l Easier to use because it is a decimal system l Every conversion is by some power of 10. l A metric unit has two parts l A prefix and a base unit. l prefix tells you how many times to divide or multiply by 10.
30 Base Units l Length - meter more than a yard - m l Mass - grams - a bout a raisin - g l Time - second - s l Temperature - Kelvin or ºCelsius K or C l Energy - Joules- J l Volume - Liter - half f a two liter bottle- L l Amount of substance - mole - mol
31 Prefixes l kilo k 1000 times l deci d 1/10 l centi c 1/100 l milli m 1/1000 l kilometer - about 0.6 miles l centimeter - less than half an inch l millimeter - the width of a paper clip wire
32 Volume l calculated by multiplying L x W x H l Liter the volume of a cube 1 dm (10 cm) on a side l so 1 L = 10 cm x 10 cm x 10 cm l 1 L = 1000 cm 3 l 1/1000 L = 1 cm 3 l 1 mL = 1 cm 3
33 Volume l 1 L about 1/4 of a gallon - a quart l 1 mL is about 20 drops of water or 1 sugar cube
34 Mass l weight is a force, is the amount of matter. l 1gram is defined as the mass of 1 cm 3 of water at 4 ºC. l 1000 g = 1000 cm 3 of water l 1 kg = 1 L of water
35 Mass l 1 kg = 2.5 lbs l 1 g = 1 paper clip l 1 mg = 10 grains of salt or 2 drops of water.
36 Converting khDdcm l how far you have to move on this chart, tells you how far, and which direction to move the decimal place. l The box is the base unit, meters, Liters, grams, etc.
37 Conversions l Change 5.6 m to millimeters khDdcm l starts at the base unit and move three to the right. l move the decimal point three to the right 5600
38 Conversions l convert 25 mg to grams l convert 0.45 km to mm l convert 35 mL to liters l It works because the math works, we are dividing or multiplying by 10 the correct number of times khDdcm
39 Conversions l Change 5.6 km to millimeters khDdcm
40 Density l how heavy something is for its size l the ratio of mass to volume for a substance l D = M / V l Independent of how much of it you have l gold - high density l air low density.
41 Calculating l The formula tells you how l units will be g/mL or g/cm 3 l A piece of wood has a mass of 11.2 g and a volume of 23 mL what is the density? l A piece of wood has a density of 0.93 g/mL and a volume of 23 mL what is the mass?
42 Calculating l A piece of wood has a density of 0.93 g/mL and a mass of 23 g what is the volume? l The units must always work out. l Algebra 1 l Get the thing you want by itself, on the top. l What ever you do to onside, do to the other
43 Floating l Lower density floats on higher density. l Ice is less dense than water. l Most wood is less dense than water l Helium is less dense than air. l A ship is less dense than water