Thinking Scientifically

“Insanity is doing the same thing over and over expecting different results” ~Einstein

The Scientific Method

State the ProblemGather InformationState your HypothesisTest your HypothesisObserve and Collect DataDraw Conclusions

Making ObservationsThere are two types of

observations:1. A qualitative observation does not

involve a number. The sky is blue. Water is a liquid.

2. A quantitative observation (also called a measurement) involves both a number and a unit. Water boils at a temperature of 100.°C. The book has a mass of 2.04 kg.

Steps to Thinking Scientifically

Forming Hypotheses. ◦A hypothesis in a possible explanation for an

observation.Performing experiments.

◦An experiment is carried out to test a hypothesis. This involves gathering new information that enables

a scientist to decide whether the hypothesis is valid – that is, whether it is supported by the new information learned from the experiment.

Experiments always produce new observations, and this brings the process back to the beginning again.

Scientific ModelsTheory – an attempted interpretation, or

a possible explanation of why nature behaves in a particular way.

Law – A tried and tested explanation of nature that has been observed to be true, or a summary of what always happens.

The point of scientific experimentation is to test theories and shape them into laws that are truths about nature.

Units of MeasureThe SI System

◦ Scientists measure using a universal system called the International System.

SI UnitsPhysical Quantity Name AbbrMass kilogram kgLength meter mTime second sTemperature kelvin KElectric Current ampere AAmount of Substance mole molLuminous Intensity candela cd

Scientific NotationScientists often consider

numbers that are inconvenient to write out or type into a calculator.◦Think of the grains of sand on a

beach…◦Think of how many meters to the

moon…We use scientific notation

because we need it.

Practice: Scientific NotationExpress the following numbers in

scientific notation:◦238,000

2.38 x 105

◦1,500,000 1.5 x 106

◦357 3.57 x 102

Practice: Scientific NotationExpress the following numbers in

scientific notation:◦0.00043

4.3 x 10-4

◦0.089 8.9 x 10-2

◦0.0055 4.3 x 10-3

Practice

Prefixes Used in the SI System

Significant Figures

Resistance is Futile!

; )

What is a significant figure?AKA “sigfigs”A significant figure is a number

that matters in a calculation.All scientific calculations must

consider significance.In science, answers are not

considered entirely correct unless the correct number of significant figures are used.

How much is regular gas?

Why is this so important?Significant figures represent the numbers

in a final calculation that are known to be true without error.◦Some numbers come from measurements.

ALL measurements made are inaccurate and contain some degree of error.

Significant figures account for this error.Basically your answer cannot be more

precise or more accurate than the tool used to make the measurement.

The Rules of SignificanceAll nonzero integers are significant.Leading Zeros are not significant.Captive Zeros are significant.Trailing Zeros are not significant

unless there is a decimal point.Exact numbers are infinitely

significant.◦Known numbers (not measured)◦Counted numbers ◦Definitions

Count the Sigfigs!How many sigfigs are in each of the

following measurements?◦A sample of orange juice contains

0.0108 g of vitamin C.◦A forensic chemist in a crime lab weighs

a single hair and records its mass as 0.0050060 g.

◦The distance between two points was found to be 5.030 x 103 ft.

◦In yesterday’s bicycle race, 110 riders started but only 60 riders finished.

Count the Sigfigs!How many sigfigs are in each of

the following measurements?◦0.00100 m◦2.0800 x 102 L◦480 Corvettes◦1,200 ft2

◦200. kg

Rounding and Sigfigs… In general for rounding…

◦ If the number following the last sigfig in the answer is greater than or equal to 5, round it up.

◦ If the number following the last sigfig in the answer is less than 5, it does not round up.

DO NOT ROUND ANY ANSWERS UNTIL YOUR FINAL STEP IN THE CALCULATION!!!!!!!!!!◦Helpful Hint: Learn how to use the store

and recall buttons on your calculators.

Rounding PracticeRound each of the following to 2

significant figures:◦4.592◦433◦658,493◦50,098◦5.96 x 103

◦0.004924◦1.999 x 10-4

Significance in CalculationsMultiplication & Division

◦The number of sigfigs in the result will have the same number of sigfigs as the LEAST precise measurement used in the calculation.

Addition & Subtraction◦The result will have the same

number of decimal places as the least precise measurement used in the calculation.

Practice: Sigfigs in Calculations

Give each answer with the correct number of sigfigs:

◦5.19 + 1.9 + 0.842 = ◦1081 – 7.25 = ◦2.3 * 3.14 = ◦83.024 / 1.50 = ◦124.86 – 73.9 = ◦154.8 – (18 + 23.9) = ◦(2.68 – 3.2) / (5.38 + 10.1) =

Practice: Sigfigs in Calculations

Give each answer with the correct number of sigfigs:

◦5.18 * 0.0208 = ◦ (3.60 * 10-3) * (8.123) / 4.3 = ◦21 + 13.8 + 130.36 = ◦116.8 – 0.33 = ◦ (1.33 * 2.8) + 8.41 = ◦12.6 * 0.53 = ◦ (12.6 * 0.53) – 4.59 = ◦ (25.36 – 4.15) / 2.317 =