The Scientific Method & Experimental Design Integrated Science: Intro to Physics Prepared by Mr. D. McCallister Modified by Mr. R. Moleski, Ph.D.

The Scientific Method Ask a question Research the Subject – Library Research that is Formulate a Hypothesis Design and conduct the Experiment Collect and Analyze data Make a tentative Conclusion Test the Conclusion Repeat the Experiment…….Why? 10/25/2015Intro to Physics: Scientific Inquiry2

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Variables Properties that change during an experiment Can be – Independent this variable is changed by the experimenter – Dependent this variable changes because of the independent variable All other properties should be held constant- they are called Controlled Variables. 10/25/2015Intro to Physics: Scientific Inquiry4

Units of Measure Original Metric Units – Distance – meter (m) – Time – seconds (s) – Mass – kilograms (kg) SI Units (these 7 are the basis for all others) – Temperature – kelvins (K) – Electric Current – ampere (A) – Light Intensity – candela (cd) – Amount of a Substance – mole (mol) 10/25/2015Intro to Physics: Scientific Inquiry5

Dimensional Analysis & Unit Conversion

What is dimensional analysis? A tool that allows us to change units and solve problems.

10 km = ?? mi 10 km ( ) ___________ 1 mi = km km 1mi m = 6.23 mi

Flashback Convert 87 cm into m using the Factor-Label technique using conversion units and cancelling units. o (1 cm = m) 10/25/2015Intro to Physics: Scientific Inquiry9

Terms, terms, terms… fact – a close agreement by competent observers who make a series of observations of the same phenomenon. – revisable data about the world laws (a.k.a. principles) – hypotheses and facts that are tested over and over again without being contradicted – not as descriptive as theories 10/25/2015Intro to Physics: Scientific Inquiry10

Terms, terms, terms… theory – a synthesis of a large body of information – not judged as “true or not true,” rather as “useful or not useful” – interpret facts concept – intellectual framework that is part of a theory 10/25/2015Intro to Physics: Scientific Inquiry11

Terms, terms, terms… hypothesis – an educated guess – to be scientific hypothesis, must be testable – must have a test for rightness, and a test for wrongness – Which of the following are scientific? The universe is surrounded by a second universe, the existence of which cannot be detected by scientists. Albert Einstein was the greatest physicist of the twentieth century. Atoms are the smallest particles of matter. 10/25/2015Intro to Physics: Scientific Inquiry12

Making Hypotheses! Complete all questions, in groups if you want. 10/25/2015Intro to Physics: Scientific Inquiry13

Analyzing Variables Height (cm)Shoe Length (cm)Wingspan (cm)Stride Length (cm) 10/25/2015Intro to Physics: Scientific Inquiry14

Review of Last Week Tuesday: What is physics? – the study of the interactions of mass and energy Wednesday: Scientific Method, Units of Measure, Factor Label – length (meter), time (second), mass (kilogram) – metric prefixes – converting between units using factor-label Thursday: Making Hypotheses – theories, facts, laws Friday: Analyzing Variables – Was there a relationship between height and other body characteristics? 10/25/2015Intro to Physics: Scientific Inquiry15

Preview of this week: Today: – laboratory safety, scientific notation Tuesday: – Charts & Graphs Wednesday – Accuracy, precision, sig figs Thursday – Review Friday – Exam on Scientific Inquiry 10/25/2015Intro to Physics: Scientific Inquiry16

Laboratory Safety Procedures Wear the right clothing for lab work. – No open-toe shoes! Do not perform unauthorized experiments or use equipment and apparatus in a manner for which they were not intended. No horseplay in the lab. Never work alone in the lab. Follow fire drill procedures when fire alarm sounds. 10/25/2015Intro to Physics: Scientific Inquiry17

Fire Alarm Procedures Exit the room and turn right, then left to exit the building near the main office. Meet the class halfway down the parking lot on the right. 10/25/2015Intro to Physics: Scientific Inquiry18

Electricity Lab Safety Procedures Do not use electrical equipment with frayed or twisted wires. Be sure your hands are dry before using electrical equipment Do not trip over electrical cords. Use extreme caution when working with hot plates or other heating devices. 10/25/2015Intro to Physics: Scientific Inquiry19

Stop to Think… Which of the following are allowed in the lab? 10/25/2015Intro to Physics: Scientific Inquiry20

This number becomes the exponent of ten. Moving the decimal left makes it positive, right makes negative. Scientific Notation Is there an easier way to express large numbers? – Ex) 23,471,693, Move the decimal point so that there is only one non- zero digit on the left of it. Count the number of decimal places you moved the decimal point. places x 10 10

Stop to Think… Place the following numbers into scientific notation. – 93,000,000 – 3,600 – – – 152 – 63 – 9

Metric Prefixes PowerPrefixSymbolPowerPrefixSymbol atto-a 10 1 deka-da* femto-f 10 2 hecto-h* pico-p 10 3 kilo-k nano-n 10 6 mega-M micro-µ 10 9 giga-G milli-m tera-T centi-c peta-P* deci-d exa-E* * rarely used

The Nature of Measurement Consider the following reading on a meter stick: cm

Error Random – can be reduced with repeated readings Systematic – cannot be reduced with repeated readings – always in same direction (high or low)

Precision vs. Accuracy Accuracy is how close readings or calculations are to the true or accepted value. Precision is how many decimal places an instrument resolves. To illustrate this…. a challenge of archery!!!!

Precision vs. Accuracy True or accepted value x x x x x x x Precise, but not accurate!

Precision vs. Accuracy x x x x x x x x Accurate, but not precise!

Precision vs. Accuracy x x x x x x x Neither accurate nor precise!

Precision vs. Accuracy x x x x xx x Both accurate and precise!

So what’s the difference? Accuracy is how close a measurement is to the true or accepted value Precision is how close repeated measurements are to each other 10/25/2015Intro to Physics: Scientific Inquiry31

How many decimal points do I record? Always all the measured digits, and one estimated For graduated instruments (meter stick, spring scales) – Record to half the smallest marking (estimate 0.5 mm on a meter stick) For digital instruments – Record the measurement given, exactly as it is shown ex) If a digital scale reads g, then record g, not 1.6 g. 10/25/2015Intro to Physics: Scientific Inquiry32

Stop to Think… Which is more precise, the metric side of a meter stick or the inches side? What could affect the accuracy of a meter stick?

Sig Figs If numbers given in a problem aren’t precise, then our answer shouldn’t be either! There are rules for adding & subtracting sig figs – demonstration There are yet more rules for multiplying & dividing sig figs! – demonstration 10/25/2015Intro to Physics: Scientific Inquiry34

Stop to Think What is the correct measurement for the length of the blue rectangle? 10/25/2015Intro to Physics: Scientific Inquiry35 cm

Modeling It is often helpful to simplify real-world phenomena in order to understand it better. A model is a simplification of reality that allows us to understand a situation better. It is NOT real-life, but a simplification of real- life. In a word: models are SIMPLIFICATIONS! 10/25/2015Intro to Physics: Scientific Inquiry36

The Physics of Christmas A Great Example of Modeling

No known species of reindeer can fly. But there are 300,000 species of living organisms yet to be classified, and while most of these are insects and germs, this does not COMPLETELY rule out flying reindeer which only Santa has ever seen. Santa has 31 hours of Christmas to work with, thanks to the different time zones and the rotation of the earth, assuming he travels east to west (which seems logical).

There are 2 billion children (persons under 18) in the world. BUT since Santa doesn't (appear) to handle the Muslim, Hindu, Jewish and Buddhist children, that reduces the workload to 15% of the total million according to Population Reference Bureau. At an average (census) rate of 3.5 children per household, that's 91.8 million homes. One presumes there's at least one good child in each.

This works out to visits per second. This is to say that for each Christian household with good children, Santa has 1/1000th of a second to park, hop out of the sleigh, jump down the chimney, fill the stockings, distribute the remaining presents under the tree, eat whatever snacks have been left, get back up the chimney, get back into the sleigh and move on to the next house.

Assuming that each of these 91.8 million stops are evenly distributed around the earth (which, of course, we know to be false but for the purposes of our calculations we will accept), we are now talking about.78 miles per household, a total trip of 75-1/2 million miles, not counting stops to do what most of us must do at least once every 31 hours, plus feeding and etc.

This means that Santa's sleigh is moving at 650 miles per second, 3,000 times the speed of sound. For purposes of comparison, the fastest man- made vehicle on earth, the Ulysses space probe, moves at a poky 27.4 miles per second - a conventional reindeer can run, tops, 15 miles per hour.

The payload on the sleigh adds another interesting element. Assuming that each child gets nothing more than a medium-sized Lego set (2 pounds), the sleigh is carrying 321,300 tons, not counting Santa, who is invariably described as overweight.

On land, conventional reindeer can pull no more than 300 pounds. Even granting that 'flying reindeer' (see point #1) could pull TEN TIMES the normal amount, we cannot do the job with eight, or even nine. We need 214,200 reindeer. This increases the payload - not even counting the weight of the sleigh - to 353,430 tons. Again, for comparison - this is four times the weight of the Queen Elizabeth cruise ship.

353,000 tons traveling at 650 miles per second creates enormous air resistance - this will heat the reindeer up in the same fashion as spacecraft re-entering the earth's atmosphere. The lead pair of reindeer will absorb 14.3 QUINTILLION joules of energy. Per second. Each.

In short, they will burst into flame almost instantaneously, exposing the reindeer behind them, and create deafening sonic booms in their wake. The entire reindeer team would be vaporized within 4.26 thousandths of a second. Santa, meanwhile, will be subjected to a centrifugal effect that is 17, times greater than gravity. A 250-pound Santa (which seems ludicrously slim) would be pinned to the back of his sleigh by 4,315,015 pounds of force.

But all this is irrelevant, since Santa is magic!!!! THE END!!!! Tinyurl.com/mcphysics

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Metric Prefixes PowerPrefixSymbolPowerPrefixSymbol atto-a 10 1 deka-da* femto-f 10 2 hecto-h* pico-p 10 3 kilo-k nano-n 10 6 mega-M micro-µ 10 9 giga-G milli-m tera-T centi-c peta-P* deci-d exa-E* * rarely used