The Scientific Method & Experimental Design Integrated Science: Intro to Physics Prepared by Mr....

The Scientific Method & Experimental Design

Integrated Science: Intro to PhysicsPrepared 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?04/20/23 Intro to Physics: Scientific Inquiry 2

04/20/23 Intro to Physics: Scientific Inquiry 3

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.

04/20/23 Intro to Physics: Scientific Inquiry 4

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)

04/20/23 Intro to Physics: Scientific Inquiry 5

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 = 1.604 km

1.604 km1mim

= 6.23 mi

Flashback

• Convert 87 cm into m using the Factor-Label technique using conversion units and cancelling units.

o (1 cm = 10-2 m)

04/20/23 Intro to Physics: Scientific Inquiry 9

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

04/20/23 Intro to Physics: Scientific Inquiry 10

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

04/20/23 Intro to Physics: Scientific Inquiry 11

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.04/20/23 Intro to Physics: Scientific Inquiry 12

Making Hypotheses!

• Complete all questions, in groups if you want.

04/20/23 Intro to Physics: Scientific Inquiry 13

Analyzing VariablesHeight (cm) Shoe Length (cm) Wingspan (cm) Stride Length (cm)

04/20/23 Intro to Physics: Scientific Inquiry 14

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?

04/20/23 Intro to Physics: Scientific Inquiry 15

Preview of this week:

• Today:– laboratory safety, scientific notation

• Tuesday:– Charts & Graphs

• Wednesday– Accuracy, precision, sig figs

• Thursday– Review

• Friday– Exam on Scientific Inquiry

04/20/23 Intro to Physics: Scientific Inquiry 16

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.

04/20/23 Intro to Physics: Scientific Inquiry 17

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.

04/20/23 Intro to Physics: Scientific Inquiry 18

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.

04/20/23 Intro to Physics: Scientific Inquiry 19

Stop to Think…

• Which of the following are allowed in the lab?

04/20/23 Intro to Physics: Scientific Inquiry 20

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)

23,471,693,273.2 3471693273 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

1010

Stop to Think…

• Place the following numbers into scientific notation.– 93,000,000– 3,600– 0.00015– 0.453– 152– 63– 9

Metric Prefixes

PowerPower PrefixPrefix SymbolSymbol Power Power PrefixPrefix SymbolSymbol

1010-18-18 atto-atto- aa 101011 deka-deka- da*da*

1010-15-15 femto-femto- ff 101022 hecto-hecto- h*h*

1010-12-12 pico-pico- pp 101033 kilo-kilo- kk

1010-9-9 nano-nano- nn 101066 mega-mega- MM

1010-6-6 micro-micro- µµ 101099 giga-giga- GG

1010-3-3 milli-milli- mm 10101212 tera-tera- TT

1010-2-2 centi-centi- cc 10101515 peta-peta- P*P*

1010-1-1 deci-deci- dd 10101818 exa-exa- E*E*

* rarely used

The Nature of Measurement

• Consider the following reading on a meter stick:

cm1 2 3 4 5 6 7 8

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

xxx

xxxx

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

xx

x

x

Neither accurate nor precise!

Precision vs. Accuracy

xx

xxxxx

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

04/20/23 Intro to Physics: Scientific Inquiry 31

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 1.600 g, then record 1.600 g, not

1.6 g.

04/20/23 Intro to Physics: Scientific Inquiry 32

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

04/20/23 Intro to Physics: Scientific Inquiry 34

Stop to Think

• What is the correct measurement for the length of the blue rectangle?

04/20/23 Intro to Physics: Scientific Inquiry 35

cm1 2 3 4 5 6 7 8

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!

04/20/23 Intro to Physics: Scientific Inquiry 36

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 - 378 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 822.6 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 17,500.06 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

04/20/23 Intro to Physics: Scientific Inquiry 48

Metric Prefixes

PowerPower PrefixPrefix SymbolSymbol Power Power PrefixPrefix SymbolSymbol

1010-18-18 atto-atto- aa 101011 deka-deka- da*da*

1010-15-15 femto-femto- ff 101022 hecto-hecto- h*h*

1010-12-12 pico-pico- pp 101033 kilo-kilo- kk

1010-9-9 nano-nano- nn 101066 mega-mega- MM

1010-6-6 micro-micro- µµ 101099 giga-giga- GG

1010-3-3 milli-milli- mm 10101212 tera-tera- TT

1010-2-2 centi-centi- cc 10101515 peta-peta- P*P*

1010-1-1 deci-deci- dd 10101818 exa-exa- E*E*

* rarely used