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Scientific Method A method of solving
problems/answering questions Observation- what is seen or measured Hypothesis- educated guess of why
things behave the way they do. (possible explanation)
Experiment- designed to test hypothesis leads to new observations, and the cycle goes on
Scientific Method Theory (Model)Theory (Model)
– A set of tested hypotheses that give an overall A set of tested hypotheses that give an overall explanation of some natural phenomenon why things explanation of some natural phenomenon why things behave the way they dobehave the way they do
– explains why something happensexplains why something happens
LawLaw– The same observation applied to many different The same observation applied to many different
systemssystems– Example - Law of Conservation of Example - Law of Conservation of MassMass
Laws are summaries of observationsLaws are summaries of observations
Scientific Method Theories have predictive value. The true test of a theory is if it can
predict new behaviors. If the prediction is wrong, the theory
must be changed. Theory- why Law - how
Significant Figures Meaningful digits in a MEASUREMENT Exact numbers are have unlimited
significant figures If it is measured or estimated, it has sig.
figs.
All numbers except zero are significant. Some zeros are, some aren’t
Which zeroes count?
ZerosZeros
leading zerosleading zeros
captive zeroscaptive zeros
trailing zerostrailing zeros
3200 2 sig figs
3200. 4 sig figs
Which zeroes count?
ZerosZeros
Captive zerosCaptive zeros always count always count as significant figures. as significant figures.
16.07 16.07 hashas
4 4 sig figs.sig figs.
Which zeroes count?
ZerosZeros
Trailing zerosTrailing zeros are significant are significant
only if the number containsonly if the number contains
a decimal point.a decimal point.
9.3009.300 has has
44 sig figs. sig figs.
Which zeroes count?
Exact numbersExact numbers have an infinite have an infinite number of significant figures.number of significant figures.
11 inch = inch = 2.54 2.54 cm, exactlycm, exactly
Doing the mathMultiplication and division
# sig figs in the result equals the # sig figs in the result equals the number in the least precise number in the least precise measurement used in the calculationmeasurement used in the calculation
6.38 6.38 2.0 = 2.0 =
12.76 12.76 13 (2 sig figs)13 (2 sig figs)
Doing the mathAddition and subtraction
# sig figs in the result equals the # sig figs in the result equals the number of decimal places in the least number of decimal places in the least precise measurement.precise measurement.
6.8 + 11.934 =6.8 + 11.934 =
22.4896 22.4896 22.5 (3 sig figs)22.5 (3 sig figs)
SI Measurement System Every measurement has two parts
– Number
– Scale (unit) SI system (le Systeme International) based
on the metric system
– Prefix + base unit
– Prefix tells you the power of 10 to multiply by - decimal system -easy conversions
Prefixes giga- G 1,000,000,000 109
mega - M 1,000,000106
kilo - k 1,000 103
deci-d 0.1 10-1
centi- c 0.01 10-2
milli- m 0.001 10-3
micro- 0.000001 10-6
nano- n 0.000000001 10-9
Mass and Weight Mass is measure of resistance to
change in motion Weight is force of gravity. Sometimes used interchangeably Mass can’t change, weight can
Uncertainty A digit that must be estimated is called
uncertain. A measurement always has some degree
of uncertainty Basis for significant figures Precision- how repeatable Accuracy- how correct - closeness to true
value.
Uncertainty
Random error - equal chance of being high or low- addressed by averaging measurements - – expected in all measurements
Systematic error- always the same direction each time – you want to avoid this type of error
you can have precision without accuracy You can’t have accuracy without precision
Dimensional Analysis Use conversion factors to change the units Conversion factors = 1 1 foot = 12 inches (equivalence statement) 12 in = 1 = 1 ft.
1 ft. 12 in
2 conversion factors multiply by the one that will give you the
correct units in your answer.
Examples
Science fiction often uses nautical analogies to describe space travel. If the starship U.S.S. Enterprise is traveling at warp factor 1.71, what is its speed in knots?
Warp 1.00 = 5.00 times the speed of light speed of light = 3.00 x 108 m/s 1 knot = 2000 yd/h exactly
Temperature A measure of the average kinetic
energy Different temperature scales, all are
talking about the same height of mercury.