Scientific Method Is a Logical Approach to Solving Problems and Collecting Data, Formulating

Chapter 2 Notes

2-1 Scientific Method

Scientific method is a logical approach to solving problems and collecting data, formulating a hypothesis, testing hypotheses and formulating theories that are supported by data.

Observing and collecting data

Ø Data may be descriptive (qualitative) or numerical (quantitative).

Ø A system is a specific portion of matter in a given region of space that has been selected for study during an experiment of observation.

Formulating hypotheses

Ø Scientists make generalizations about data

Ø From this information, a hypothesis (testable statement) is formed.

Ø “If…then…” statement

Testing hypotheses

Ø Requires experimentation

Theorizing

Ø A model is used to try to explain the phenomena

Ø Model- an explanation of how phenomena occur and how data or events are related. Shows how things work

Ø Models may be visual, mathematical or verbal

Ø Models lead to theories

Ø Theory-broad generalization that explains a body of facts or phenomena

Ø Successful theories predict the results of new experiments.

2-2 Units of measurement

Ø Measurements are quantitative.

Ø Measurements represent quantities.

Ø A quantity is something that has magnitude, size or amount.

Ø A unit of measurement is what we measure quantity in.

Quantity would be mass

Unit would be kilogram

Ø There must be agreement on measurements to avoid confusion.

SI Measurement

Ø Scientists agree on Le Systeme International d’Unitese. (SI)

Ø SI units are defined in terms of standards of measurement

Ø SI units are defined in terms of standards of measurement that are easy to preserve, reproduce and are practical in size.

Ø We do not use commas, but spaces every three digits both to the right and the left of the decimal point.

SI Base Units

Seven base units are listed on p. 34

SI prefixes are listed on p. 35

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Mass

Standard SI unit of mass is the kilogram (Kg)

Mass is determined by comparing the mass of one item to the known mass of another.

Weight is not mass.

Weight is the measure of gravitational pull on matter

Mass does not depend on gravitational attraction

Length

Standard unit of length is the meter (m).

Kilometer (1 000 m) is used for longer lengths.

Centimeter (0.01 m) is used for shorter lengths

Derived SI units

Derived SI units are produced by multiplying and/or dividing standard SI units.

Meters x meters = meters2

kilograms/meters x seconds x seconds = kg/ms2 = a Pascal, Pa

Volume

Volume is the amount of space an object occupies

A m3 = 1 000 000 cm3

1 mL = cm3

Density

Density is the mass to volume ratio of a material.

Density = mass/volume or D=m/v

Standard units are Kg/m3

Not convenient, so g/cm3 is used

Density is a characteristic property

Density does not depend on the amount of matter

The density of water is 1 gram/cm3

When a substance is less dense than another, the less dense substance floats in the other liquid

*Sample problem p. 39

*Do practice problems 1-3 p. 40

Conversion factors

A conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to another.

Conversion factors are equal to one, so they can be multiplied by a number and retain the same value.

Our goal is to convert to desired units.

Set up your problem based on units first.

(You may use more than one conversion factor at a time.)

Deriving Conversion Factors

An equality may be expressed as a ratio (fraction) equal to one.

1 meter = 100 centimeters

100 cm

This may be a conversion factor

It may also be expressed as:

100 cm

1 m

To convert 19 cm into m, use the conversion factor to get desired units:

19 cm x 1m = ______m

100 cm

*Sample problem 2-2 p. 41 *Practice problems 1-2 p. 42

2-3 Using Scientific Measurements

Accuracy-closeness to an accepted value

Precision-closeness of a set of measurements

% error = (Valueaccepted – Valueexperimental) / Valueaccepted x100%

Significant figures consist of all values that are known with certainty and one last doubtful, or estimated digit. See rules p. 47

Round as usual

When adding or subtracting, the answer must have the same numbers to the right of the decimal as in the number with the least numbers to the right of the decimal

When multiplying and dividing, the answer can have only as many digits as the number with the least significant digits.

Conversion factors are considered to be exact and have an indefinite nimber of significant digits.

Scientific notation numbers are written in the form of M x 10n

M is > or = 1 and <10

Determine M:

Move the decimal point to the left or right so only one nonzero digit is to the left of the decimal point.

Determine n:

Count the number of places that you moved the decimal; if you moved the decimal to the right, n is negative; if you moved the decimal to the left, n is positive

To add or subtract in scientific notation:

Make both exponents (n) the same

Perform the given calculation on M

To multiply or divide in scientific notation:

Perform the given calculation on M

For multiplication, add the exponents

For division, subtract the exponents

Direct proportions:

y/x=k

y=kx

k is a constant value

divide one value by another and get a constant value

Inverse proportions:

Y 1/x

Xy=k

Products are constant