Observing and Collecting Data

• Observing is the use of the senses to obtain information.

• data may be • qualitative (descriptive)• quantitative (numerical)

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

Chapter 2

HypothesisHypothesis

Scientists make generalizations based on the data.

Scientists use generalizations about the data to formulate a hypothesis, or testable statement.

Hypotheses are often “if-then” statements

Experimental DesignExperimental DesignTesting a hypothesis requires Testing a hypothesis requires

experimentation that provides data to experimentation that provides data to support or refute a hypothesis or theory.support or refute a hypothesis or theory.

Controls Controls are the experimental conditions are the experimental conditions that remain constant.that remain constant.

Variables Variables areare any experimental conditions any experimental conditions that change.that change.

Experimental DesignExperimental Design Independent variable – is the manipulated Independent variable – is the manipulated

variable or the variable that the variable or the variable that the experimenter changes.experimenter changes.

The dependent variable – is the variable The dependent variable – is the variable that changes due to the independent that changes due to the independent variable.variable.

Graphing – we put the independent Graphing – we put the independent variable on the X-axis and the dependent variable on the X-axis and the dependent variable on the y-axisvariable on the y-axis

SI UnitsSI UnitsSI units of measure are the accepted units SI units of measure are the accepted units

of measure for science.of measure for science.The SI unit is based on multiples of 10.The SI unit is based on multiples of 10.

Mass is a measure of the quantity of matter.

The SI standard unit for mass is the kilogram.

Weight is a measure of the gravitational pull on matter.

Mass does not depend on gravity

Length is a measure of distance.

The SI standard for length is the meter.

The kilometer, km, is used to express longer distances

The centimeter, cm, is used to express shorter distances

Combinations of SI base units form Combinations of SI base units form derived units.derived units. pressure is measured in kg/m•s2, or pressure is measured in kg/m•s2, or pascalspascals

DensityDensity is the ratio of mass to volume, or is the ratio of mass to volume, or mass divided by volume.mass divided by volume.

density =

massvolume

or D = mV

•The derived SI unit is kilograms per cubic meter, kg/m3

•g/cm3 or g/mL are also used

Accuracy and PrecisionAccuracy and PrecisionAccuracy refers to the closeness of

measurements to the correct or accepted value of the quantity measured.

Precision refers to the closeness of a set of measurements of the same quantity made in the same way.