SCIENTIFIC METHOD observations questions hypotheses experimentation conclusions theories What you see… Pet dog going crazy scratching himself What you ask… “I keep a clean house, so why’s he scratching?” Educated guess… “He has fleas.” or “He has dry skin.” or… Test the Hypothesis… Buy Pluto a flea- collar Control: Pluto without a flea collar Treatment: Pluto with a flea collar Replication!!! 30 Plutos! Interpret your experimental results… No more scratching, your carpet is a flea graveyard! a hypothesis supported by repeatable evidence, Scratching Dog Theory: Dogs that scratch have fleas But Remember…. conclusions either reject or support hypothesis, never prove it! (have we ruled out dry skin??)

Allows us to study causation Not just correlation Lab studies Field studies experimental (treatment) group… The treatment where you manipulate the variable of interest Control Group Do every thing you did in the experimental group… ….except, leave out the variable of interest Do analysis (usually use stats.)

Scientific Measurements

Uncertainty in Measurement Many properties of matter are quantitative: –Associated with a number. –Units used in science are the metric system. SI Units: –Today’s system developed in 1960.

Physical Quantities Powers of ten are used for convenience with smaller or larger units in the SI system.

Prefixes Need to memorize some of the above selected prefixes and be able to convert from one prefix to another.

Temperature Fahrenheit: Define 32 o F as the freezing point of water and 212 o F as the boiling point of water at sea level. Kelvin: Define 0K as the lowest attainable temperature of o C (absolute zero). Don’t use o K.

Volume

The Density Concept Each cube represents a volume of 1 cm 3. As the mass increases, the density increases.

We will figure out the density of zinc in lab Density: –Used to characterize substances. –Defined as mass divided by volume: Units: g/cm 3, g/mL, g/L. Density of water is 1.00 at 25 0 C. Density is temperature dependent!

Volume by Displacement The difference between the initial and final water levels is equal to the volume of the solid jade.

Volume by Displacement The volume of water displaced is equal to the volume of oxygen gas produced by the sample.

Precision and Accuracy in measuring the density of zinc Precision: –How closely individual measurements agree with one another. Accuracy: –How closely individual measurements agree with the correct value.

Heat and Specific Heat Heat measures the total energy of a system. Temperature measures the average energy of a system. Specific Heat – Amount of heat (in calories) necessary to raise the temperature of 1g of any substance by 1 o C.

Heat and Specific Heat Each cube represents 1 g of substance receiving 1 cal of heat. The temp. change varies with the substance.