The Scientific Method

Question Well defined Testable Measurable Controllable Reasonable and consistent with existing bodies of knowledge

Consider These Questions Are serial killers evil by nature? What is the cause of AIDS? Why is grass green? What is the best recipe for chocolate chip cookies? When will the big earth quake hit San Francisco?

Hypothesis Testable Falsifiable Written as a statement

Which of the following is a useful scientific hypothesis? Plants absorb water through their leaves as well as their roots. Mice require calcium for developing strong bones. Dogs are happy when you feed them steak. HIV can be transmitted by cat fleas.

Variables Dependent The variable measured, counted, or recorded. Placed on y-axis of a graph Independent What the investigator deliberately varies or manipulates during an experiment. Chosen because it is thought to affect the dependent variable Placed on x-axis of graph Control Variables or factors that are kept equal in all treatments.

Identify the D and I variables Height of a bean plant recorded daily for 2 weeks. Mice are kept at different temperatures for 6 weeks. Percent weight gain is recorded. A hypothesis proposes that dog weight increases with fewer litter mates. Seeds are soaked in salt solutions of different concentrations and germination is counted each day. The diversity of coastal algal species is calculated before and after an oil spill.