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.