The Scientific Method

Objectives

Define the scientific method.

Compare the 4 parts of the experimental

procedure.

Science as a Process of Inquiry

Science is a way of knowing - a human endeavor emerging from our curiosity about ourselves, the world, and the universe.

Good scientists:

1) question nature, believing that answers can be found to their questions; 2) are curious, observant, and passionate about their quest for discovery; 3) are creative & often skeptical.

Science as a Process of Inquiry

Scientific method: process outlining steps to answer a question.∙ Not a rigid procedure. ∙ Based on a conviction that phenomena have natural causes. ∙ Requires evidence to logic-

ally solve problems. Ask a question, and form-

ulate a hypothesis. Make predictions from the

hypothesis, and then test the validity of the predictions.

• Lastly, make a conclusion

✓✓✓

✓

Science as a Process of Inquiry

Scientific method:∙ Observation – step 1 –

An observant person notices something

unexpected that can’t be simply explained. Being curious, he orshe has a question

and must investigate.∙ Hypothesis – step 2 –

He or she attempts to explain the observation.

• Lastly, make a conclusion

✓✓

Science as a Process of Inquiry

Hypothesis: a testable explanation for an observation.Greek root words: hypo = beneath & thesis = idea or plan. so.. hypothesis means the underlying idea or reason why.

Useful hypotheses also have the following characteristics: ∙ reflect past experience, not blind guesses; ∙ must be testable by the scientific method; ∙ can be eliminated but not confirmed with absolute

certainty. Confidence increases with repetition. ∙ more than one hypothesis should be proposed for an

observation since one alone might bias or restrictthe search for evidence.

Hypothesis and Prediction

Prediction: what to expect if the hypothesis is correct (stated as if…then). Comes after completion of work.

A so-so hypothesis and prediction: Plants need Mg to remain healthy; therefore, if I withhold Mg then the plant will die. (How to test health?)

A better hypothesis and prediction: (based on research)Plants need Mg to stay green; therefore if I withhold Mg then the plant will yellow (because Mg is an im-portant component of chlorophyll, the green pigment).

Measure color.Measure color.

Hypothesis vs. Theory

Hypothesis: underlying idea for an experiment. A hypo-

thesis must be testable. Ex: the Earth is flat.

Theory: a collection of related hypotheses, which have been

tested and supported by experimentation. A theory

cannot be directly tested. Ex: Theory of Evolution,

Big Bang Theory.

Science as a Process of Inquiry

Scientific Method:∙ Experiment – step 3: a controlled test of a hypothesis designed to investigate the effect of only one variable.

Variable: a factor or condition, subject to change, that influences the outcome of an experiment. Example: in an experiment testing the growth of plants, the amount of sunlight, fertilization, and water are independent variables that affect plant growth (the dependent variable).

Growth Growth dependsdepends on water, etc. on water, etc.

An experiment has 2 groupings: 1) the experimental group – with one special extra

variable.2) the control group - the variable is missing, all else same.

Science as a Process of Inquiry

The experimental plan is a subset of the Scientific Method and an elaboration; it includes four parts, or headings, for set-ting up and writing the experiment:

1) Hypothesis - the underlying idea or plan. 2) Set-up - organizing the materials & preparing

the methods. 3) Collecting and analyzing the data - the results. 4) Forming a conclusion - the results either agree

with your hypothesis, or if they disagree then you must make a new hypothesis.

Example of an experimental plan

Hypothesis: Plants need magnesium to stay green.M & M: A control group gets no magnesium fertilizer.

An experimental group gets magnesium added to the soil (all other indep. variables [water, light, etc.] are the same). Replication: Due to variability, use 4 or more plants / group.

Results: Measure leaf color weekly with color chart.Control plants become yellow after 3 weeks,

but the other plants stay green.Conclusion: Plants need magnesium to stay green.

Next question: What makes plants green? A pigment or what?

Example of an experimental plan

Materials & Methods: Fully describe every detail of the set-up so another person would be able to copy the plan exactly.

Plants used: their common and scientific names. Chemicals used: their concentrations, and their source. Soil type and source; pot size; air temperatures. Light source and amount. Water: amount and how often. Sample size: at least 4 samples per treatment.

Example of an experimental plan

Results: Analyze the data Describe results in words; use tables & graphs to help

explain There must be a statistical evaluation of the data to show

that it is truly valid; compare means not individual samples.

If error bars overlap, there is no real difference in the means.

Science as a Process of Inquiry

Scientific Method:∙ Conclusion – step 4: Is the hypothesis supported by the investigation; can it be justified? ∙ Is the result due to chance or random error? ∙ This is the reason for replication – to be sure.∙ Statistics are necessary to be convincing. ∙ Must be ~95% certain, or do more work. ∙ What are weaknesses of the work?∙ Poor replication, data collection, or plan? ∙ How could the work be improved? ∙ What is the value of the work to others?

The Scientific Method