UNIT I Experimental

Design

I. What is Science

A. Goal of Science -

1. Deals only with natural world.

2. Scientists collect and organize information in careful, orderly way, looking for patterns and connections between events.

3. Scientists propose explanations that can be tested by examining evidence.

4. Evidence based on Observation

a. Observation involves one or more senses (sight, hearing, touch, smell, taste) to gather information

b. Information gathered is called evidence (data)

c. Observation classified into two types:

1). Quantitative– involve numbers, counting, measuring objects.

2). Qualitative– involve characteristics that cannot be easily measured or counted such

as color or texture

Good Example of qualitative performance being converted into quantitative data. Not science!

Iraqi High Diving Olympics

B. How Scientists Work: The Scientific Method (common steps scientists take to gather information and answer questions)

1. Observing and Stating a Problem- process of science always starts with an observation

2. Forming a Hypothesis– a possible explanation, a preliminary conclusion, or even a “educated” guess about some event in nature.

3. Testing Hypothesis– In science, testing hypothesis often involves designing an appropriate experiment.

Hypotheses must be testable – not questions like “is there a God” or “how beautiful is this”.

a. Setting up controlled experiment

1). Experiment involves several variables (factors that change).

•Independent variable – the variable that is manipulated in an experiment.

•Dependent variable – the variable that is changed, due to the changing of the independent variable.

Usually, you would place your independent variable on the x-axis of your graph and the dependent variable on the y-axis.

a. Setting up controlled experiment

2). Controlled experiment– tests effect of a single variable while keeping all other variables the same (controlled variables).

3). Any observed differences should be caused only by the single changed variable

4). If possible, it would be best to use a control group to compare results to.

b. Francesco RediFrancesco Redi (1600’s)- designed one of the first controlled experiments

1). Redi designed an experiment to determine what caused the appearance of maggots on meat

Not in notes

2). Hypothesized that would not appear if kept flies away from meat.

3). Planned controlled experiment and controlled all variables except one.

Controlled variables: jars, type of meat, location, temperature, time

Experimental variable: gauze covering that keeps flies away from meat

4). Helped to disprove prevailing hypothesis of origin of life (spontaneous generation- “life from non-living things)

c). Louis Pasteur (1864)- tried to settle argument for spontaneous generation.

Some said that air was necessary for Spontaneous generation.Pasteur’s experiment showed that boiled broth would remain free of microorganisms even if air was allowed in, as long as dust and other particles were kept out

Why did microorganisms grow after Pasteur broke the neck of the flask?

Curved neck removed

Broth is teeming with microorganismsBroth is boiled

Both is free of microorganisms for a year

4. Recording and Analyzing Results– scientist usually keep written records of observations they make– called data.

1. Data are organized in graphs and charts.

2. Detailed written notes are kept in notebooks.

5. Drawing a Conclusion– scientist use data from experiment to evaluate the hypothesis and draw conclusion

a. If wrong, form new hypothesis

b. A key assumption in science is that

experimental results can be reproduced because nature behaves in a consistent manner

6. Inference– The act of reasoning from factual knowledge or evidence.

***This is what scientists do with observations and data – infer from evidence.

Designing an Experiment

• How could you decrease a person’s blood pressure?– Hypothesis:

– Control:

– Dependent variable:

– Independent variable: