The Scientific Method

Science relies on facts, not opinions. is not static or fixed. Science is a process that changes as observations & measurements of new data are made.

There are 2 kinds of scientific studies: observational (usually done in the field) & controlled experiments (usually done in a lab)

Observational studies gather data or use existing data. not an experiment!! can support or refute a hypothesis. e.g. “Ring of Fire” is an observation that supports Theory of Plate Tectonics

Steps of the Scientific Method:

1. Observations-using any of the senses to detect a problem, issue, or just something that you can’t explain. e.g. In 1976, a deadly and contagious human disease appeared in several villages in Zaire (now the Democratic Republic of Congo).

Your observations lead you to come up with a… 2. Hypothesis –a possible explanation for what has been seen and recorded, a testable statement e.g. The disease is caused by a microorganism, such as a virus or bacterium.

Hypotheses are often written in “if/then” statements… “If I apply more fertilizer, then the tomato plants will produce larger tomatoes.” “If the fever, bleeding, and death is caused by the virus isolated from victims’ blood, then it will kill monkey cells in culture.”

How do you figure out if your hypothesis is correct?

3. Design a Controlled Experiment

What are the elements of a controlled experiment?

A controlled experiment uses subjects & variables

Test subjects Randomly divide the subjects into 2 groups: experimental group and control group. Test tubes containing monkey kidney cells were divided into 2 groups.

Both groups are treated exactly the same, except one group is treated with an independent variable. Drops of blood from a victim of the disease were added to the experimental tube ONLY.

So, the experimental group receives the treatment, but the control group does not. You need the control group for comparison. How do you know that the treatment had any effect unless you compare it to something?

There are 2 kinds of variables: independent & dependent

The Independent variable is the treatment given to the experimental group. e.g. 0.5 grams fertilizer for the tomatoes in the experimental group.

The Dependent Variable is/are the results of the treatment the dependent variable DEPENDS on the independent variable. e.g. Eleven days after the blood was mixed with the monkey cells, the cells in the experimental tube were dead. e.g. The tomatoes in the experimental group weigh 10 grams more on average than the control group.

4. Collect Data

There are 2 types of data

e.g. The watermelon weighs 5 kg. Quantitative data uses numbers

Qualitative data uses descriptions e.g. The watermelon is big.

Hint: remember quantity is in the quantitative data

5. Analyze Data

Data must be analyzed for experimental error Error can be caused by variation found in nature: e.g. argiope spiders don’t all catch the same quantity of prey e.g. tarantulas can have legs of different lengths, perhaps influencing their rate of travel

Error can be caused by imprecise measurement e.g. the units marked on the ruler are too large (hint: get a better ruler) e.g. the end of the ruler is shaved off (hint: get a better ruler, or make adjustments)

Data should be precise Precise date is consistent, It is reproducible or repeatable, and It should have small variance. Precise data is reliable need “a precise tool” (ruler, balance, graduated cylinder, etc.) +/-

Data should be accurate accurate data is “near” the true value, and measures what it’s supposed to measure. accurate data is valid accurate data has been measured over and over

Measurements can be precise but not accurate. e.g. you keep getting the same ozone readings over and over, but your instruments are not taking into account the humidity, so the readings are all wrong

After the results have been analyzed and conclusions have been made… 6. Report the results in a scientific journal in a press conference as a keynote speaker at a convention e.g. Scientists from the CDC and the WHO wrote-up and published their findings.

Does your experiment support or refute your hypothesis? If refutes, then write another hypothesis. 7. What’s next?

If your data supports your hypothesis… Have you created a new scientific theory or law? Probably not, but you may have new evidence that supports a theory!

8. A Scientific theory is a grand explanation. is generally regarded as true. is never proven but can be disproved. is continually supported by evidence & experiments. e.g. Cell Theory, Theory of Relativity, Theory of Evolution

9. A Scientific law describes how things happen. is continually supported by evidence & experiments. e.g. Newton’s 2 nd Law of motion, Laws of Thermodynamics

10. A Scientific Model is a deliberately simplified construct. has value in a general way, but usually lacks the detail and intricacy of nature. e.g. computer models of weather patterns, DNA models, models of the atom