Scientific Methods

What is the Scientific Method?• There is not ONE scientific method.• Scientists approach and solve problems

with imagination, creativity, prior knowledge and perseverance. These, of course, are the same methods used by all problem-solvers.

• Scientists use different processes to solve different problems.

• In physics and chemistry, the experimental method is used because variables can be controlled.

Scientific Problem Solving

• Experiments are not the only method of problem solving.

• In some science disciplines, like astronomy, anthropology, and zoology, true experimentation is not possible because of not being able to control variables.

• Many fundamental discoveries in these areas are based on extensive observations rather than experiments.

Scientific knowledge is gained in a variety of ways including: ObservationAnalysisSpeculationLibrary investigationExperimentation

Let’s see how modern science began…

Beginnings

Aristotle • 384 BCE-322 BCE• An ancient Greek

philosopher

Aristotle• Aristotle was the author of a

philosophical and scientific system that through the centuries became the standard for both medieval Christian and Islamic scholarly thought.

• Until the end of the 17th century, Western culture was Aristotelian. And, even after many centuries, Aristotelian concepts and ideas remained embedded in Western thinking.

• In other words, Aristotle was so famous that his work influenced thinking in the Western world from his time to the present.

• This was fine when he was right. But he was so influential that his mistakes were never noticed.

• Aristotle and his contemporaries believed that all problems could be solved by thinking about them.

• Sometimes this worked, other times it did not.

• For example, Aristotle thought that heavy objects would fall faster than lighter ones.

• Now that does seem reasonable at first. Besides, this was how “science” was done in ancient times.

• But what did Aristotle not do?• He never tested his ideas!• The world would have to wait almost

2000 years for that to happen.

Galileo Galilei•1564-1642 CE

•Lived in what is today Italy

•Is considered to be the first true scientist.

•Why????

•Because he actually did the experiment.

• Aristotle said that heavy objects fall faster than lighter ones.

• So Galileo asked, “How much faster?”

• So he sent students up to the top of a building and had them drop off a heavy ball and a lighter one at the same time.

• He had other students waiting below to measure the difference in time between the two hitting the ground.

Today, of course, we know what happened.

Much to everyone’s surprise, both balls hit the ground at about the same time!

One test is worth a

thousand expert

opinions.

This shows that it is much preferred to test your ideas rather than merely think about them.

Experiment• An experiment is a planned way to test a

hypothesis and find out the answer to the problem statement.

• An experiment is a way to collect data and determine the value of the dependent variable.

• An experiment compares the independent variable to the dependent variable.

• An experiment can only test one dependent variable at a time.

Key Idea

• When conducting an experiment, change one factor and keep everything else exactly the same.

• The one thing you change is called the variable.

• All the things you keep the same are called controls.

Galileo’s Experiment

• What was the variable in Galileo’s experiment?

The weight of the balls• What were some controls? ∞ Dropped from same height ∞ Dropped at same time ∞ Balls had same shape

Example

A student decides to study the affect of caffeine on test performance. Five students drink caffeinated Pepsi and the other five drink caffeine-free Pepsi. They all took the same test the next day.

• What is the control?– The test

• What is the Independent Variable?– Caffeine or Caffeine-Free Pepsi

• What is the Dependent Variable?– Test Score

Scientific Method Steps

• Ask a question• Conduct background research• Construct a hypothesis• Test with an experiment• Record and analyze data• Communicate results so

others can repeat the experiment

Hypothesis• A prediction based on extensive study• May use an “If”, “then” format• “We predict that if we drop a ball from

a higher height, then it will bounce higher.

• The “If” statement is the manipulated variable.

• The “Then” statement is the responding variable.

Observations

• Observations: We use our senses to gather information about the world around us.

• There are two types of observations:

QualitativeQualitative observation: (quality)• Usually made with our senses

– Color, shape, feel, taste, sound

Examples:Olivia is wearing a blue sweater.The lab tabletop is smooth.The dog’s fur is shiny.

QuantitativeQuantitative observation: (quantity)•Tells how many •Will always have a number•Based on exact measurement

Examples:The room is 8 meters across.Sarah is 141-cm tall.Sam weighs 450 Newtons.

Inferences

Inference:• A logical

interpretation of an event that is based on observations and prior knowledge

What can you infer from this picture?

Making Inferences

You are at the counter in the office. You see a student leave the principal’s office crying and upset. You could make an inference as to why the student is upset.

• Could be in trouble (ISS, expelled)• Family problems (emergency, accident)• Student not feeling well• Student has poor grades (failing,

retention)

Theory

• Has a very different meaning in science than in everyday life.

• “The detective has a theory about who robbed the bank.” This is a guess.

• When scientists use the word theory it is not used as a guess.

Theory defined

• An explanation based on many observations during repeated experiments that is valid only if it is consistent with observations, makes predictions that can be tested, and is the simplest explanation.

• A logical, time tested explanation for events that occur in nature.

• So the theory of gravity, theory of electricity, the germ theory of disease, and the theory of evolution are tested, accepted explanations for events that occur in nature.

• Theories can really never be completely proven, only disproven. When new evidence comes along, we must modify our theory or, at times, even get rid of it and start over again.

• Ptolemy’s earth-centered theory of the solar system is an example of what can happen when new evidence comes along.

• When Copernicus showed that putting the Sun in the center made it much easier to predict the planets motions, the old earth centered theory was discarded and a new one developed.

Graphing

• Graphs are useful tools in science.

• The visual characteristics of a graph make trends in data easy to see.

• One of the most valuable uses for graphs is to "predict" data that is not measured on the graph.

Graphing Steps

• Give your graph a title

• Identify the Variables• Determine the range• Determine the scale• Number and label each axis• Plot the points

• Draw the graph

• Create a key

Identify the Variables

–Independent Variable - (the thing you changed) Goes on the X axis (horizontal) Should be on the left side of a data table.

–Dependent Variable - (changes with the independent variable) Goes on the Y axis (vertical) Should be on the right side of a data table.

Range

–Subtract the lowest data value from the highest data value.

–Do each variable separately.

30 - -40 = range of 70°

Scale–Spread the graph to use MOST of the available space.

–Determine a scale,(the numerical value for each square),that best fits the range of each variable.

10%

10%

Label Axes

• You need to tell everyone reading your graph what the graph means.

• Label each axis.• Be sure to include

units.

Plotting

• Plot each data value on the graph with a dot. You can put the data number by the dot, if it does not clutter your graph.

Drawing

–Draw a curve or a line that best fits the data points.

–Most graphs of experimental data are not drawn as "connect-the-dots".

Title• Your title should clearly tell what the

graph is about.

• If your graph has more than one set of data, provide a "key" to identify the different lines.

Interpolation

• Interpolate: predicting data between two measured points on the graph.

Extrapolation

• Extrapolate: extending the graph, along the same slope, above or below measured data.

Conclusion

• A conclusion statement is a statement that presents the findings of the experiment, what the data shows, and states if the hypothesis was correct (supported) or incorrect (negated).