Scientific Method

Scientific Method• Science is the use of evidence to

develop testable explanations and predictions of natural phenomena.

• The scientific method is a systematic approach used in scientific study.

Scientific Method

Steps in the scientific method include:1. observation: the act of gathering

information2. hypothesis: a testable explanation or

prediction3. experiment: set of controlled

observations that test the hypothesis. 4. conclusion: judgment on the

information obtained

Scientific Method

Observation

Hypothesis

Experiment

Conclusion

A. Observations

• Observations can be quantitative or qualitative

• A qualitative observation does not include a numerical value.

• A quantitative observation includes a numerical value.

Measurement

• A measurement consists of two things: a quantitative observation (magnitude) and a unit

Examples

0.7 mm

Magnitude(quantity)

unit

120 lbs

Magnitude(quantity)

unit

The paragraph below was a summary of a chemistry experiment done a few years ago. Write down 5 qualitative observations and 5 quantitative observations:

Monica measured 2.20 grams of copper chloride dihydrate. The copper chloride dihydrate was

bright green and looked like the pop rocks candy. Once the copper chloride dihydrate was

dissolved in 25 mL of water, it turned into an aqua blue solution. The temperature of the

solution was 22°C. Next, 0.45 g of aluminum foil was loosely balled up and added to the solution. Bubbles immediately formed and the aluminum started to turn dark red. Condensation formed along the sides of the beaker, and the overall

solution turned dark green, then grey. The final temperature of the solution was 42°C.

Scientific Method

Observation

Hypothesis

Experiment

Conclusion

B. Hypothesis• Hypotheses are tentative and testable

statements that are capable of being supported or not supported by observational evidence.

• Hypotheses of durable explanatory power which have been tested over a wide variety of conditions are incorporated into theories

• Related to the data provided• Hypotheses that involve testing the

emotions of animals are not valid.

Clouds are more beautiful on winter days than on summer days. This statement is a poor hypothesis because it is not —

A a questionB testableC observableD a comparison

Students placed equal amounts of bread mold on 12 identical agar plates containing the same amounts and types of nutrients. Four plates were kept at 0°C, four were kept at 45°C, and four were kept at 22°C (room temperature). The plates were examined after five days. Which of the following was probably the hypothesis for this experiment?

F The growth of bread mold increases as temperature increases.

G The type of nutrient causes bread mold to grow faster at higher temperatures.

H The size of the plates determines the temperature of bread mold.

J The temperature of bread mold is determined by the mold’s growth.

Hypotheses vs Theories

• Scientific theories are based on natural and physical phenomena and are capable of being tested by multiple independent researchers. Unlike hypotheses, scientific theories are well-established and highly-reliable explanations, but may be subject to change as new areas of science and new technologies are developed.

Theories you may have heard of:• Theory of evolution• Big Bang theory

Theories vs Laws

• A theory is an explanation that has been supported by many, many experiments. Note, theories are constantly evolving and grow stronger as we learn more. Theories provide an explanation for a wide range of observations. A good theory can be used to make predictions.

Theories vs Laws

• A (scientific) law is an observation only of natural phenomena. It offers no explanation as to why it happens.– Ex: Gravity is a law. We have no

concrete explanation for it. Plate tectonics is a theory. It explains and predicts volcanoes and earthquakes

Scientific Method

Observation

Hypothesis

Experiment

Conclusion

Important parts of an experiment include:• 1 variable is being tested (independent

variable)• Dependent variable is being measured• Many controlled variables• 1 experimental control (for comparison)• Be precise by using precise equipment &

the same equipment each time• Do multiple trials!!! • Average your results from the multiple

trials• Make a note of any outlying data or

experimental errors

In experiments, a benefit of larger sample sizes would be more —

A variablesB representative dataC time per groupD control groups

An engineer has created a new engine for race cars. It is necessary to know which fuel mixture will allow the engine to run at its peak performance. Which experimental design is best for this investigation?F Use one fuel mixture on the engine and measure

its performanceG Use one fuel mixture on many types of engines

and measure their performanceH Use various fuel mixtures on the engine and

measure its performanceJ Use various fuel mixtures on many types of

engines and measure their performance

Variables

Experiments will consist of variables (a quantity or condition that can have more than one value.)

Experimental Control

Experimental Control: An experimental control is something that is not manipulated and is being used for comparison.)

Sample Problem

3 Types of Variables

• Independent variable: the one that you deliberately change (manipulative)

• Dependent variable: the one that you measure (responding)

• Controlled variables: a factor that is not allowed to change during the experiment

Variables

IndependentDependent

Controlled

manipulative Being

Changed

Being measure

dDepends on the Ind. Var.

Doesn’t Change Several per

experiment

On X axisOn Y axis

PracticeStudents placed equal amounts of

bread mold on 12 identical agar plates containing the same amounts and types of nutrients. Four plates were kept at 0°C, four were kept at 45°C, and four were kept at 22°C (room temperature).

Determine the following:Independent Variable = Dependent Variable =Controlled Variables =

Experimental Control =

Temperature of the samples

Amount of bread mold

Hypothesis:

The growth of bread mold increases as temperature increases.

Types of plates, amount of nutrients, type of nutrients, etc.Samples at room

temperature

Recording your data on a data table

• Include a title• Include units• Independent variables can be filled in

before the experiment• Measured/Dependent variables are filled in

as you complete the experiment

title

units

Independent Var. Dependent Var.

Graphing your results

• Use a pie/circle graph for percentages (parts of a whole)

CoconutCream 3%

Scientific Method

Observation

Hypothesis

Experiment

Conclusion

D. Conclusions• A summary of the experiment that

reflects the data you collected• Graph your data & determine any

trends• “DRY MIX” = dependent or

responding variable on the Y-axis & manipulative or independent variable on the X-axis

DRY MIXDependent or Responding on Y

Manipulative or Independent on X

Y

XIndependent Variable

Dependent

Vari

able

Determine the Dependent &

Independent Variables

Independent Variable

Dependent

Vari

ab

le

ExperimentAmount of Studying vs Test

Grades

• What is my independent variable?• What is my dependent variable?• What are my controlled variables?

• How would I label my axis in a graph?

Studying Vs Test Grades

Independent Variable

Dependent

Vari

ab

le

Tes

t G

rade

s

Amount of Studying

In this experiment, what needs to stay the same?

(what are some controlled variables)

Graphing your results

• Graphing your results– Use a pie/circle graph for percentages– Use a bar graph when you are counting – Use a line graph when you are

comparing points– Use a scatter plot with a best fit line

when you are looking for a trend.

D. Conclusions

o Two quantities are directly proportional if dividing one by the other gives a constant value. If graphed, it would produce a straight line. As one variable increases, the other variable increases.

EX: moles and Liters in molarityMolarity= moles/Liters

Is your data directly proportional or inversely proportional?

D. Conclusions

o Two quantities are inversely proportional to each other if their product is constant. A graph of an inverse proportion would produce a curve. As one variable increases, the other variable decreases. EX: mass and acceleration in Newton’s second law F=ma

Is your data directly proportional or inversely proportional?

Conclusion vs Inference

• A conclusion is simply a statement based only on experimental facts

• A inference which makes a statement beyond the facts.

Conclusion vs Inference

Ex: You heat a liquid substance and a gas is produced.

Conclusion: When liquid A was heated, a gas was produced.

Inferences: A gas was produced because liquid A was heated.

Conclusion