Inver Hills Community College Scientific Method & Experimental Design Paper

INTRODUCTION:

Scientists study the world around them through a series of steps known as the scientific method.The series of steps are as follows:

• Observation
• Question
• Hypothesis
• Experiment
• Analysis
• Conclusion
• Observation—your car won’t start
• Question—why won’t it start?
• Hypothesis—dead battery, ignition problem, out of gas (you actually had 3 hypotheses in this case)
• Experiment—turn on radio, look for ignition spark, check gas gauge
• Analysis—radio works, ignition spark present, gas gauge reads “E”
• Conclusion—your car is out of gas

Please note that different scientists and different textbooks may list this series of steps slightly differently than listed above.

The scientific method is a way of finding answers to questions.This is something that everyone does every day!For example, let’s say that after class you head out to the parking lot to go home and discover that your car won’t start.One of the first things you likely do is wonder about why your car won’t start.Perhaps your battery is dead.Or there’s an ignition problem.Or you’re out of gas.Well, if you want to get home, you need to figure out which of these is the problem.So you try turning on your radio, check for a spark at the plug, or look at your gas gauge.You discover that your radio still works, there’s an ignition spark, but your gas gauge reads “E”.Now you know that you’ve run out of gas and need to put some in your car in order to get home.You’ve solved the problem.And you did it using the scientific method (even though you likely didn’t realize it)!

Let’s work our way through the steps of the scientific method using another example.

Step 1:Observation(s). I’ve noticed that after it rains in the summer, my lawn seems to grow a bit faster.

Step 2:Question(s).What factors are affecting the growth of my lawn?Specifically, does the amount of water affect the growth of my lawn?Note that my specific question states my variables (go back to the previous lab if you need to review).Take a moment to underline the variables in my question, and determine which is the independent variable and which is the dependent variable.

“Does the amount of water affect the growth of my lawn?”

Independent variable:

Dependent variable:

Step 3:Hypothesis (hypotheses).A hypothesis is sometimes described as an educated guess.It is your prediction as to what the answer to your question will be.Hypotheses are based upon previous knowledge and observations.There are multiple ways to write hypotheses.For this lab, we are going to write hypotheses as “if…., then….” statements, which will help ensure that our hypotheses include all the necessary information.The “if” part of the statement identifies the relationship you are studying.That is, it states your independent and dependent variables.For example, “If the amount of water is related to the growth of my lawn…”.The “then” part of the statement is where you make your prediction as to what the relationship will be.For example, “then an increase in the amount of water will increase the growth of my lawn.”Note that my prediction is very specific as to exactly what I think the relationship will be.Don’t be vague in your hypotheses!Let’s practice.For each of the following questions, write a hypothesis.

“Does chocolate affect the number of pimples acquired?”

“Does temperature affect the growth of bacteria?

Step 4: Experiment(s).The purpose of experiments is to test our hypotheses.To accurately test our hypotheses, we must think carefully about our experimental design before we start collecting our data.Some factors to consider include:

• control groups
• constants (controlled variables)
• group size
• quantitative vs. qualitative data
• repetition

Let’s say that I test my hypothesis (“if the amount of water is related to the growth of my lawn, then an increase in the amount of water will increase the growth of my lawn”) by simply watering my lawn with a sprinkler every day for a month, and after the month I conclude that my lawn grew faster.However, what if my neighbor’s lawn grew just as fast even without extra water?I need to include a control group to my experimental design.A control group is a group that is not manipulated during the experiment and serves as a basis for comparison.The control group(s) is compared to the experimental group(s) which is manipulated during the experiment.In our example, my lawn that is getting extra water through the use of a sprinkler is the experimental group.A neighbor’s lawn that is only getting water from rainfall is the control group.

We also need to consider other variables that might affect lawn growth.What if my lawn grew faster not because of extra water, but because it got more sunlight?In order to be able to draw a valid conclusion, we need to eliminate these other factors.These other factors need to remain the same throughout the experiment.These factors are referred as constants or controlled variables.

We already said that sunlight needs to be a constant (controlled variable).What other factors can you think of that should be kept constant in order to test our hypothesis?List at least 3.

a.

b.

c.

There are a few other things we can do to increase the validity of our experiment.We should have a large group size.Group size refers to how many individuals are in our control group(s) and experimental group(s).By having large group size, we are able to reduce the impact of variations we forgot or are unable to keep constant.So instead of comparing just my lawn to my neighbor’s lawn, I should compare several watered lawns to several unwatered lawns.We should measure quantitatively, not qualitatively.Quantitative data refers to numbers, whereas qualitative data consists of non-numerical data.Quantitative data is preferred as there is less bias with this type of data.Bias refers to a tendency or opinion, often based on preconceived ideas.Therefore we should measure the growth of our lawns with a ruler, as opposed to just saying that it looks longer (or greener).Please note that the metric system is used in science, so you should use the metric system whenever possible in this lab. Finally, we should repeat our experiment.Repetition (also called replication) helps us ensure that our results are true.

Step 5: Analysis (analyses).Once data has been collected, it needs to be analyzed.This can involve the use of statistics and generation of tables and graphs.Please refer to the “Working with Data” lab for more information.

Step 6: Conclusion(s).Finally, we draw a conclusion about our hypotheses.Based on our data, we can either “accept” or “reject” our hypotheses.We can never “prove” a hypothesis, as other experiments and data may disprove it later.It is perfectly okay to reject a hypothesis.A rejected hypothesis is typically re-evaluated, and a revised hypothesis is tested.

ACTIVITY: Now that we’ve gone over the scientific method, it’s time for you to practice it in small groups.We’ll work with something we’re already familiar with…paper airplanes!

Step 1: Observation

I’ve noticed that the design of paper airplanes affects the distance that they fly (observation).

Step 2 : Questions

What are some variables in the design of paper airplanes that might affect the distance flown?List at least 3.

a.

b

c.

These are independent variables.They cause a response.The dependent variable is the response.What is your dependent variable?

Step 3: Hypothesis

Select one of your independent variables to test.Write a hypothesis about the effect of your chosen variable on the dependent variable.Remember to use the if….then… format, and be specific in your prediction!

Step 4:Experiment

What is your control group?

What is your experimental group?

What are your constants (list at least 3)?

a.

b.

c.

Write out your experiment methods.In addition to a control group and constants, be sure to consider group size, type of data to collect, and repetition. Provide enough detail in your methods that I could replicate your test!

Step 5: Analysis

Provide both a table (raw data) and a graph of your results.Review the “Working with Data” lab if you’re not sure what type of graph to make.Also consider whether you might need to do some simple statistical analyses in order to present your data as simply as possible.Be sure to provide titles, label axes, units, etc.This should be a stand-alone document.I should be able to look at your results and understand your experiment without reading anything else in this document!Don’t forget to attach both your table and graph to your lab.

Step 6: Conclusion

Do you accept or reject your hypothesis?Why?

Why do you think you got the results that you did?Be detailed!Don’t just tell me (for example) that plane A flew further because it weighed more.Give me a reason as to why and how weight made a difference.