Experimental Design & the Scientific Method

Experimental Design &the Scientific Method Physical Science 8 2013-2014

Variable The condition or factor that CHANGES in an experiment so the effects can be observed.

Dependent Variable (DV) A variable whose value DEPENDS on the value of another variable. To identify, ask:What is actually being measured in the experiment? When graphing, usually goes on Y axis.

Independent Variable (IV) A variable whose value does not depend on the value of another variable. To identify, ask:What is being changed to see an outcome in the experiment? When graphing, usually goes on X axis.

Control Group/Constants A condition or factor that is kept the same throughout an experiment. To identify, ask:Which group is receiving no “treatment”? A proper experiment must have a control.

Experimental Group A condition or factor that is changed or tested in an experiment. To identify, ask:What is being changed to see an outcome in the experiment? A proper experiment will only change ONE thing at a time!

Qualitative Data • Deals with descriptions. • Data can be observed but not measured. • Colors, textures, smells, tastes, appearance, beauty, etc. • Qualitative → Quality

Quantitative Data • Deals with numbers. • Data which can be measured. • Length, height, area, volume, weight, speed, time, temperature, humidity, sound levels, cost, members, ages, etc. • Quantitative → Quantity

The Scientific Method Definition: An organized way to solve a problem.

Step #1 State the Problem Which means: What is the effect of _________ on _________?

Step #2 Gather information Which means: research (books, on the internet, journals, etc)  observations (using your 5 senses!)

Step #3 Form a Hypothesis Which means:  Make an educated guess based on your research! must be written in “If this…. then that” format  must be measurable

Step #4 Perform Experiment Which means:  step by step procedure  identify control and experimental group  list materials needed

Step #5 Record and Analyze Data Which means:  use data table, graphs and charts to organize  does the data make sense?

Step #6 Reach a Conclusion Which means: Always state whether your hypothesis was correct.  Explain why or why not, sources of error, and what happened.

An example A student wonders if it possible to float a cork in the middle of a glass of water without touching it. He looks up the density of a cork and of water on the internet. He finds out that water has a higher density than the cork. He also looks in his science book to see if the experiment has been done before, but it hasn’t. From the information he gathers, he does think that a cork will float in the center of a glass of water. He puts the materials for his experiment (a plastic cup, a cork, a spoon, and water) together. He finds a flat surface and fills the cup with water and drops the cork in. He writes down on a sheet of paper his results. The cork does float in the water, but it goes to the side of the cup. He then blows on the cork and again, it goes only temporarily to the middle of the cup, but then goes back to the side. He writes that down. Finally, he adds one spoonful of water at a time until the water is almost coming over the top, but not spilling over. The cork floats in the middle and stays there! The student felt excited by his results.

Cork Example • What is the problem? • What information did the student gather and where did he gather it from? • What was his hypothesis? • What did the student do in his experiment? (list the steps) • What would his data table look like? • What was his conclusion?

Experimental Design & the Scientific Method