Scientific Method – Experimental Design Controls and Variables

Scientific Experiments Follow Rules. An experimenter changes one factor and observes or measures what happens.

Observation vs. Inference Observation: Using one or more of the 5 senses to gather information Inference: Development of ideas based on observations Prediction: Use of knowledge to identify and explain observation or changes Warm Up: Take 5 minutes to look at the jar on your table. Write down ….. 4 observations 2 inferences

The Control Variable The experimenter makes a special effort to keep other factors constant so that they will not effect the outcome. Controls are NOT being tested Controls are used for COMPARISON

Other Variables The dependent variable is what the investigator measures (or counts or records). For example, you may want to study peanut growth. One possible dependent variable is the height of the peanut plants.

Other Variables The independent variable is what the investigator deliberately varies during the experiment.

Example of Controls & Variables An example, suppose you want to figure out the fastest route to walk home from school. You will try several different routes and time how long it takes you to get home by each one. Since you are only interested in finding a route that is fastest for you, you will do the walking yourself.

What are the Variables in Your Experiment? Varying the route is the independent variable The time it takes is the dependent variable Keeping the same walker throughout makes the walker a control variable.

One more thing… it is best to make several trials with each independent variable.

Data = Information gained from observations Quantitative Data: numerical data (measurements of time, temperature, length, mass, area, etc.) Grass experiment = Area of healthy grass vs. area of dead grass Qualitative Data: descriptions of what our senses detect Grass experiment = More healthy grass vs. less dead grass