Variables in a Controlled Experiment How to conduct a valid experiment

A Good Experiment Tests one variable at a time. If more than one thing is tested at a time, it won’t be clear which variable caused the end result. Must be fair and unbiased. This means that the experimenter must not allow his or her opinions to influence the experiment. Does not allow any outside factors to affect the outcome of the experiment. Is valid. The experimental procedure must test your hypothesis to see if it is correct. If it does not test your hypothesis the data will make no sense. Has repeated trials. Repeating the trials in the experiment will reduce the effect of mistakes and give a more accurate conclusion.

Variable A variable is anything in an experiment that can change or vary. Three main types: Independent Variable: what you change Dependent Variable: what you measure Controlled Variable (controls): what is kept the same and not changed (to keep it “fair”)

Example Experiment Students of different ages were given the same jigsaw puzzle to put together. They were timed to see how long it took it finish the puzzle. What are the variables in this experiment?

What are the variables? Students of different ages were given the same jigsaw puzzle to put together. They were timed to see how long it took it finish the puzzle. Independent Variable: Dependent Variable: Control Variable: Age of the students Time taken to finish puzzle Same puzzle done by all, to keep it “fair”

Another Example Experiment The temperature of water was measured at different depths of a pond. What are the variables in this experiment?

What are the variables? The temperature of water was measured at different depths of a pond. Independent Variable: Dependent Variable: Control Variable: How deep the water is Temperature of water Same pond Same thermometer

Activity: Paper Airplanes! Purpose: Which design of paper airplane will fly the farthest? Hypothesis: If I make an airplane with these features _________________ , then it will fly farther, because __________________________ .

Variables: Independent: What can we change in the design? size, kind of materials for plane, using tape, using paper clips, kind of wings, kind of tail Dependent: what will we measure? How far the plane flies Controls: What must we keep the same to be “fair”? Use only paper for body of airplane (not cardboard, wood or metal bodies).

Now make your plane! Use only paper for the body of the plane (scrap paper on the demo table). You may use paper clips or tape. No other materials! Be ready to test your plane near the end of class. Get into a group of 2 or 3 people.

Last One Students modified paper airplanes by cutting pieces off, adding tape, or adding paper clips to increase the distance thrown. What are the variables in this experiment?

What are the variables? Students modified paper airplanes by cutting pieces off, adding tape, or adding paper clips to increase the distance thrown. Independent Variable: Dependent Variable: Control Variable: Weight, center of gravity, or air resistance (BUT ONLY ONE!) Distance thrown Same plane design Same paper Same way thrown