• anonymous
Experimental Design: From the work you have done this semester, choose a topic and design an experiment you would be able to perform. In your design (1) state your hypothesis, (2) identify your dependent and (3) independent variables, (4) your control conditions and (5) describe your experimental procedure.
  • Stacey Warren - Expert
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  • chestercat
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  • Cicilybailey14
Hypothesis The most common way a hypothesis is used in scientific research is as a tentative, testable, and falsifiable statement that explains some observed phenomenon in nature. We more specifically call this kind of statement an explanatory hypothesis. However, a hypothesis can also be a statement that describes an observed pattern in nature. In this case we call the statement a generalizing hypothesis. The hypothesis statement can be followed by the specific, measurable prediction you can make if the hypothesis is valid. Thus, we can think of the hypothesis in science as an explanation or generalization on trial. A prediction in science is a prophecy, a specific and measurable event that is likely to happen in the future as the result of an experiment if the hypothesis is valid. Teaching the Hypothesis Incorrectly Many teachers and even many textbooks teach the hypothesis in a way that makes it no different from a prediction. They teach students to write “If – then” statements for their hypotheses. This approach results in the incorrect form: If I do X, then Y will happen. There is no hypothesis here. This is simply a method (if I do X) followed by a prediction (then Y will happen). Some teachers and textbooks add “…because…” at the end of the “If…, then…” statement. The because statement is often close to the hypothesis that is being tested, but it still does not carefully delineate the hypothesis from the prediction. Indeed, even professional scientists can make mistakes. Variables There are three different kinds of variables you should define in your lab writeup: the independent variable, the dependent variable, and controlled variables. Controlled Variables (CV) Controlled variables are factors which could affect the dependent variable but are kept constant throughout the experiment. Several controlled variables should be listed (usually four is a good amount). For example, if the experiment is testing to see how fast a parachute falls with different mass, a constant variable could be "Height at which parachute is dropped (in meters)". Only four need to be listed to receive full credit for this section. Independent Variable (IV) This is the variable that is changed to examine its effect on the dependent variable. There should only be one IV, which should be listed with units. The IV must be operationally defined (in terms of the experiment) and empirically defined (in general for future variations of the experiment), and a minimum of 3 different levels must be listed excluding the control level. Dependent Variable (DV) The dependent variable is what is affected by the independent variable. It should be defined in units. Using the same previously given experiment, this would be "Time it takes for parachute to fall (in seconds)." The dependent variable must be operationally and empirically defined, and levels are unnecessary because that is what will be determined through the experiment. Control or "Standard of Comparison" A rationale for the control should be included. The SOC is basically the object that is the "normal" one, the one that hasn't been changed at all. For example, if you were doing an experiment on how long a can spins v.s. how many holes it has in it, the SOC would be the can with no holes in it. Changing your IV to zero, or using the highest or lowest possible numeric value makes a good SOC. Materials When you list out your materials, be sure to be extremely specific. List the quantity of the materials to be used. It is a good idea to write down brand names or companies next to the material. After all, different companies make different versions of the same thing. When you list your independent variable (say you are testing using rocks with three different weights), write "Rocks (light, medium, heavy). If you aren't sure whether or not to list the materials you used to measure (meter sticks, time pieces, etc.), ask the event supervisor. Some competitions want you to list the measuring devices, while others may take off points for it. Do not list the materials on the front cover of the test; it is unlikely that you will use all of them, and you will get points off for listing unused materials. Procedure List the steps in your experiment clearly. Be sure to include labeled diagrams of how your experiment was performed. Three diagrams is typically sufficient, but more may be needed if an experimental apparatus needs to be constructed. To cut time, "Repeat steps X to Y" can be used, but make sure it makes sense. You can check yourself by thinking that if you could show any random person the procedure, would they be able to follow it clearly? Always have three trials for each step. Without this, a single data point may be an outlier—or it may be a real data point and you would never know. Remember to be specific all the time. The last thing on every procedure list should be "Clean up your workspace"- and be sure to do so!
  • Cicilybailey14

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