Designing a Controlled Experiment
Step 1: Defining the Problem
Every scientific investigation begins with the question that the scientist wants to answer. The questions addressed by scientific inquiry are based on observations or on information gained through previous research, or on a combination of both. Just because a question can be answered doesn’t mean that it can be answered scientifically.
Step 2: Defining the Dependent and Independent Variable
Dependent Variable (DV) | Variable the experimenter measures, after making changes to the IV that are assumed to affect the DV. | Independent Variable (IV) | Variable the experimenter manipulates (i.e. changes) – assumed to have a direct effect on the dependent …show more content…
(b) Light absorption by a pigment is measured for red, blue, green, and yellow light. Dependent variable: light absorption Independent variable: pigment
Step 3: Writing the Hypothesis (if necessary)
A hypothesis is simply a statement of the scientist’s educated guess at the answer to the question. A hypothesis is usable only if the question can be answered “no”. If it can be answered “no”, then the hypothesis can be proven false. The nature of science is such that we can prove a hypothesis false by presenting evidence from an investigation that does not support the hypothesis. But we cannot prove a hypothesis true. We can only support the hypothesis with evidence from this particular investigation.
For example: If the temperature of the solution increases, then the reaction will happen faster.
Practice: Create a hypothesis statement for the following testable questions. Remember to include an IV and a DV. 1. What is the effect of temperature on the speed of sound in air?
Hypothesis: If the temperature increases, the speed of sound in air increases.
2. How does caffeine affect a person’s heart rate?
Hypothesis: If the person takes high concentration of caffeine, then the heart rate will increase.
Step 4: Identifying the Standardized (control) Variables
Standardized variables are factors