Students will perform investigations to describe a phenomenon or to test a prediction or model for how the world works. For example, scientific experiments may be performed to observe different outcomes when test subjects encounter different conditions. Engineering investigations might be performed to find out how to fix or improve the technological system or to compare different solutions to see which best solves a problem.
Whether students are doing science or engineering, it is always important for them to state the goal of an investigation, predict outcomes, and plan a course of action that will produce data that may be used as evidence to support their conclusions. These data can be quantitative (numerical) or qualitative (descriptive observations), but should be consistently collected and measured.
Thinking about variables
Scientists and engineers use investigations to search for cause-and-effect, explore relationships in nature or test differences in design prototypes. They design an experiment so that changes to one item causes something else to vary in a particular way.
The changing factors in an experiment are called “variables.”
Independent and dependent variables
A variable is any condition that can change. An experiment usually has two types of variables: independent or dependent.
Independent variables are conditions that can be changed by the scientist. To insure what is called a “fair test,” a good experiment has only one independent variable that they change. All other independent variables should be held constant. As the scientist changes the independent variable, they observe what happens to the dependent variable.
The scientist measures the response of the dependent variable(s) to see how it is affected by the change made to the independent variable.
For example, if you are growing corn and you want to measure the effect of different fertilizers, you could observe how different fertilizers (independent variable) affect the height and number of corn kernels produced (dependent variables). The amount of water, type of soil, temperature, and hours of sunlight should remain the same for all test subjects in order for this experiment to be a fair test.
Experiments must have a basis of comparison. This is known as the “control.” In the corn fertilizer experiment, the scientist should also have a group of plants (at least 5) that receive no fertilizer, but are grown under the same conditions as the fertilized plants.
In their lab notebook, the student should specify their “treatment groups” (or “experimental groups” where the independent variable is changed) and “control group” (where no variables are changed, creating a baseline).
Students must be able to measure the values for each variable. Weight or mass, temperature, and distance are examples of variables that are very easy to measure. In contrast, if an investigation had a highly subjective variable such as “love,” the scientist would have a hard time determining a unit of measurement for that variable.
A well-planned experiment will allow the student to compare the control group with the treatment groups. This will help insure that any observed changes in the dependent variable are in fact correlated with the independent variable.
Some conditions, such as the weather, cannot be controlled by the student. These conditions may still have an affect on the results of their investigations and should be recorded. These can be identified as “limitations” in their discussion section. Unforeseen and unexpected situations may arise and are not mistakes. It is considered a positive thing when a scientist can identify them and use that information to plan differently in the future.
For example, if you are running trials varying the type of material used to build a paper airplane to determine which prototype will fly the farthest, strong wind would be an uncontrollable condition that may impact on your results.
Developing a plan
When designing an investigative procedure, the student should determine how they will change their independent variable and how they will measure the impact that this change has on the dependent variable.
When planning investigations, students should also consider:
- Is the investigation safe to perform?
- Do they have all the materials and equipment needed, or will they be able to obtain them quickly and at a low cost?
- Do they have enough time to do their investigation before any deadlines? (It is important to calendar out their project.)
- What is the ideal sample size for their experiment? (Larger sample sizes yield more reliable results.)
- Does the project meet all the rules and requirements for any science and engineering fairs or competitions to which they may be submitting their final project?
After having thoroughly researched their question, students should have some predictions regarding the answer to their question or solution to their problem.
Predictions or hypotheses should include what the students will do, what they think will happen as a result, and their reasoning (based on scientific rationale).
Ex: “If ___[I do this]___, then ____[this]____ will happen because____________.”
Approval before experiment
Some science fair projects that involve human subjects, vertebrate animals (animals with a backbone) or animal tissue, pathogenic agents, DNA or controlled or hazardous substances, need Scientific Review Committee (SRC) approval BEFORE they start experimentation.
Informed consent for human subjects
Projects that involve human subjects, including surveys, product testing, exercise, or observations, may require informed consent forms prior to conducting research.