Scientific method virtual lab middle school

Scientific Method: Post-Lab LEARNING GOALS By the end of this unit, you should be able to do the following: 1. Describe the steps of the Scientific Method. 2. Define dependent and independent variables. 3. Write a testable hypothesis. 4. Describe the meaning and purpose of experimental controls. 5. Gather data from an experiment and analyze the results. 6. Determine whether data support or reject the experimental hypothesis. Chances are you have studied the steps of the scientific method every year of grade school and are also studying it now in lecture. Rather than reviewing that material again, we will focus here on applying the practical elements of the scientific method to real experiments. Our three main topics will be variables, control experiments, and the hypothesis. Make an Observation Figure 1: Steps of the Scientific Method (Michael Fullerton Creative Commons 4.0) VARIABLES When designing an experiment, there are many different options of how to do things. How much water you pour in the cup, how long you wait, what you measure, how you measure it, all of these are variables. The three types of variable are independent, dependent, and control. The independent variable is the condition you are testing. For example, if you are testing which brand of dog food dogs like best, the independent variable is the different brands of dog food. If you are testing which brand of fertilizer works best, the independent variable is the different types of fertilizer. Another way to recognize this variable is that this is the condition you are "changing on purpose" between each experiment. The independent variable is also called the experimental variable. The dependent variable is the data you are taking on your experiment. This is the information you will use to make your conclusions later. If you are testing which brand of dog food dogs like best, the dependent variable might be how much of each brand the dogs eat, or possibly which of the brands the dog eats first. If you are testing which brand of fertilizer works best, the dependent variable might be how tall each plant grows or how much fruit they produce. Another way to recognize this variable is that this is the value that you think will change based on the changes you make to the independent variable. You think that this value "depends" on the condition you are testing. The control variables are elements of the experiment that you take deliberate action to keep the same. Back to our dog food test, putting the same amount of food in each bowl is a control variable. In the plant experiment, giving the plants the same amount of water is an important control variable. Things that stay the same without you taking deliberate action do not count as control variables. Essentially, if you don't identify them ahead of time, they are not control variables. Also, control variables are usually things you think might alter the outcome of the experiment. You can't control everything, so you have to focus on those things that you think are actually important. Most of the errors made when designing or reporting on experiments involve the three types of variables. Sometimes a second independent variable sneaks into the experiment. This is sometimes something that should have been a control variable, but the experimenter didn't pay attention to it. In the plant fertilizer experiment, if some fertilizers are liquid and others are solid, the plants receiving the liquid fertilizer are also receiving more water. This is because the fertilizer is dissolved in water. The total amount of water must be adjusted for these plants so that you aren't accidentally making water amount an independent variable. Another common error is failing to plan out the dependent variable. In our dog food experiment, failing to define what "better" means ahead of time can cause problems. When putting out three types of dog food at the same time, is better defined by which food the dog eats first or which one the dog eats the most of? One final common cause of error is waiting until the end of an experiment to name the control variables, then choosing things which were coincidentally the same. In our plant fertilizer experiment, you shouldn't list "room temperature" as a control variable. True, the plants were all grown at the same temperature because they were in the same room, but you didn't take deliberate action to make this so. Experiment Note - For every experiment we do in class, you should identify all three types of variables before you begin the experiment. CONTROL EXPERIMENTS Control experiments are used to set the baseline for your experiments and also to make sure your measurement for the dependent variable works. The negative control lets you know the value of the independent variable without treatment. In our plant fertilizer experiment, a plant with no fertilizer serves as the negative control. This lets you know how much a plant should grow on its own. The negative control is also sometimes called the control group. When testing the effectiveness of any treatment, the group that does not receive the treatment is called the control group. A positive control lets you know that your basic experiment conditions are valid. In the plant experiment, the plant without fertilizer also serves as a positive control.