Learn
Scientific Method in Everyday Life
Whether you realize it or not, you follow the scientific method everyday. Let's say you are baby–sitting one of your neighbor's children. The baby starts crying. Obviously, this is a problem. You probably form a hypothesis or guess about what might be the matter.
Since you have not fed the baby, you decide that the baby is most likely crying because she is hungry. If the baby is hungry, you predict, then she will stop crying if you feed her. You test this idea by giving the baby a bottle. The baby refuses the bottle and continues to cry. You conclude that the baby must not be hungry and that she is crying for another reason. What other hypotheses could you come up with? How could you test them?
The scientific method is not a process used only by stodgy scientists; you use it everyday of your life!
The scientific method is a process of many steps, and these steps are often repeated.
Watch the following video to learn more: PBS Learning Media: The Scientific Method.
While these steps of "question, research, hypothesis, experiment, data collection, and conclusion" in this exact order are taught as the scientific method, scientists do not always follow these procedures step-by-step each time.
- For example, a scientist may not make a hypothesis before months (or even years!) of gathering data or observations of a phenomenon (such as weather).
- Or, a scientist may perform an experiment and then realize they need to go back and modify the experiment and do it again before coming to a conclusion.
- Some experiments don't even really lead to true conclusions but rather lead to more questions and the need for more data.
Overall, the goal of understanding this process is to help you better “think like a scientist,” not necessarily to learn to follow specific steps in the correct order every time.
Hypothesis
Let's take a closer look at just exactly what hypotheses are and work a little on developing them. Your hypothesis is an informed guess based on your observations. A hypothesis is not a question. It is a statement of what you think is true, based on your research.
Some sample hypotheses include:
- “Washing hands in warm water kills more germs than washing hands in cold water.”
- “Cats sleep more than dogs.”
- “You can't distinguish between regular and diet soft drinks while wearing a blindfold.”
A hypothesis might be true or it might not be true. A hypothesis is tested in an experiment to determine whether it is true or false.
Experiments
Experiments distinguish scientific study from other areas of academics. Because an experiment provides the data for your conclusions, it must be carefully designed. Planning, conducting, and repeating experiments is an integral part of the scientific method. The procedure of an experiment is always very detailed, so that anyone can repeat the experiment and obtain the same results. The procedure is like a recipe; if you were explaining how to bake cookies, you don't just tell someone to mix together some flour and sugar. You explain exactly how much of each substance to add.
Most of the experiments we will talk about are controlled experiments. This means that controlled experiments have at least two groups:
- one or more experimental groups that receive the experimental treatment, and
- a control group that does not receive the treatment.
What is the purpose of the control group? It is compared and contrasted with the experimental group to see if the experimental treatment led to different results.
For example, you could conduct a controlled experiment on your fruit trees to see if adding compost will increase fruit production. You would add compost to half of your plants, which would be the experimental group, and grow the other half of your plants (the control group) without compost. You may think of the control group as the “normal” group.
In this experiment, the fruit trees receiving compost are the experimental group and the trees that do not receive the compost are the control group.
Variables
The different conditions or factors that affect an experiment's results are called variables. Light, temperature, water, type of soil, and soil acidity are all variables that affect a plant's growth.
The variable that the experimenter manipulates or changes during an experiment is called the independent variable.
For example, in an experiment examining the effects of air temperature on plant growth, we would have 3 groups of plants:
- a group in a room with the thermostat set to 60°F
- another group in another room set at 68°F (room temp.)
- a third group in a third room set at 76°F
The temperature would be the independent variable in this experiment because we decided which temperatures to use and we controlled the temperature by adjusting the thermostat.
The dependent variable is the factor that changes in response to the independent variable. Plant height is the dependent variable in our example because plant height changes depending on the temperature of the room.
In order to make sure that the independent variable--the factor that you are testing--is the only condition influencing the dependent variable, all other conditions are held constant, or the same. We would need to make sure that all of our plants were receiving the same amount of light and water and were planted in the same type of soil to guarantee that any differences we saw are related to the temperature. Are there any other conditions that should be held constant for our plants?
Example Experiment
A well-designed experiment displays all of the elements discussed so far in the lesson. Let's imagine you are completing an experiment to see if the colors of your clothes affects how hot you get when you're outside in the sun. You predict that black clothes will make you hotter than white clothes. To test your hypothesis, you find two friends - one is dressed in black jeans and a black long-sleeve t-shirt and another is dressed in white jeans and a long-sleeve t-shirt. You get them to stand outside in direct sunlight in 85° weather for 30 minutes. You take their external body temperature at the beginning of the experiment and again at the end (after the 30 minutes of sun exposure). Sure enough, the external temperature of the black clothes is higher than the white clothes -- so your hypothesis was correct!
Think about the following questions as related to this experiment.
- What is the independent variable in this experiment?
- What is the dependent variable?
- What are some constants in this experiment?
Now that you've thought about your responses, let's see if you're correct:
- What is the independent variable in this experiment?
- What is the dependent variable?
- What are some constants in your experiment?
There isn't really a control group in this experiment. Think of an idea for a good control group to help improve the design of this experiment!