1.1: The Process of Science

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Skills to Develop

Explain the necessity for experimentation
In an experiment, identify the independent, dependent, and controlled variables.

Introduction

Socrates (469 B.C. - 399 B.C.), Plato (427 B.C. - 347 B.C.), and Aristotle (384 B.C. - 322 B.C.) are among the most famous of the Greek philosophers. Plato was a student of Socrates, and Aristotle was a student of Plato. These three were probably the greatest thinkers of their time. Aristotle's views on physical science profoundly shaped medieval scholarship, and his influence extended into the Renaissance (14\(^\text{th}\) century - 16\(^\text{th}\) century). Aristotle's opinions were the authority on nature until well into the 1300's. Unfortunately, many of Aristotle's opinions were wrong. It is not intended here to denigrate Aristotle's intelligence; he was without a doubt a brilliant man. It was simply that he was using a method for determining the nature of the physical world that is inadequate for that task. The philosopher's method was logical thinking, not making observations on the natural world. Let's consider two of Aristotle's opinions as examples.

In Aristotle's opinion, men were bigger and stronger than women; therefore, it was logical to him that men would have more teeth than women. Thus, Aristotle concluded it was a true fact that men had more teeth than women. Apparently, it never entered his mind to actually look into the mouths of both genders and count their teeth. Had he done so, he would have found out that men and women have exactly the same number of teeth.

In terms of physical science, Aristotle thought about dropping two balls of exactly the same size and shape but of different masses to see which one would strike the ground first. In his mind, it was clear that the heavier ball would fall faster than the lighter one and he concluded that this was a law of nature. Once again, he did not consider doing an experiment to see which ball fell faster. It was logical to him, and in fact, it still seems logical. If someone told you that the heavier ball would fall faster, you would have no reason to disbelieve it. In fact, it is not true and the best way to prove this is to try it.

Eighteen centuries later, Galileo decided to actually get two balls of different masses, but with the same size and shape, and drop them off a building (Legend says the Leaning Tower of Pisa), and actually see which one hit the ground first. When Galileo actually did the experiment, he discovered, by observance, that the two balls hit the ground at exactly the same time. . . Aristotle's opinion was, once again, wrong.

Scientific Methods of Problem Solving

In the 16\(^\text{th}\) and 17\(^\text{th}\) centuries, innovative thinkers were developing a new way to discover the nature of the world around them. They were developing a method that relied upon making observations of phenomena and insisting that their explanations of the nature of the phenomena corresponded to the observations they made.

The scientific method is a method of investigation involving experimentation and observation to acquire new knowledge, solve problems, and answer questions. Scientists frequently list the scientific method as a series of steps. Other scientists oppose this listing of steps because not all steps occur in every case, and sometimes the steps are out of order. The scientific method is listed in a series of steps here because it makes it easier to study. You should remember that not all steps occur in every case, nor do they always occur in order.

The Steps in the Scientific Method

Step 1: Identify the problem or phenomenon that needs explaining. This is sometimes referred to as "defining the problem."
Step 2: Gather and organize data on the problem. This step is also known as "making observations."
Step 3: Suggest a possible solution or explanation. A suggested solution is called a hypothesis.
Step 4: Test the hypothesis by making new observations.
Step 5: If the new observations support the hypothesis, you accept the hypothesis for further testing. If the new observations do not agree with your hypothesis, add the new observations to your observation list and return to Step 3.

Experimentation

Experimentation is the primary way through which science gathers evidence for ideas. It is more successful for us to cause something to happen at a time and place of our choosing. When we arrange for the phenomenon to occur at our convenience, we can have all our measuring instruments present and handy to help us make observations, and we can control other variables. Experimentation involves causing a phenomenon to occur when and where we want it and under the conditions we want. An experiment is a controlled method of testing an idea or to find patterns. When scientists conduct experiments, they are usually seeking new information or trying to verify someone else's data.

Experimentation involves changing and looking at many variables. The independent variable is the part of the experiments that is being changed or manipulated. There can only be one independent variable in any experiment. Consider, for example, that you were trying to determine the best fertilizer for your plants. It would be important for you to grow your plants with everything else about how they are grown being the same except for the fertilizer you were using. You would be changing the type of fertilizer you gave the plants and this would be the independent variable. If you also changed how much water the plants received, the type of plants you were growing, and some of the plants were grown inside and others outside, you could not determine whether or not it was actually the fertilizer that caused the plants to grow better or if it was something else you had changed. This is why it is important that there is only one independent variable.

The dependent variable is what is observed or measured as a result of what happened when the independent variable was changed. In the plant experiment described above, you might measure the height of the plant and record their appearance and color. These would be the dependent variables. The dependent variable is also sometimes called the resultant variable.

Controlled variables are conditions of the experiment that are kept the same for various trials of the experiment. Once again, if we were testing how fertilizer affected how well our plants grew, we would want everything else about how the plants are grown to be kept the same. We would need to use the same type of plant (maybe green beans), give them the same amount of water, plant them in the same location (all outside in the garden), give them all the same pesticide treatment, etc. These would be controlled variables.

Suppose a scientist, while walking along the beach on a very cold day following a rainstorm, observed two pools of water in bowl shaped rocks near each other. One of the pools was partially covered with ice, while the other pool had no ice on it. The unfrozen pool seemed to be formed from seawater splashing up on the rock from the surf, but the other pool was too high for seawater to splash in, so it was more likely to have been formed from rainwater.

The scientist wondered why one pool was partially frozen and not the other, since both pools were at the same temperature. By tasting the water (not a good idea), the scientist determined that the unfrozen pool tasted saltier than the partially frozen one. The scientist thought perhaps salt water had a lower freezing point than fresh water, and she decided to go home and try an experiment to see if this were true. So far, the scientist has identified a question, gathered a small amount of data, and suggested an explanation. In order to test this hypothesis, the scientist will conduct an experiment during which she can make accurate observations.

For the experiment, the scientist prepared two identical containers of fresh water and added some salt to CK12 Screenshot 1-1-300.png one of them. A thermometer was placed in each liquid and these were put in a freezer. The scientist then observed the conditions and temperatures of the two liquids at regular intervals.

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The scientist found support for the hypothesis from this experiment; fresh water freezes at a higher temperature than salt water. Much more support would be needed before the scientist would be confident of this hypothesis. Perhaps she would ask other scientists to verify her work.

In the scientist's experiment, it was necessary that she freeze the salt water and fresh water under exactly the same conditions. Why? The scientist was testing whether or not the presence of salt in water would alter its freezing point. It is known that changing air pressure will alter the freezing point of water, so this and other variables must be kept the same, or they must be controlled variables.

Example 1.1.1

In the experiment described above, identify the:

independent variable(s)
dependent variable(s)
controlled variable(s)

Solution:

Remember, the independent variable is what the scientist changed in his/her experiment. In this case, the scientist added salt to one container and not to another container. The independent variable is whether or not salt was added.
Dependent variables are what we look for as a result of the change we made. The scientist recorded the temperature and physical states (liquid or solid) over time. These are the dependent variables.
Controlled variables are kept the same throughout all of the trials. The scientist selected identical containers, put the same amount of water in the containers, and froze them in the same conditions in the same freezer. These are all controlled variables.

Suppose you wish to determine which brand of microwave popcorn (independent variable) leaves the fewest unpopped kernels (dependent variable). You will need a supply of various brands of microwave popcorn to test and you will need a microwave oven. If you used different brands of microwave ovens with different brands of popcorn, the percentage of unpopped kernels could be caused by the different brands of popcorn, but it could also be caused by the different brands of ovens. Under such circumstances, the experimenter would not be able to conclude confidently whether the popcorn or the oven caused the difference. To eliminate this problem, you must use the same microwave oven for every test. By using the same microwave oven, you control many of the variables of the experiment. What if you allowed the different samples of popcorn to be cooked at different temperatures? What if you allowed longer heating periods? In order to reasonably conclude that the change in one variable was caused by the change in another specific variable, there must be no other variables in the experiment. All other variables must be kept constant or controlled.

When stating the purpose of an experiment, it is important to clarify the independent and dependent variables. The purpose is frequently stated in a sentence such as:

"To see how changing ________ affects ______________."

in which the independent variable is listed in the first line and the dependent variable is listed in the second blank.

In the popcorn experiment, we would state the purpose as: "To see how changing the brand of popcorn affects the percentage of unpopped kernels". The independent variable is the brand of popcorn and the dependent variable is what percentage of the popcorn didn't pop. In the salt water experiment described earlier, we would state the purpose as "To see how adding salt to water affects the temperature the water freezes."

Lesson Summary

Scientists use experimentation to test their ideas.
In an experiment, it is important to include only one independent variable (to change only one thing in the experiment)
The dependent variable is what is measured or observed as a result of how the independent variable changed.
Controlled variables are those which are kept the same throughout various trials in the experiment.

Vocabulary

Experiment: A controlled method of testing a hypothesis
Controlled experiment: An experiment that compares the results of an experimental sample to a controlled sample.