This is what many people would picture as a scientist. Others picture a mysterious person walking around a laboratory full of strange glassware in a white lab coat and safety glasses! But what is a "real" scientist like? Generally, real scientists are disciplined professionals, and scientific investigations are very organized and methodical.
Investigations in Science
Investigations are at the heart of science. They are how scientists add to scientific knowledge and gain a better understanding of the world. Scientific investigations produce evidence that helps answer questions. Even if the evidence cannot provide answers, it may still be useful. It may lead to new questions for investigation. As more knowledge is discovered, science advances.
Steps of a Scientific Investigation
Scientists investigate the world in many ways. In different fields of science, researchers may use different methods and be guided by different theories and questions. However, most scientists follow the general steps outlined in the Figure below. This approach is sometimes called the scientific method. Don't let the word "method" fool you! Keep in mind that the scientific method is a general approach and not a strict sequence of steps. For example, scientists may follow the steps in a different order. Or they may skip or repeat some of the steps. No matter how the scientific method is followed, one step will follow logically from the previous, and they all lead to an answer to a question, and the process is designed to provide (as far as possible) answers that are reliable and testable.
Credit: W S Kershaw
License: CC BY-NC 3.0
The steps of the scientific "method" pictured here are not to be taken as a recipe. Scientific investigation can take many different forms and pathways, but this scheme is an attempt to illustrate a general approach that is common to most scientific investigations.
A scientific investigation, or experiment, is usually preceded by an observation or a question about the natural world. Having done as much research as possible about the question, one would then continue to the next phase - the hypothesis.
The central process is hypothesis formation. A hypothesis is a proposed answer to a question; what you think might happen. It is usually framed as an "if...then" statement. A hypothesis that Galileo might have used would say: If I drop two objects with different weights at the same time, they will hit the ground at the same time.
The "if" part of the hypothesis focuses and directs the investigation. Drop two object of differnt weights from the tower at the same time.
The "then" part helps to ensure that the experiement will lead to valid results. They either hit the ground at the same time or they don't.
Using the Scientific Method
Aristotle (refer to previous section) had a theory of gravity. He thought that heavy objects would fall faster than lighter objects. Aristotle's ideas carried such weight that for a long time this idea was accepted as true. In the late 1500's Galileo was doing ground breaking work in science and mathematics. He had a different idea about gravity. He thought that all objects would fall at the same rate regardless of their weight. The difference between Galileo and Aristotle is that Galileo, unlike Aristotle, would subject his hypothesis to testing. Fortunately, there was a special building close at hand - the Leaning Tower of Pisa. Because it was leaning, it was an ideal platform from which to drop objects. Galileo carried out his experiments, dropping different weight objects from the Tower and showed by experimentation that all objects do indeed fall at the same rate, regardless of their weight.
In our common experience this appears not to be true, but this is due to air resistance slowing the rate of fall of an object. If air resistance is eliminated, or taken into account, all objects do indeed fall at the same rate regardless of their weight. Galileo used spheres of about the same size (to reduce the influence of air rresistance) but differeing weights to test his hypothesis.
This link shows a recreation of the (perhaps) experiment carried out by Galileo: http://www.youtube.com/watch?v=_Kv-U5tjNCY
The following link shows the dropping of a feather and a hammer on the moon where there is no atmosphere to slow down the feather. Go here (http://www.youtube.com/watch?v=KDp1tiUsZw8http://www.youtube.com/watch?v=KDp1tiUsZw8) to see Galileo's hypothesis tested on the moon.
One of the most important aspects of experimental design is to design the experiement so that it produces useful results. Suppose you wanted to determine if plants would grow better if watered with old dish water rather than regular water. If you were to simply take a plant and water it with dish water, what could you say? If it died, could you say that the dishwater killed it? Perhaps it was a sick plant, or it was too cold for the plant, or the soil was not good, or there wasn't enough light for the plant to grow, or..... You get the picture. This experiment would not produce any useful results.
To design an experiment that will give useful results we need to ensure that what is used to water the plants is the only variable in the experiment. It is clear that more than one plant should be used, and that all the plants need to be the same and treated the same way: same pots, same soil, same amount of light, same temperature and so on. All the variables that could affect the outcome of the experiment need to be eliminated as variables. In this case the only variable (the experimental varaiable) is using dishwater to water the plants, and the control will be using regular water to water the plants. From a design point of view, the plants are divided into two groups. Both groups are treated exactly the same way except for the experimental variable. One group receives a measured amount of regular water (control group) and the other group receives the same amount of dishwater (experimental group). Under these conditions, any difference in the growth of the plants can be attributed to the difference in the water used on the plants. This design is followed in the design of all scientific experiments.