Experiments are systematic observations or measurements, preferably made under controlled conditions-that is, under conditions in which a single variable changes.Ĥ. After a hypothesis has been formed, scientists conduct experiments to test its validity. Unfortunately (or perhaps fortunately), this hypothesis does not lend itself to direct testing by any obvious experiment, but scientists can collect additional data that either support or refute it.ģ. For the disappearance of the dinosaurs, the hypothesis was that the impact of a large extraterrestrial object caused their extinction. Suitable experiments can be designed to choose between these two alternatives. the sun revolves around Earth every 24 hours. Earth rotates on its axis every 24 hours, alternately exposing one side to the sun, orī. For example, the observation that we experience alternating periods of light and darkness corresponding to observed movements of the sun, moon, clouds, and shadows is consistent with either of two hypotheses:Ī. ![]() The hypothesis may not be correct, but it puts the scientist’s understanding of the system being studied into a form that can be tested. After deciding to learn more about an observation or a set of observations, scientists generally begin an investigation by forming a hypothesis, a tentative explanation for the observation(s). ![]() For the question of the dinosaurs’ extinction, the initial observation was quantitative: iridium concentrations in sediments dating to 66 million years ago were 20–160 times higher than normal.Ģ. Examples of quantitative observations include the following: the melting point of crystalline sulfur is 115.21 degrees Celsius, and 35.9 grams of table salt-whose chemical name is sodium chloride-dissolve in 100 grams of water at 20 degrees Celsius. Quantitative observations are measurements, which by definition consist of both a number and aunit. Examples of qualitative observations include the following: the outside air temperature is cooler during the winter season, table salt is a crystalline solid, sulfur crystals are yellow, and dissolving a penny in dilute nitric acid forms a blue solution and a brown gas. Qualitative observations describe properties or occurrences in ways that do not rely on numbers. Observations can be qualitative or quantitative. This procedure consists of making observations, formulating hypotheses, and designing experiments, which in turn lead to additional observations, hypotheses, and experiments in repeated cycles (Figure 1.4.1).įigure 1.4.1: The Steps in the Scientific Method.ġ. Scientists search for answers to questions and solutions to problems by using a procedure called the scientific method.
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