4-1.3 Summarize the characteristics of a simple scientific investigation that represent a fair test (including a question that identifies the problem, a prediction that indicates a possible outcome, a process that tests one manipulated variable at a time, and results that are communicated and explained).
Scientific Investigations
Essential Question: What are the characteristics of a simple scientific investigation that represents a fair test? Scientists ask questions about the world around them. Then they conduct studies to try to find answers. Sometimes scientists observe something in nature over time. That is one kind of study. Another kind is a carefully controlled test called an experiment. Kinds of Investigations An investigation is a careful study of something to try to answer a question about it. Scientists use different kinds of investigations. Sometimes they simply do research to gather information and answer their question. Often, after doing research, they conduct a test to answer their question. Which kind of investigation they choose depends on the questions they are trying to answer. Making a Prediction Suppose you observe that a puddle dries up quickly on a sunny summer day. You wonder how water evaporates, or turns from a liquid to a gas. You ask the questions, “How does sunlight affect the evaporation of water?” After scientists ask a question, they think of possible answers. They use what they already know to make a prediction that makes sense. Recall that a prediction is an inference about what will happen in the future. A prediction may also be an inference about what is true. What prediction would you make about how water evaporates? First, think about what you already know about water and sunlight. You might predict that sunlight makes water evaporate faster. Designing and Conducting an Experiment How do scientists find out if a prediction is correct? Often, they conduct an experiment – a carefully controlled test. Before starting an experiment, scientists design, or plan, all parts of the test. They list the materials they will need. The materials most often include science equipment and measuring tools. They also make a step-by-step plan telling exactly what they will do. How would you test your prediction about evaporation? Suppose you decide to fill two small bowls with water. You plan to place one bowl in sunlight and the other bowl in shade. The picture below shows the setup for your experiment. Part of planning an experiment is deciding what the variables will be. A variable is anything that can change, or vary, in an experiment. An experiment has different kinds of variables. Controlled variables are factors that a scientist keeps the same in all parts of an experiment. In your experiment, you will use two bowls that are the same size and shape. You will put the same amount of water in each bowl. You will let both bowls sit for the same amount of time. A manipulated variable is a factor that a scientist changes in different parts of an experiment. Whether or not the bowls get sunlight is the manipulated variable in your experiment. One bowl of water will get sunlight. The other one will not. A responding variable is a factor that may change when the manipulated variable is changed. The responding variable responds to the manipulated variable. In your experiment, the responding variable will be the amount of water that evaporates from each bowl. Suppose you let the bowls sit for three hours. At the end of that time, you measure the amount of water in each bowl. Then you compare the amounts. It is important to change only one factor in an experiment. Otherwise, you will not know the cause of any effects that you observe. A fair test is an experiment in which only one factor is changed or tested. What if you put more water in one bowl than the other, or the bowls you use have different shapes? Then your comparisons will not be fair. You must change only whether or not the bowls get sunlight. Recording Data and Stating a Conclusion When you conduct an experiment, you must record, or write down, your data. Remember that data are pieces of information. Data from an experiment include observations and measurements. The data from your experiment include the amount of water you put in each bowl and the amount of water left after three hours. You decide to show your data in a table. You make the table shown below. (You will learn more about displaying data in the next lesson.) Effect of Sunlight on the Evaporation of Water Location of Bowl Water at Start Water after 3 Hours Sunlight 200 mL 175 mL Shade 200 mL 195 mL Next, you must study the data. Then you can draw or state a conclusion. A conclusion is a statement about what data mean. The data in the table show that more water evaporated from the bowl that was in sunlight. You write a conclusion stating that sunlight makes water evaporate faster. You should also compare your results to your prediction. The data support your prediction. They help show that your prediction is correct. Whether or not this happens, you should repeat your experiment at least two more times. Then you can see if you get the same results each time. Results that can be repeated are more likely to be trusted as correct. Often, data does not support a prediction. That does not mean that an experiment is a failure. Scientists learn something from every experiment. They use what they learn to design and conduct new tests. |
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