Eleanor Finch
Controlled experiments are an essential tool in scientific research, allowing investigators to isolate and understand the impact of specific variables on outcomes. To qualify as a controlled experiment, the study must meet several criteria: the presence of at least two groups, with one acting as a control and remaining untouched by the experimental variable, the repetition of the experiment to ensure accurate results, and a slow and meticulous pace to facilitate careful observation and data processing. These controlled experiments are a cornerstone of the scientific method, enabling researchers to make robust, evidence-based conclusions.
| Characteristics | Values |
|---|---|
| Number of groups | At least two |
| Control group | Yes |
| Experimental group | Yes |
| Pace of experiment | Slow |
| Repetition | Multiple times |
| Variables | One or more |
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What You'll Learn
Control and experimental groups
The control and experimental groups should be as similar as possible, with the only difference between them being the presence or absence of the independent variable. This ensures that any differences in the outcomes between the two groups can be attributed solely to the presence of the independent variable in the experimental group. The experimental group is manipulated to try and change the outcome of the experiment, while the control group is kept as natural or unchanged.
In some cases, a control group may take a placebo, which is a substance or treatment that has no active ingredients or effect. This can be used to rule out the possibility that any changes observed in the experimental group are due to the participants' expectations or beliefs about being treated. However, the use of placebos can also introduce the placebo effect, where participants experience an effect or improvement simply because they believe there should be one.
It is important to note that not all experiments require a control group. However, control groups are critical to the scientific method as they help ensure the internal validity of a study. They allow researchers to isolate the effects of the independent variable and strengthen their ability to draw conclusions.
In summary, control and experimental groups are essential components of a controlled experiment, with the control group providing a baseline for comparison and the experimental group being manipulated to test the effects of the independent variable. By keeping all other variables constant between the two groups, scientists can confidently attribute any observed differences in outcomes to the presence of the independent variable.
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Constant variables
A controlled experiment is one that keeps all variables constant. A variable is any factor that can change value during an experiment, such as water temperature. Constants, on the other hand, are values that should not change either during or between experiments, such as the speed of light or the atomic weight of gold.
In a controlled experiment, the control group is matched with the experimental group except for one experimental variable. The control group is kept in an unchanging environment and is not of primary interest to the experimenter. It is important to keep the control group constant because any unexpected change in a control variable during an experiment would invalidate the correlation of dependent variables (DV) to the independent variable (IV), thus skewing the results.
A good example of a controlled experiment is one that tests the relationship between the amount of sunlight plants receive (independent variable) and subsequent plant growth (dependent variable). In this case, the control variable could be the amount of water the plants receive, the type of soil they are planted in, or the type of plant. By keeping these variables constant, the experimenter can directly attribute any changes in plant growth to the amount of sunlight received.
Another example of a controlled experiment is one that tests the relationship between pressure, volume, and temperature in the combined gas law. To do this, one of the variables (pressure, volume, or temperature) is kept constant while the others are changed. This allows the experimenter to quickly establish the relationship between the remaining variables.
In some cases, a property can be considered a constant for the purposes of an experiment even though it technically could change under certain circumstances. For example, the boiling point of water changes with altitude, but for experiments in one location, it can be considered a constant.
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Accurate results
Achieving accurate results is a key goal of a controlled experiment. To ensure accuracy, the experiment should be repeated multiple times. The more times the experiment is repeated with the same outcome, the more confident the researcher can be in the accuracy of the results.
Controlled experiments also aim to keep all variables constant, except for the one experimental variable. This is to ensure that any changes in the results are due to the variable being tested, and not other external factors. For example, in an experiment to test the effect of temperature on a reaction, all other factors, such as the concentration of reactants, should be kept constant.
The control group is an important feature of a controlled experiment. This group is not exposed to the experimental variable and is kept in an unchanging environment. By comparing the results of the control group to the experimental group, researchers can attribute any differences in the results to the experimental variable.
In some cases, it may be necessary to have multiple control groups. For example, in an experiment to test the effect of a new drug, there may be a control group that receives no treatment, and another control group that receives a placebo treatment. This helps to account for the psychological effects of receiving a treatment, sometimes known as the placebo effect.
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Pace of experiment
The pace of an experiment is an important factor in ensuring the validity of the results. A controlled experiment should proceed at a slow enough pace that the scientist can carefully observe all reactions and process all experimental data. This careful and deliberate approach helps to ensure that the results are accurate and not just random events.
For example, let's consider an experiment to determine whether sugar dissolves more quickly in warm or cold water. The scientist would need to take the time to carefully control all aspects of the experiment, such as the temperature, humidity, and air movement. They would also need to keep the number of stirs and the pressure applied constant across all trials. By proceeding at a slow and steady pace, the scientist can ensure that all variables are kept constant and that any changes observed are due to the independent variable being tested.
In another example, Louis Pasteur's famous experiment to answer the question, "Can microorganisms generate spontaneously?" involved a slow and methodical approach. Pasteur kept all factors the same, including temperature, wait time, and the kind of flask used. He then introduced a single variable, removing the neck of the flask to let air in, and carefully observed the results over time. This slow and controlled pace allowed Pasteur to make careful records of the results and ensure the accuracy of his findings.
The pace of an experiment is also important in studies involving living organisms, where growth or behavioural changes may occur over extended periods. For instance, in an experiment studying the growth of seedlings, the scientist may measure their growth over a period of two weeks, carefully observing and recording the changes over time. This slower pace allows for a more comprehensive understanding of the variables being studied.
In summary, the pace of a controlled experiment should be carefully considered to ensure the validity and accuracy of the results. By proceeding at a slow and deliberate pace, scientists can carefully control all variables, observe reactions, and process data effectively, ultimately leading to more robust and reliable findings.
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Observations and data
In the example of the student experiment investigating the effect of sawdust on plant growth, observations were made after a set number of days. The students recorded their observations about the seedlings in each group, growing in either potting soil or sawdust. These observations constitute valuable data that can be analysed to determine the impact of the growth medium on seedling development.
Similarly, in an experiment investigating enzyme activity, careful observations are made to record the time it takes for enzymes to digest gelatin. By using camera film, which turns from black to clear as gelatin is broken down, students can measure the time required for different enzymes to digest the gelatin. These observations provide data that can be used to understand the efficiency of various enzymes in breaking down gelatin.
Another example is an experiment to test the effect of temperature and light on the growth of seedlings. By growing seedlings under different light conditions and temperatures, observations on their growth over a period of two weeks are made. This data helps in understanding the impact of environmental factors on seedling growth.
In the context of scientific theories, Jane Goodall's collection of both qualitative and quantitative data during her studies of chimpanzee behaviour is noteworthy. Qualitative observations might include detailed descriptions of social interactions, while quantitative data could involve counting the number of chimpanzees in a group or measuring the duration of specific behaviours.
Overall, the observations and data gathered in a controlled experiment are essential for scientific inquiry. They provide evidence to support or refute hypotheses, contribute to the development of scientific theories, and enhance our understanding of the natural world.
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