three constants in an experiment

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What Is a Control Variable? Definition and Examples

A control variable is any factor that is controlled or held constant during an experiment . For this reason, it’s also known as a controlled variable or a constant variable. A single experiment may contain many control variables . Unlike the independent and dependent variables , control variables aren’t a part of the experiment, but they are important because they could affect the outcome. Take a look at the difference between a control variable and control group and see examples of control variables.

Importance of Control Variables

Remember, the independent variable is the one you change, the dependent variable is the one you measure in response to this change, and the control variables are any other factors you control or hold constant so that they can’t influence the experiment. Control variables are important because:

• They make it easier to reproduce the experiment.
• The increase confidence in the outcome of the experiment.

For example, if you conducted an experiment examining the effect of the color of light on plant growth, but you didn’t control temperature, it might affect the outcome. One light source might be hotter than the other, affecting plant growth. This could lead you to incorrectly accept or reject your hypothesis. As another example, say you did control the temperature. If you did not report this temperature in your “methods” section, another researcher might have trouble reproducing your results. What if you conducted your experiment at 15 °C. Would you expect the same results at 5 °C or 35 5 °C? Sometimes the potential effect of a control variable can lead to a new experiment!

Sometimes you think you have controlled everything except the independent variable, but still get strange results. This could be due to what is called a “ confounding variable .” Examples of confounding variables could be humidity, magnetism, and vibration. Sometimes you can identify a confounding variable and turn it into a control variable. Other times, confounding variables cannot be detected or controlled.

Control Variable vs Control Group

A control group is different from a control variable. You expose a control group to all the same conditions as the experimental group, except you change the independent variable in the experimental group. Both the control group and experimental group should have the same control variables.

Control Variable Examples

Anything you can measure or control that is not the independent variable or dependent variable has potential to be a control variable. Examples of common control variables include:

• Duration of the experiment
• Size and composition of containers
• Temperature
• Sample volume
• Experimental technique
• Chemical purity or manufacturer
• Species (in biological experiments)

For example, consider an experiment testing whether a certain supplement affects cattle weight gain. The independent variable is the supplement, while the dependent variable is cattle weight. A typical control group would consist of cattle not given the supplement, while the cattle in the experimental group would receive the supplement. Examples of control variables in this experiment could include the age of the cattle, their breed, whether they are male or female, the amount of supplement, the way the supplement is administered, how often the supplement is administered, the type of feed given to the cattle, the temperature, the water supply, the time of year, and the method used to record weight. There may be other control variables, too. Sometimes you can’t actually control a control variable, but conditions should be the same for both the control and experimental groups. For example, if the cattle are free-range, weather might change from day to day, but both groups have the same experience. When you take data, be sure to record control variables along with the independent and dependent variable.

• Box, George E.P.; Hunter, William G.; Hunter, J. Stuart (1978). Statistics for Experimenters : An Introduction to Design, Data Analysis, and Model Building . New York: Wiley. ISBN 978-0-471-09315-2.
• Giri, Narayan C.; Das, M. N. (1979). Design and Analysis of Experiments . New York, N.Y: Wiley. ISBN 9780852269145.
• Stigler, Stephen M. (November 1992). “A Historical View of Statistical Concepts in Psychology and Educational Research”. American Journal of Education . 101 (1): 60–70. doi: 10.1086/444032

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What Is a Variable in Science?

Understanding Variables in a Science Experiment

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Variables are an important part of science projects and experiments. What is a variable? Basically, a variable is any factor that can be controlled, changed, or measured in an experiment. Scientific experiments have several types of variables. The independent and dependent variables are the ones usually plotted on a chart or graph, but there are other types of variables you may encounter.

Types of Variables

• Independent Variable: The independent variable is the one condition that you change in an experiment. Example: In an experiment measuring the effect of temperature on solubility, the independent variable is temperature.
• Dependent Variable: The dependent variable is the variable that you measure or observe. The dependent variable gets its name because it is the factor that is dependent on the state of the independent variable . Example: In the experiment measuring the effect of temperature on solubility, solubility would be the dependent variable.
• Controlled Variable: A controlled variable or constant variable is a variable that does not change during an experiment. Example : In the experiment measuring the effect of temperature on solubility, controlled variable could include the source of water used in the experiment, the size and type of containers used to mix chemicals, and the amount of mixing time allowed for each solution.
• Extraneous Variables: Extraneous variables are "extra" variables that may influence the outcome of an experiment but aren't taken into account during measurement. Ideally, these variables won't impact the final conclusion drawn by the experiment, but they may introduce error into scientific results. If you are aware of any extraneous variables, you should enter them in your lab notebook . Examples of extraneous variables include accidents, factors you either can't control or can't measure, and factors you consider unimportant. Every experiment has extraneous variables. Example : You are conducting an experiment to see which paper airplane design flies longest. You may consider the color of the paper to be an extraneous variable. You note in your lab book that different colors of papers were used. Ideally, this variable does not affect your outcome.

Using Variables in Science Experiment

In a science experiment , only one variable is changed at a time (the independent variable) to test how this changes the dependent variable. The researcher may measure other factors that either remain constant or change during the course of the experiment but are not believed to affect its outcome. These are controlled variables. Any other factors that might be changed if someone else conducted the experiment but seemed unimportant should also be noted. Also, any accidents that occur should be recorded. These are extraneous variables.

Variables and Attributes

In science, when a variable is studied, its attribute is recorded. A variable is a characteristic, while an attribute is its state. For example, if eye color is the variable, its attribute might be green, brown, or blue. If height is the variable, its attribute might be 5 m, 2.5 cm, or 1.22 km.

• Earl R. Babbie. The Practice of Social Research , 12th edition. Wadsworth Publishing, 2009.
• What Is a Dependent Variable?
• What Is an Experiment? Definition and Design
• Six Steps of the Scientific Method
• Examples of Independent and Dependent Variables
• How To Design a Science Fair Experiment
• The Role of a Controlled Variable in an Experiment
• Scientific Variable
• What Are the Elements of a Good Hypothesis?
• Dependent Variable vs. Independent Variable: What Is the Difference?
• What Is the Difference Between a Control Variable and Control Group?
• Independent Variable Definition and Examples
• Null Hypothesis Examples
• What Is a Controlled Experiment?
• DRY MIX Experiment Variables Acronym
• Scientific Method Vocabulary Terms
• What Is the Difference Between Hard and Soft Science?

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Experimental Design - Independent, Dependent, and Controlled Variables

Scientific experiments are meant to show cause and effect of a phenomena (relationships in nature).  The “ variables ” are any factor, trait, or condition that can be changed in the experiment and that can have an effect on the outcome of the experiment.

An experiment can have three kinds of variables: i ndependent, dependent, and controlled .

• The independent variable is one single factor that is changed by the scientist followed by observation to watch for changes. It is important that there is just one independent variable, so that results are not confusing.
• The dependent variable is the factor that changes as a result of the change to the independent variable.
• The controlled variables (or constant variables) are factors that the scientist wants to remain constant if the experiment is to show accurate results. To be able to measure results, each of the variables must be able to be measured.

For example, let’s design an experiment with two plants sitting in the sun side by side. The controlled variables (or constants) are that at the beginning of the experiment, the plants are the same size, get the same amount of sunlight, experience the same ambient temperature and are in the same amount and consistency of soil (the weight of the soil and container should be measured before the plants are added). The independent variable is that one plant is getting watered (1 cup of water) every day and one plant is getting watered (1 cup of water) once a week. The dependent variables are the changes in the two plants that the scientist observes over time.

Can you describe the dependent variable that may result from this experiment? After four weeks, the dependent variable may be that one plant is taller, heavier and more developed than the other. These results can be recorded and graphed by measuring and comparing both plants’ height, weight (removing the weight of the soil and container recorded beforehand) and a comparison of observable foliage.

Using What You Learned: Design another experiment using the two plants, but change the independent variable. Can you describe the dependent variable that may result from this new experiment?

Think of another simple experiment and name the independent, dependent, and controlled variables. Use the graphic organizer included in the PDF below to organize your experiment's variables.

High Resolution Version for Printing

Citing research references.

When you research information you must cite the reference. Citing for websites is different from citing from books, magazines and periodicals. The style of citing shown here is from the MLA Style Citations (Modern Language Association).

When citing a WEBSITE the general format is as follows. Author Last Name, First Name(s). "Title: Subtitle of Part of Web Page, if appropriate." Title: Subtitle: Section of Page if appropriate. Sponsoring/Publishing Agency, If Given. Additional significant descriptive information. Date of Electronic Publication or other Date, such as Last Updated. Day Month Year of access < URL >.

Here is an example of citing this page:

Amsel, Sheri. "Experimental Design - Independent, Dependent, and Controlled Variables" Exploring Nature Educational Resource ©2005-2024. November 3, 2024 < http://www.exploringnature.org/db/view/Experimental-Design-Independent-Dependent-and-Controlled-Variables >

Exploringnature.org has more than 2,000 illustrated animals. Read about them, color them, label them, learn to draw them.

Understanding Constants In An Experiment

• December 11, 2020
• Science Facts

Constants In An Experiment

The term ‘constant’ is used to refer to a particular quantity which is not intended to alter or change.

What are Constants?

Amongst the other fields, constants are also used in during various situations of an experiment. Such constants which are implemented in experiments are referred to as experimental constants.

Like other constants, experimental constants are also measurable. However, they cannot be changed in the due course of the experiment or in-between them.

There are various values which are considered as constants during experiments.

Constituents of natural forces such as the speed of light or the atomic weight of gold are considered as experimental constants.

Additionally, there are various properties which are considered to be experimental constants. The prime example of this is the boiling point of water.

The boiling point of water depends may alter depending on the altitude and the decrease in acceleration due to gravity.

However, experiments involving water in a single location consider its boiling point as constants.

The Need for Constants

There are various reasons why we need to implement constants within our experiments. However, they all stem out from the same characteristic, that is duplication of results or consistency in results.

Whenever we perform any experiment, we do so carefully ensuring that the process can be duplicated again as required.

If we involved a plethora of variables it would that we would receive a ton of variable results as well. This would completely defeat the purpose of experimenting.

Factors Considered as Constant in an Experiment

When we are on a lookout for constants, we essentially look for such factors which are considered to be similar in all states or conditions.

Irrespective of the time or the nature of this aforementioned factor, it will never change its state.

This stems out from the fact that a constant never changes its state in the duration of an experiment.

Understanding a constant becomes easier when one contrasts the constant factor with a mathematical constant.

In the field of mathematics, a constant refers to a particular factor which has a fixed numerical value.

In the same way, a constant in an experiment does not change its state and is universally equal all-around.

The only situation in which a mathematical constant and an experimental constant differ is that a mathematical constant does not involve any physical measurement.

Examples of Constants in Experiments

When you consider the factors used for determining an experimental constant, there are various constants that you might come across.

A few good examples of experimental constants include:

• The acceleration due to gravity
• Gravitational constant
• Avogadro’s constant
• The Gas constant
• Boltzmann’s constant
• The Stefan-Boltzmann constant
• Elementary charge
• Electron rest mass
• Proton rest mass
• Unified atomic mass unit
• Solar constant, and much more.

Apart from these constants, there are various other factors which are also considered as constants like Planck’s constant, the permittivity of free space, etc.

In essence, if you want to determine whether or not a particular factor is considered as a constant, you might want to think about such factors which contain a form of measurement that is universal.  

Constants In A Scientific Method

The term scientific method refers to an approach seeking a particular form of knowledge involving the formulation of a hypothesis or testing for proving its validity.

More often than not, scientific methods require intense experimentation for proving their validity. And such experiments often involve constants.

You might ask the purpose of constants in scientific methods. Here’s why we need them.

Whenever you need to perform experiments, you need to test through various factors which often involve a lot of measurable change.

These changes occur due to the presence of the dependent variable. As a result, the changes occurring allude to the dependent variable.

To understand such changes, the experimenters often introduce an independent variable for creating changes in the dependent variables.

However, there should always be only a single independent variable in such experiments.

Even other factors such as the presence of other variables are included in the form of controlled variables. And this is known as a constant in a scientific method.

Controls or Controlled Variables

Now, when you encounter the term ‘variable’, you might refer to such factors which are constantly found to be changing during an experiment. And you are right as well.

For the definition of a variable, states that any factor, trait, or condition which is found to exist in different amounts or types is a variable.

As a result, it would be correct to not refer to them as constants, right? Well, not exactly.

There are various situations in which variables are considered as constants. There are certain experiments in which a person performing the experiments considers certain variables in a constant state.

Such variables are referred to as controlled variables. As a result of this, the experimenter can attain more clarity in isolating the relationship between the independent variables and the dependent variables.

Moreover, by considering certain variables as constants, experimenters are also able to achieve constants results whenever they experiment.

The Prime Example of Controlled Variables

In the due course of an experiment, there are various variables which an experimenter considers to be constant.

The prime example of such controlled variables is the boiling point of water.

As aforementioned in the introductory paragraph, the boiling point of water variably changes when factors such as altitude and the acceleration due to gravity are involved in the experiment.

In spite of this, the temperature is considered constant as it allows the experimenter to derive constant results for a particular location or space.

Other Examples of Controlled Variables

Apart from the boiling point of water, there are various other examples which beautifully explain the concept of controlled variables within experiments.

A few of these include:

• The amount of fertilizer which a plant uses for the crop outgrowth.
• The type of soil is used for planting a particular type of plant.
• The amount of time which is spent by children in trying to learn a new concept.
• The amount of sunlight which a plant uses for its growth.

In spite of these examples, there are cases in which you might feel confused regarding controlled variables.

In simple terms, a controlled variable is referred to as determiners which greatly influence the result.

Usually, experimenters are more focused on understanding whether or not control variables have any significant effects on results.

With the help of control variables, they can do the same while achieving the desired results or outcomes in a particular experiment.

The Control Group

The term ‘control group’ essentially refers to a particular standard used for making comparisons in a particular experiment.

Whenever an experimenter stages an experiment, he or she designs it, particularly to include a control group and one or more experimental groups.

In an ideal sense, both the experimental groups and the control groups are similar.

However, the dissimilarity arises between these groups when the experimental group is subjected to various treatments which are believed to affect the outcome of the treatment.

Conversely, the control group isn’t subjected to any form of treatment or intervention which could affect the outcomes arising from the treatment.  

The Need For A Control Group

When you think about the involvement of a control group within the confinements of an experiment, you might think about the need which gives birth to such a need.

The primary reason why we need a control group is for the experimenters to easily be able to conclude a particular study.

It is only with the help of a control group that experimenters can determine whether or not a particular experiment can have a significant effect on the experimental group that can be recorded.

Moreover, the inclusion of a constant group within an experiment also ensures that the possibilities of making errors during the derivation of results are vastly minimized.

The Differences Between Constants and Controls

People often get confused with the different concepts that are involved with constants and controlled variables.

This is not only because they both begin with the same alphabet and that they sound the same, but it is also due to the similarity in their definitions.

However, you can be assured that these concepts don’t define the same things.

When we talk about constants, we essentially talk about the factors that are non-varying.

These factors are universally fixed and defined so that they are unable to start any changes that occur at the time of the results.

However, the purpose of control or a controlled variable isn’t the same.

Unlike a constant, a control or controlled variable is set aside to ignore the occurrence of any changes in the result that rise from the independent variable.

This ensures that the experimenter can view the experiment from an objective point of view.

When experimenters implement an experimental method, they do so understandingly which variables are controls and which of them are constants.

It is only by differentiating the controls and the constants that they can understand the changes occurring in the dependent variable.

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What Is a Constant in the Scientific Method?

Can a Science Experiment Have Two Manipulated Variables?

The scientific method forms the foundation of the collective knowledge of the world around us. It is how researchers figure out what is likely true in nature. A scientific method experiment begins with a hypothesis, which is an informed opinion that explains why certain things occur the way they do. In science, hypotheses lead to predictions. These are measurable events that occur during an experiment if the hypothesis is true. The most significant components of the scientific method include hypotheses, dependent and independent variables, constant variables and control groups.

TL;DR (Too Long; Didn't Read)

A constant variable is an aspect of an experiment that a scientist or researcher keeps unchanged. There can be more than one constant in an experiment.

Through rigorous experimentation and corroboration, which requires other scientists to duplicate the same result as the first, a scientist's hypothesis is either confirmed or proven incorrect. While many people think of only men and women in white lab coats using the scientific method, it is an intuitive process. If you've ever asked yourself whether something is true or why something is the way it is—why is the sky blue?—you've performed the first step of the scientific method.

Why the Scientific Method Is Important

There is a good reason teachers introduce the scientific method early in a science class. It's the most important fundamental tool of science. Without the scientific method, there would be no way for scientists to agree on what is likely true and what is not.

The term "science" comes from the Latin word for "knowing." The scientific method is the process used to know that a new idea is valid. The confirmation of these new ideas has both theoretical and practical implications. For example, they can increase our knowledge of the universe and how it works. New ideas can lead to the development of inventions that change how people live.

There are three types of variables used in scientific experiments: constant, independent and dependent.

A constant variable is any aspect of an experiment that a researcher intentionally keeps unchanged throughout an experiment.

Experiments are always testing for measurable change, which is the dependent variable. You can also think of a dependent variable as the result obtained from an experiment. It is dependent on the change that occurs. Scientists introduce an independent variable to an experiment to create a change in the dependent variable. There can only be one independent variable in each experiment, but there will normally be many constant variables.

To illustrate a constant variable by looking at an example, let's say a new drug comes out that claims to make it easier to lose weight. Each scientific experiment can only focus on one independent variable or make one change at a time. If researchers gave a group of people this new drug and also increased the amount of exercise each person in the study did, it would complicate the picture. Scientists wouldn't be able to tell whether the pill or the exercise was responsible for any changes in weight, the dependent variable.

To ensure that only one independent variable exists, everything else is held constant. So, the constant variables in this experiment investigating the effects of the diet pill would be variables like the number of calories consumed by each participant, the amount of exercise they get, how much sleep they receive, etc. The constants are all the other aspects that are held the same for each participant.

Difference Between a Control and a Constant

You may think that a constant is the same thing as a control, but there is a difference. A control is specifically set aside without any changes to give the researcher an objective picture of any changes in the independent variable. For studies of drugs, a placebo is the control. A person is not told whether they're taking a diet pill or a placebo. A control negates the possible effects of persons believing they are taking diet pills when they are not.

When using the experimental method, it is critical to understand which variables are constants and which are controls. This helps to ensure any changes to the dependent variable are a result of the independent variable alone.

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