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How influential are Freud’s ideas in today’s society?
Hydrochloric acid uses
What properties make plastics harmful to people and the environment?
Pretest Direction: Give the meaning of the following. 1. Science = 2. Scientific laws = 3. Scientific principles =
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Find the acceleration of a 12.22 kg bicycle with 123 N of net force acting on it.
Find the acceleration of a 12.22 kg bicycle with 123 N of net force acting on it.
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2. at which site/s can contact metamorphism happen? 3. why are these sites probable places of metamorphism?
In science, a variable is any factor, trait, or condition that can exist in differing amounts or types.
Scientists try to figure out how the natural world works.To do this they use experiments to search for cause and effect relationships. Cause and effect relationships explain why things happen and allow you to reliably predict the outcomes of an action. Scientists use the scientific method to design an experiment so that they can observe or measure if changes to one thing cause something else to vary in a repeatable way.
These factors that change in a scientific experiment are variables.
A properly designed experiment usually has three kinds of variables: independent, dependent, and controlled.
What is an Independent Variable?
The independent variable is the one that is changed by the scientist. Why just one? Well, if you changed more than one variable it would be hard to figure out which change is causing what you observe. For example, what if our scientific question was: "How does the size of a dog affect how much food it eats?"; then, during your feeding experiments you changed both the size of the dog and the time of day the dogs were fed. The data might get a bit confusing— did the larger dog eat less food than the smaller dog because of his size or because it was the middle of the day and dogs prefer to eat more in the morning?
Sometimes it is impossible to just change one variable, and in those cases, scientists rely on more-complicated mathematical analysis and additional experiments to try to figure out what is going on. Older students are invited to read more about that in our Experimental Design for Advanced Science Projects page. To be clear though, for a science fair, it is usually wise to have only one independent variable at a time. If you are new to doing science projects and want to know the effect of changing multiple variables, do multiple tests where you focus on one independent variable at a time.
What is a Dependent Variable?
The dependent variables are the things that the scientist focuses his or her observations on to see how they respond to the change made to the independent variable. In our dog example, the dependent variable is how much the dogs eat. This is what we are observing and measuring. It is called the "dependent" variable because we are trying to figure out whether its value depends on the value of the independent variable. If there is a direct link between the two types of variables (independent and dependent) then you may be uncovering a cause and effect relationship. The number of dependent variables in an experiment varies, but there can be more than one.
What is a Control Variable?
Experiments also have controlled variables. Controlled variables are quantities that a scientist wants to remain constant, and she or he must observe them as carefully as the dependent variables. For example, in the dog experiment example, you would need to control how hungry the dogs are at the start of the experiment, the type of food you are feeding them, and whether the food was a type that they liked. Why? If you did not, then other explanations could be given for differences you observe in how much they eat. For instance, maybe the little dog eats more because it is hungrier that day, maybe the big dog does not like the dog food offered, or maybe all dogs will eat more wet dog food than dry dog food. So, you should keep all the other variables the same (you control them) so that you can see only the effect of the one variable (the independent variable) that you are trying to test. Similar to our example, most experiments have more than one controlled variable. Some people refer to controlled variables as "constant variables."
In the best experiments, the scientist must be able to measure the values for each variable. Weight or mass is an example of a variable that is very easy to measure. However, imagine trying to do an experiment where one of the variables is love. There is no such thing as a "love-meter." You might have a belief that someone is in love, but you cannot really be sure, and you would probably have friends that do not agree with you. So, love is not measurable in a scientific sense; therefore, it would be a poor variable to use in an experiment.
In some experiments, time is what causes the dependent variable to change. The scientist simply starts the process, then observes and records data at regular intervals.
When a scientist performs a test or survey on different groups of people or things, those groups define the independent variable. For example:
Sometimes a variable simply represents an either/or (binary) condition. For example, something might be either present or not present during an experiment.
Parts of a Controlled Experiment
A controlled experiment is an experiment in which the scientist changes/manipulates only one thing to observe and measure the effects of that one change. Below is an outline of the parts of every controlled experiment. In order to begin developing scientific questions for designing our own controlled experiments, we must fully understand the parts of every controlled experiment.
- Independent Variable (IV)/Experimental Group (EG): The one part of the experiment that is changed/manipulated or given different treatment by the scientist (cause).
- Dependent Variable (DV): The part of an experiment that changes in response to, or affected by, the independent variable. This change is what the scientist observes and measures throughout the experiment (effect).
- Constants (C): The parts of an experiment that are kept the same for all groups and trials to ensure a fair test.
- Control Group (CG): The group in an experiment that is “normal” or untreated to be compared with the experimental group. Keep in mind that there is not a control group in every experiment. There is only a control group if there is such thing as a "normal" or untreated condition.
Key words for Identifying the Parts of a Controlled Experiment
The following key words can help you to identify the parts of a controlled experiment.
- Independent variable – different, change, varied/various, compare, cause, manipulate, experimental group, experimental variable
- Dependent variable – measure, record, results, effect, outcome, response
- Constants – same, similar, identical, replicate, clone, copy
- Control Group – normal, untreated, natural, regular, typical
Re-watch the video below on the parts of a controlled Experiment:
Every controlled experiment investigates how an independent variable (the one thing changed by the scientist) has an effect on the dependent variable (what the scientist measures and observes).
In-Class Activity
Part I
1. Fill in the blanks to write the scientific, testable question under investigation FROM THE VIDEO.
What is the effect of the type of drink on _______________?
2. What is the independent variable in this controlled experiment? (from the video)
3. What is the dependent variable in this controlled experiment? (from the video)
4. What does "DRY MIX" stand for?
Part II
Take a look at the two scientific questions below. These questions were designed and tested by middle school students in New York City. They are not by any means perfect controlled experiments, but they do provide examples of how a student scientist studies how making one change (independent variable) has a measurable effect on something else (dependent variable). You may click on the question to see the details of the entire project. After reviewing these two projects, answer the questions that follow.
1. Identify the independent variable (IV), dependent variable (DV), constants (C), and control group (if there is one) for the two question above.
- What is the effect of air pressure on how high a basketball bounces?
- How does the amount of baking soda affect the the explosion of a volcano?
3. Rewrite the questions above, but replace the independent variable in the example with "IV", and dependent variable with "DV".
For example, "How does the amount of water affect the height of a fig plant?
"How does the (IV) affect the (DV) ?"