experimental technique - controlled experiment.

This is a controlled experiment. All variables are the same for each test tube except for the type of water.

It is impossible to conclude that the heat of the sun killed the plants and that their death was not due to the boiled water.

Since both test tubes received the same amount of sunlight it is difficult to reach the conclusion that the heat, due to the sunlight, is responsible for the death of the plants.

Since this is a controlled experiment we can say that the evidence points to one variable and that is the boiled water. Further testing may be needed.

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A controlled experiment is one in which a fair comparison or test is made during an investigation.

A variable is a factor that can influence the results of an experiment.

Experimental technique Controlled experiments
Irene was asked to design a controlled experiment to answer the question "Can water that had previously been boiled for at least ten minutes sustain life?" A controlled experiment is one in which only one variable is allowed to change from one test to another. Click for an example of how the words control and variable are used in a scientific investigation. Lets see. What are the variables in this experiment? 1) Size of test tube 2) Amount of water in both test tubes 3) Types of plants used and their size and health. 4) Amount of sunlight each receives. 5) The type of water (previously boiled or not) used. In an experiment we have three types of variables, the independent, the dependent variables and extraneous variables. An independent variable is changed by the experimenter and the dependent variable changes as a result of changes made to the independent variable. When graphing results the dependent variable is always represented by the y-axis while the independent variable is represented by the x-axis. Simply put the independent variable is what is changed while the dependent variable is what is measured or changes. Extraneous variables are variables that influence the outcome of an experiment but are not the variable that we are interested in. For example, a student wished to see whether a particular sports drink can increase performance. The student placed people into two groups, one is given the sport drink and one is not while performing the same exercises. Heart rate is then measured. An extraneous variable might be the average fitness of each group. If one group happened to have fitter people in it then the results would be distorted due to fitness rather than the sports drink. We collect data by measuring the changes to the independent variable. The independent variable in this experiment is the water. One test tube has water that had been previously boiled and the other has normal tap water. The dependent variable here is the length of the plant. Notice how all other variables remain the same in each test tube. For example: -The same amount of water is used for both test tubes. -The same type of plants of identical starting length are used. -Identical periods of sunlight for both test tubes. -Identical test tubes are used. Let's see how she conducts her experiment.
She placed identical plants in sealed test tubes as shown on the right. One test tube had boiled water obtained from the tap while the other had normal water from the same tap. After observing the outcome she concluded "It is the heat of the sun that killed the plants. The boiled water had no impact on the survival of the plants." Is this a controlled experiment? Do you agree with her conclusion? Explain. Solution
A year 7 student performed an experiment to find out which materials created the greatest friction. Click to see the experiment and answer the questions on whether this was a fair test.
Exercises Continue
1) A variable that is changed by a scientist during an experiment is called the
2) A researcher conducted an experiment to see if drinking 80 mL of water every hour lessens the chance of getting a headache as opposed to drinking only during a lunch break. The dependent variable in this experiment was
3) A researcher wanted to see how blood pressure in Humans changes as a response to stress. She organised four groups of ten similar individuals. She delivered a mild electric shock to individuals every half hour and then measured their heart rate after ten minutes. Group A received no shock, group B received a mild shock, group C received a medium level shock and group D received a severe shock. a) What is the independent variable? b) What is the dependent variable c) How should the researcher display her results on a graph?
4) A true experiment does not involve:
5) A scientist wanted to test how effective a vaccine is in preventing people from getting the flu. She setup two similar groups of people one group was given the vaccine and the other was not. a) The group that does not receive the vaccine is known as the b) Each group should have people with similar
6) Which of the following is NOT involved in an experiment?
7) In an experimental study, the scientist manipulates the ____ variable and measures the ____ variable. 8) In order to establish a clear relationship between two variables, it is necessary to eliminate the influence of
9) A researcher graphs the number of accidents in a particular year versus the speed of the car involved. The graph is shown on the right. a) The dependent variable is ____________________ b) The independent variable is ____________________ c) Is there a clear relationship between speed and the chance of having an accident? Explain. Solution