Instruction 7-2
Hypothesis | Tools and Technology | Displaying Data | Written Reports and Oral Presentations | Summary

Conducting A Scientific Experiment  

The word experiment means a different thing to scientists than it does to most people. For example, you might tell your friend that you are going to experiment with a pizza recipe. You might plan to use tomatoes and jalapenos on a thin crust, or you might use steak and mushrooms on a thick crust. You might change the types of spices you include in your pizza sauce. This is not a scientific experiment; because you can’t know what effect the changes you make will have on the pizzas.

To scientists, an experiment is a procedure that tests a hypothesis. A scientist may test a hypothesis by gathering information under controlled conditions (http://antoine.frostburg.edu/chem/senese/101/intro/faq/controlled-conditions.shtml).

Sometimes scientists use two different groups in an experiment. These include a control group and an experimental group. In the control group, all the conditions are kept exactly the same. In the experimental group, all the conditions are kept the same except for the one being tested (http://skepdic.com/control.html).

Let’s say you are a scientist who is studying pumpkin size. You want to figure out whether feeding pumpkins milk instead of water will make them grow bigger. In your control group, you would plant pumpkin seeds in one kind of soil. You would keep the light, water, and fertilizer the same for all of these plants. You would water them all the same amount at the same time. In other words, you would keep all the conditions the same. These conditions are the controlled variables. 

In the experimental group, you keep most conditions, such as soil, light, and fertilizer, the same as the control group. You would change only one condition: you would use milk instead of water to water the plants. You would use the same amount of milk for each plant in this group.

The condition that you changed, substituting milk for water, is called the independent variable. This is because it is the only variable that changes the outcome. As you conduct your experiment, you measure and take notes about the condition of the plants. The plant condition is the dependent variable. This is because the changes to the condition depend on changes made to the independent variable.

Some experiments are not controlled. Let’s say you hypothesize about the feeding patterns of a species of rodents. To test your hypothesis, you might attach satellite transmitters to some of the rodents. Then you would be able to track their movements.


Tools

The type of experiment you conduct will determine what kinds of tools you need. For example, in the rodent experiment, the satellite transmitter is a tool. Here are some other examples of tools scientists use:

• A microscope is used to make small things visible. 

• A ruler measures lengths. 

• A chromatograph can measure pesticides that are found in plants and fishes. 

You need tools to measure, observe, and track changes. Tools include things like binoculars, thermometers, beakers, test tubes, hot plates, telescopes, scales, and computers. Tools are very important. If you don’t have the right tools to perform your experiment, you will have to throw away your hypothesis.  

Student Guide to Science Fair projects 
http://www.lkwdpl.org/study/sfair/  

Reading List:

for Students, Parents and Teachers

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