Knight’s 1806 experiment showed that plant roots grow in the direction of gravitational pull by growing plants in the rim of a spinning wheel. When you design your experiment, think of ways that you can change the force of gravity on a growing plant. Your experiment may be inspired by Knight’s wheel, or you could simply find ways to turn plants upside down or on their sides in order to observe changes in their growth. The more variables you include in your experiment, the more complicated it will be to analyze the results, so you may want to only include one or two variables.
However you decide to test the effects of gravity, be sure to include a “control” in your experiment for comparison. A control in an experiment is used to prove that the changes you observe are occurring because of the actions you are taking in the experiment. For example, if you decide to grow a plant in a container that has been turned upside down, your control might be to plant a second seed of the same variety, keeping it upright. You should treat your control plant exactly like the experimental plant in every way except its position, making sure that it gets the same amount of light and water.
You already know that plants respond to gravity while they are growing. You have also probably noticed that when plants grow, their stems and leaves point up out of the ground, while their roots grow down. Given what you already know, think about what you expect to happen to the plants in your experiment and why. Write down a sentence or two to describe your predictions. This statement is your hypothesis and it will help you focus your experiment on proving that prediction right or wrong.
After you’ve formed a hypothesis, it is time to begin your experiment and collect your data. Take frequent, accurate measurements to record the ways that your variables have affected the plants’ growth. It is important that you also measure the control plant when you measure the experimental plants in order to make accurate comparisons. This will allow you to accurately interpret the data when your experiment is over. Be sure to give yourself enough time to perform the experiment before your science fair deadline.
Now that you have concluded your experiment and collected all of your data, you should be able to see the ways that your variables have affected plant growth. Compare your results to the prediction you made in your hypothesis. Whether your predictions were proven correct or not, try to see if you can figure out why, based on the observations you made during your experiment. Finally, present your findings for your science fair according to your school’s guidelines.