(IES) Designing an Experiment - Developing a Hypothesis Lesson

Designing Experiments - Developing a Hypothesis

A hypothesis (plural: hypotheses ) is a prediction about the outcome of a scientific investigation. Like all predictions, hypotheses are based on a person's observations and previous knowledge or experience. In science, hypotheses must be testable. That means that researchers should be able to carry out an investigation and obtain evidence that shows whether the hypothesis is true or false. The way hypotheses are written is in the form of an If . . . then . . . 

Tips for Developing Good Hypotheses

  1. First, develop ideas for a hypothesis, write down several questions about the topic. Try to narrow the questions to one that can be investigated scientifically. Then write the hypothesis.
  2. Make sure the hypothesis is a prediction based off observations and previous knowledge or experience.
  3. Make sure the hypothesis can be tested through observations and measurement.
  4. Check the way you worded the hypothesis. A properly worded hypothesis should take the form of an If . . . then . . .

Variables in the Hypothesis

The hypothesis will usually mention the independent variable (IV) and the dependent variable (DV) and the relationship between the two. You will also want to consider the variables you can control. The control variables (CV) are the variables that remain the same.

Read the following Scenario.

Flora and her twin sister Fiona are both given a new basketball. The basketballs are exactly alike and the girls can't wait to get on the court to play. Fiona impatiently rushes her dad as he is pumping air into her new basketball. As soon as her dad stops to check the pressure she squeals, "it's good" unclipping the pump and screwing on the cap. Fiona is ready to play. Flora laughs while her dad begins to pump air into her basketball and she waits patiently while he checks the pressure and then adds more air before giving the ball to her. Flora notices her basketball seems to have more bounce than Fiona's. She thinks about why her basketball might have more bounce and she suspects it has something to do with the air in the ball.

Flora has written a scientific question. Does the amount of air pressure affect how high a standard basketball will bounce when dropped from a three foot stool?

Now Flora needs to make a prediction.

Based on her observation she writes a hypothesis: If the amount of air pressure in a basketball is increased then the basketball will bounce higher vertically when dropped.

An experiment starts and finishes with the factors that change during the experiment. These are the variables.

A variable is part of an experiment that can change. There are three main kinds of variables.

Independent variable - what is being changed or manipulated in an experiment.

The independent variable that is manipulated by the experimenter will have several different values, and these different values are called the levels of the independent variable. For example, if temperature were the independent variable in an experiment, then 10ºC, 20ºC, 30ºC, and 40ºC might be the different levels. Usually one of the levels of the independent variable is the reference point or "normal" value of the variable, and the other levels will be compared with this one in order to draw conclusions from the experiment. This reference level of the independent variable, which other levels will be compared to, is called the control for the experiment.

  • Dependent variable - what will be measured or observed, the responding variable
  • Controlled variable - also called the constant; these are the variables that the scientist want to be sure remains constant so that it will not have an affect that will change the outcome.

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