Name: _____________________________________________ Date: ______ Period: ______ Pride: ______
HOW TO WRITE A HYPOTHESIS
A hypothesis is a tentative statement that proposes a possible explanation to some phenomenon or event. A useful
hypothesis is a testable statement, which may include a prediction. A hypotheses should not be confused with a theory.
Theories are general explanations based on a large amount of data. For example, the theory of evolution applies to all
living things and is based on wide range of observations. However, there are many things about evolution that are not
fully understood such as gaps in the fossil record. Many hypotheses have been proposed and tested.
When Are Hypotheses Used?
The key word is testable. That is, you will perform a test of how two variables might be related. This is when you are
doing a real experiment. You are testing variables. Usually, a hypothesis is based on some previous observation such as
noticing that in November many trees undergo color changes in their leaves and the average daily temperatures are
dropping. Are these two events connected? How? Any laboratory procedure you follow without a hypothesis is really
not an experiment. It is just an exercise or demonstration of what is already known.
How Are Hypotheses Written? Example: If the drop height of the raw egg increases, then the chance it will break
will increase because it will have an increased final velocity as it hits the ground.
Notice that this statements contains the words if, then, and because. They are necessary in a formalized hypothesis. But
not all if-then-because statements are hypotheses. For example, "If I play the lottery, then I will get rich because I think I
will win." This is a simple prediction. In a formalized hypothesis, a relationship is stated.
Formalized hypotheses contain two variables. One is "manipulated" and the other is "responding." The manipulated
variable is the one you, the "scientist" control and the responding variable is the one that you observe and/or measure the
results. In the example above, the variable that comes after the “if” is the manipulated variable, and the variable that
comes after the “then” is the responding variable. Be sure to explain why you chose your hypothesis by completing the
sentence with “because…”
The ultimate value of a formalized hypothesis is it forces us to think about what results we should look for in an
experiment. Complete the “Writing Hypotheses Practice Sheet” to try out a few hypotheses.
PRACTICE WRITING HYPOTHESES
Directions:
Write Hypotheses for the given situations in the space provided. Identify the dependent and independent variable for
each.
1. How does the amount of leaves on a tree affect how many birds will build nests in it?
Hypothesis: If ____________________________________________________,
then ____________________________________________________________
because __________________________________________________________.
2. How does the acid level of a lake affect how many fish live there?
Hypothesis: If ____________________________________________________,
then ____________________________________________________________
because __________________________________________________________.
3. How does the amount of milk you drink affect the strength of your bones?
Hypothesis: If ____________________________________________________,
then ____________________________________________________________
because __________________________________________________________.
4. Manipulated Variable: Length of paper helicopter blades
Responding Variable: Rotational speed
The student believes that as the blades get longer, the amount of distance they need to travel increases, so it will take
them longer to travel that distance.
Hypothesis: ______________________________________________________________________________________
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5. Manipulated Variable: Temperature of a solution
Responding Variable: Dissolving time of powdered drink mix
The students thinks that powdered mix will dissolve faster in a warmer solution because there of the higher average
kinetic energy in warm water.
Hypothesis: ______________________________________________________________________________________
________________________________________________________________________________________________
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6. Manipulated Variable: Depth of Lake Elkhorn
Responding Variable: Water temperature
The students research says that the deepest trenches in the ocean are filled with the coldest water, so the colder a lake,
the deeper it must be.
Hypothesis: ______________________________________________________________________________________
________________________________________________________________________________________________
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7. Manipulated Variable: Baseball batting practice
Responding Variable: Batting average
The student did observation (went to MLB batting practice) and found that Dustin Pedroia does batting practice for 1
hour before a game while Derek Jeter does it for 45 minutes.
Hypothesis: ______________________________________________________________________________________
________________________________________________________________________________________________
________________________________________________________________________________________________
8. Manipulated Variable: Number of recycling posters in school building
Responding Variable: Amount of aluminum cans found on school grounds
Hypothesis: ______________________________________________________________________________________
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