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Variables Designing a fair experiment

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Page 1: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

VariablesDesigning a fair experiment

Page 2: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

What is a Variable?

• Scientists design experiments in which changes to one item cause something else to change in a predictable way.

• A variable is any factor, trait, or condition that can exist in differing amounts or types. An experiment usually has three kinds of variables:

• Controlled• Independent• Dependent

Page 3: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

Independent Variables

• The independent variable is purposefully changed by the scientist

• A good, fair test only has one independent variable

• Why is it important to only have one independent variable?

Page 4: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

Dependent Variables

• The dependent variable is caused by and depends on the independent variable.

• The scientist focuses his/her observations on how the dependent variable changes in response to the independent variable.

• Why is it necessary to observe the dependent variables?

Page 5: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

Example

The longer the amount of time spent studying causes an increase in test scores

Remember – independent variable is changed purposefully and the dependent variable changes in response

Independent Variable – time spent studying

Dependent Variable – test scores

Page 6: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

Controlled Variables

Controlled variables are values that a scientist wants to remain constant

They must be observed as closely as the dependent variables in order to maintain a fair test

There is usually more that one controlled variable Controlled variables are also known as constant variables Why does an experiment need controlled variables?

Page 7: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

Variables

In a good experiment, the independent and dependent variables are both measurable.

Time, mass, length are all examples of measurable values

Variables with no true unit of measure would be a poor variable to use in an experiment (i.e. – love, success)

Page 8: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

More Examples…

•Stirring

•Type of sugar

Amount of sugar that dissolves completely measured in grams

Temperature of water measured in degrees

Celcius

Does heating a cup of water allow it to absorb

more sugar?

•The faucet

•Water pressure

Amount of water flowing per minute measured in mL per

minute

Water faucet opening

•closed

•half open

•fully open

How much water flows through a faucet at different openings?

Controlled Variables

(What is kept the same)

Dependent Variable

(What is observed)

Independent Variable

(What is change)

Question

Page 9: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

Your turn….

• After studying about recycling, members of John’s Biology class investigated the effect of various recycled products on plant growth. John’s lab group compared the effect of different aged grass compost on bean plants. Each plant received the same amount of sunlight and water each day.

• Identify the controlled, independent and dependent variables.

Page 10: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

Answers…

Independent Variable

Amount of compost

Dependent Variable

Height of bean plant

Controlled Variables

Amount of sunlight

Amount of water

Page 11: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

The Role of Variables in the Scientific Method

Variables play an important part in the scientific method. A hypothesis is formatted according to the independent and

dependent variables. A graph (data analysis) is labeled according to the independent

and dependent variables Variables are further explained in the conclusion.

Page 12: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

Hypothesis

A hypothesis is a possible answer to a scientific question. It is NOT an educated guess.

A hypothesis should always be presented in the form of an “If…….then….. statement.”

“If” is followed by the independent variable, “then” is followed by the dependent variable.

Example - If a plant is grown in compost, then it will grow taller.

Page 13: Variables Designing a fair experiment. What is a Variable? Scientists design experiments in which changes to one item cause something else to change in

Hypothesis Practice

Independent Variable – time spent studying Dependent Variable – test grade

Independent Variable – light or dark Dependent Variable - # of earthworms

Independent Variable – fertilizer Dependent Variable – height of plant


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