23Grade 8 Science

(0Module 1, Lesson 3

Lesson 3

Scientific Inquiry

Vocabulary

• testable

question

• variable

• independent

variable

• dependentvariable

• hypothesis

• fair test

• controlledvariable

observations

source of error

Learning Outcomes

After completing this lesson you will be able to use the scientificinquiry process to conduct a fair test to determine factors thataffect flow within a given system. The process includes

• identifying variables

• creating a hypothesis

• planning and conducting an experiment

• making and recording observations

• analyzing data and making conclusions

• identifying possible sources of error

• reflecting on the process and identifying possible implicationsfor daily life

Factors that Affect Flow Rate

In the last two lessons you investigated and compared theviscosity of different fluids. You also found out that there aresome factors that can affect the viscosity of a particular fluid at agiven time. For example, pressure can cause a fluid to be more orless viscous. Have you ever wondered why milkshake strawshave a larger diameter? If you've tried to drink a milkshakethrough a straw with a smaller diameter, you would have foundyou have to work harder and apply more pressure to get themilkshake to flow through the straw as quickly as it would witha larger straw.

This next section will lead you through a science inquiry toinvestigate another factor that affects flow rate.

• conclusion

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Step One: Asking a Question

A good testable question should include a cause and an effect.A good testable question will focus your testing to only onefactor. For example, asking the question, "What is the effect ofsunlight on the growth of plants?" instead of "What affects thegrowth of plants?" will allow you to make predictions, create aplan, conduct a fair test, and make meaningful observations andconclusions.

Example: Testable Question

What is the effect of the application of heat on the viscosity ofa fluid?

The above question includes the cause (application of heat) andthe effect (viscosity of a liquid). These two portions of thetestable question are called variables. Variables are factors thatcan affect an event or process in some way. The cause portion ofthe testable question, representing the one thing you purposelychange, is called the Independent Variable (IV). The effectportion of the testable question, or the thing you will measure, iscalled the Dependent Variable (DV).

Sometimes placing the variables in the following manner helpsto identify each portion:

depends onDependent Variable

Independent Variable

If we were to apply this approach to the testable question abovewe might say:

the applicationThe viscosity of a fluid depends on

of heatDependent Variable

Independent Variable

Read pages 12-13 of Nelson Science and Technology SkillsHandbook to learn more about testable questions and theirindependent and dependent variables.

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Practice: Independent and Dependent Variables

Identify the independent and dependent variables in thefollowing testable questions:

1. What is the effect of the size of the tube on the flow rate of afluid?Independent VariableDependent Variable

2. What is the effect of the level of activity on a person'srespiratory rate?Independent VariableDependent Variable

3. How does the density of a substance affect the angle ofrefraction of light passing through it?Independent VariableDependent Variable

Step Two: Making a Hypothesis

A hypothesis is a suggested answer or a prediction of how onevariable affects the other. The hypothesis should predict therelationship between the independent and dependent variables.Often it follows this pattern:

NIf the

increases or decreases, then the

willincrease or decrease.

Using the example of "how heat affects viscosity":

If the amount of heat added I increases, then the viscosity j willdecrease.

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increases, then the I respiratory rate

number of bounces off the boards

decreases,

decreases.

temperature of a hockey puck

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Practice: Creating a Hypothesis

Create a hypothesis statement for the following testablequestions. (Reminder: It should include the IndependentVariable (IV) and Dependent Variable (DV) you listed above.)

1. What is the effect of the size of a tube on the flow rate of afluid?

Hypothesis:

2. What is the effect of physical conditioning on recovery rate?Hypothesis:

3. How does application of pressure affect the flow rate of afluid?Hypothesis:

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Step Three: Designing the Experiment

Ensuring a Fair Test

To conduct a fair test we must ensure that other factors thatmay affect the outcome of the experiment are controlled or keptthe same. These variables that are not changed are calledcontrolled variables. Think of the experiment to see whichsponge absorbs the most. Because a larger sponge wouldprobably absorb more liquid, the size of the sponge used is avariable we would want to control. An identically sized sample ofeach of the different types of sponges to be tested could be cutout. Then the amount of liquid each absorbed could be comparedfairly, with the results attributed to the type of sponge and notthe size of the sponge.

In the case of "the effect of application of heat on the viscosity offluid," several variables that you may wish to control or keep thesame are the

• amount of fluid

• distance the fluids have to travel

• angle of slope

For further information and examples of controls, read pages 15-16 ofNelson Science and Technology Skills Handbook.

Practice: Identifying Controlled Variables

Identify the things to control (controlled variables) wheninvestigating these testable questions:

1. How does the speed of a car affect how much gas it uses?Controlled variables:

2. How does the addition of salt affect the buoyant force exertedby water?

Controlled variables:

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3. How does water affect the size of a raisin?

Controlled variables:

Creating a Plan

The next step is to create a plan to test our hypothesis. First we

must determine what materials are needed to conduct the test.

Then we must create a plan or method. The method should be

recorded in numbered steps. To continue the concept of fair test,

the test should be done several times. This is to ensure that

results did not happen by chance or were a fluke, but are

accurate and dependable.

Learning Activity: Experimenting with Heat and Viscosity

Use the apparatus and method below to test the effect of the

application of heat on the viscosity of a liquid. Charts for

recording your results are found on pages 30-31.

Apparatus: molasses, teaspoon, cookie sheet and material to

prop it up at a slight angle, device to measure time

Method:

1. Place a teaspoon of molasses (straight from the refrigerator)on the cookie sheet.

2. Record the time it takes to flow a specific distance.

3. Heat up the teaspoon of molasses for 10 seconds in themicrowave or in a container resting in hot water for1 minute.

4. Place the teaspoon of warmed molasses on the cookie sheetand record its flow rate.

5. Heat up one teaspoon of molasses (from fridge) for 20seconds in the microwave or place in a container resting inhot water for 2 minutes.

6. Place the teaspoon of warmed molasses on the cookie sheetand record the flow rate.

7. Heat, in microwave, one teaspoon of molasses for 30 seconds

or in a container resting in hot water for 3 minutes.

8. Record flow rate.

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9. Continue tests, raising heating time by 10 seconds for eachtest up to and including 50 seconds.

10. Repeat tests.

Safety Note: This experiment should be done under thesupervision of an adult.

Step Four: Conducting the Experiment

During the experiment, it is important to follow your plan totake accurate measurements and make careful observations. Thesafety of yourself and others should always be on your mind. Toincrease the accuracy and reliability of the experiment,measurements should be repeated.

Step Five: Observing and Recording Data

Observations can be recorded in any of the following ways:• written in sentences• graphs (handwritten or computer-generated)• point-form notes• diagrams• charts

• lists

• spreadsheets

Using page 63 of Nelson Science and Technology SkillsHandbook as a reference, identify the components of thefollowing data table using the terms provided on the followingpage.

(1) Effect of Sunlight on Plant Growth(3)

(2)

Plant

Plant 1 - In Sunlight

Plant 2 - In PartialSunlight

Growth After1 Week (cm)

5

3

1Plant 3 - In Shade

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ModuIe I Lesson 3

Terms: dependent variable, unit of measurement, independentvariable, title

1.

2.

3.

4.

When you have recorded your observations, you might observepatterns and/or discrepancies in your data. These may berecorded in your observations. It is at this time that you mayalso identify possible sources of error. For example, one plantthat was in sunlight may have been exposed to spider mites ordisease, resulting in poor growth.

Recording Results

Record the test results from your experiment on the effect ofheat on the viscosity of a fluid.

Test #1

Time heated

I Length of time to

Ranking (1 is thetravel 25 cm

slowest and mostviscous substance)

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Test #2

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Time heated

0 (right fromfridge)

Length of time totravel25cm

-

-,------Ranking (fis the

I

-slowest -and most-viscous substance)

Record any possible sources of error that may have affected theoutcome of your tests.

Step Six: Organizing and Analyzing Results

If appropriate, data can be placed on a graph to better analyzethe results of your experiments. (Refer to page 64-65 of NelsonScience and Technology Skills Handbook for instructions oncreating graphs.)

Your conclusion should explain the cause and effectrelationship between the independent variable and thedependent variable. For example: In our experiment, allvariables, other than the amount of sunlight, were kept constant.The geranium plants that received additional sunlight did growmore than the plants that were only given limited amounts ofsunlight. In the 32 days that we ran the experiment, the plants

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that received an additional 10 hours of sunlight a day grew anaverage of3 cm, while the plants that received only limitedsunlight grew an average of 1 cm. Our results support ourpredictionlhypothesis.

Conclusion

Record your conclusions for your application of the heat/viscosityexperiment:

Maybe you noted in your sources of error that the molasses didnot flow in a straight line, but spread. In your Reflections onthe Process you may want to suggest ways to improve thetesting of the flow rate. You may want to suggest using achannel made of a cross section of tubing or large straw so thatthe molasses does not have the opportunity to spread but onlyflow down in the narrow channel.

Implications and Applications for Daily Use deals with howthis concept can be applied to other instances or events.Knowledge about heat and its effects on the flow rate andviscosity of a liquid may help in deciding what type of engine oilto use in different seasons, for example. You may wish to useless viscous oil in wintertime because the temperatures willcause viscosity to rise and thereby strain the engine.

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Step Seven: Communicating Results

It is important to communicate results and share with others.This can be done in a variety of ways. Lab Report templateshave been provided for you to use for experiments throughoutthe course.

Questions: Thinking about Scientific Inquiry

Complete the sentences with the choices below (one term is usedtwice).

independent variable

hypothesis

temperaturedependent variable

fair test

pressure appliedcontrolled variable

flow rate/variable

conclusiontestable question

observations

tube diameter

1. is a factor that can affect anevent or process in some way.

2. A prediction of how one variable affects the other is calleda(n)

3. The part of the experiment that we can change ormanipulate is called the

4. is a factor that can be affectedbecause of a change to other variables.

5. is determined by calculating thetime it takes a fluid to flow a certain distance.

6. can be recorded as writtensentences, graphs, point form notes, diagrams, charts, lists,and/or spreadsheets.

7. To conduct a

the investigatormust ensure that other factors that may affect the outcomeof the experiment are controlled or kept the same.

8. includes a cause and effectrelationship to investigate and focuses your testing to onlyone factor or variable.

9. An explanation of the cause and effect relationship betweenthe independent variable and the dependent variable isincluded in the

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10. Variables that are not changed are called

11. The length of time it takes an ice cube to melt would be anexample of a(n)

12. Three factors that affect the flow rate of a fluid are

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