Scientific Investigations

Scientific Investigations

Middle School

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Learning Objectives

• Tell the difference between observations, inferences, and a hypothesis.

• Describe qualitative and quantitative data used in scientific investigations.

• Find the different variables and constants in an experiment.

• Explain the difference between a scientific theory and a scientific law.

• Use graphs and tables to analyze data and make conclusions.

Key Vocabulary

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Hypothesis

An educated guess or a testable prediction, often structured as an "If, Then" statement.

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Qualitative Data

Information that describes qualities or characteristics, observed using the five senses, such as color or texture.

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Quantitative Data

Information that involves a measured quantity or amount, always represented by numbers, like length or mass.

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Independent Variable

The single factor that a scientist intentionally changes in an experiment to observe its effect.

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Dependent Variable

The factor that is measured or observed as the result of changes to the independent variable.

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Constants

All the factors and conditions that are intentionally kept the same throughout all parts of an experiment.

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Observation vs. Inference

Observation

• ​It is the process of gathering information using your five senses.

• ​​This focuses on exactly what you can see, hear, touch, smell, or taste.

• ​For example, you might observe that the plant's leaves are brown and dry.

Inference

• ​This is an explanation or conclusion that is based on your observations.

• ​​You use your previous knowledge and experiences to make a logical guess.

• ​For example, you might infer that the plant needs to be watered.

Multiple Choice

A student sees a classmate sniffing the air and says, 'It smells like cookies are baking, so the cafeteria must be making them for lunch.' Which part of this statement is the observation?

• The cookies will be delicious.

• It smells like cookies are baking.

• The cafeteria is making cookies for lunch.

• The student is hungry.

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Qualitative vs. Quantitative Data

Qualitative Data

• ​Qualitative observations describe the qualities or characteristics of something using your five senses.

• ​​These observations are described with words and do not involve numbers or measurements.

• ​For example, observing that tomatoes are red is a qualitative observation.

Quantitative Data

• ​Quantitative observations describe the amount of something and are always expressed as a number.

• ​​These observations are made using tools to measure a specific quantity.

• ​For instance, stating that there are seven apples is a quantitative observation.

Multiple Choice

Which of the following is a quantitative observation?

• The slug was slimy.

• The milk smells sour.

• The mass of the beaker was 122 g.

• The forest floor is a healthy green color.

Hypothesis, Theory, and Law

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Hypothesis

• An educated guess or prediction for a single, specific event.

• It is based on your initial observations before an experiment.

• It can be tested by a single experiment.

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Scientific Theory

• A detailed explanation for why something in nature happens.

• It is based on many hypotheses that have been proven correct.

• It is verified many times and is widely accepted by scientists.

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Scientific Law

• A statement of fact that describes a pattern in nature.

• It is considered to be true and universal in specific conditions.

• This describes what happens, but it does not explain why.

Multiple Choice

Which statement best describes a Scientific Law?

• A statement of fact that describes what happens and is generally accepted as true and universal.

• An explanation of why something happens, based on proven hypotheses.

• An educated guess for a single event that can be tested by one scientist.

• An explanation that has not yet been proven or tested.

Designing a Fair Test

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Independent Variable

• ​This is the one variable that you will intentionally change or test.

• ​​It is the 'cause' in a cause-and-effect relationship in an experiment.

• ​For example, using different types of paper to build an airplane.

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Dependent Variable

• ​This is the variable that you will measure or observe for results.

• ​​It is the 'effect' or the data that you will be collecting.

• ​For example, measuring the distance the paper airplane flew through the air.

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Constants

• ​These are all the factors you must keep the same during testing.

• ​​Keeping variables constant ensures that the results of the test are fair.

• ​For example, the paper size and airplane design must not be changed.

Multiple Choice

A student investigates which paper creates the farthest-flying airplane. She uses different paper types but keeps the plane design and size the same for every trial. What is the independent variable in this experiment?

• The person throwing the plane.

• The distance the plane flew.

• The paper type.

• The paper size and design.

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Graphing and Interpreting Data

• Graphs help you visualize relationships between variables in an experiment.

• The independent variable (IV) is always plotted on the horizontal x-axis.

• The dependent variable (DV), your collected data, goes on the vertical y-axis.

• Use bar graphs when the independent variable is a category, not a number.

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Multiple Choice

A scientist is graphing the results of an experiment that tested the 'Effect of earthworms on plant growth.' Which variables should be plotted on the X-axis and Y-axis?

• X-axis: Earthworms, Y-axis: Plant growth

• X-axis: Type of plant, Y-axis: Height of pot

• X-axis: Earthworms, Y-axis: Amount of water

• X-axis: Plant growth, Y-axis: Earthworms

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Clearing Up Common Misconceptions

Misconception	Correction
An observation and an inference are the same thing.	Observation uses senses. Inference is a conclusion from observations.
A hypothesis is just a random guess.	A hypothesis is an educated, testable guess based on prior knowledge.
Scientific theories are unreliable because they are "just theories."	A theory is a well-tested explanation supported by evidence.
Any question you can think of is a good scientific question.	A good scientific question must be testable and measurable.

Multiple Choice

A scientist studies how the amount of fertilizer affects the height of tomato plants. What are the dependent and independent variables in this investigation?

• IV: Type of plant, DV: Amount of fertilizer

• IV: Amount of water, DV: Plant height

• IV: Plant height, DV: Amount of fertilizer

• IV: Amount of fertilizer, DV: Plant height

Multiple Choice

A report states, 'The solution turned a vibrant blue color and felt warm to the touch, while its volume was measured to be 50 mL.' How can the data in this statement be categorized?

• The color is quantitative; the feel and volume are qualitative.

• Both observations are qualitative.

• Both observations are quantitative.

• The color and feel are qualitative; the volume is quantitative.

Multiple Choice

A student hypothesizes, 'If a plant is put in a sunny window, then it will grow taller than a plant in a dark closet.' After a month, the student observes the plant in the window is taller. What is a valid conclusion and why?

• The hypothesis is rejected because one experiment is not enough to form a theory.

• No conclusion can be drawn because the student did not measure the water.

• The data supports the hypothesis, suggesting a link between sunlight and growth, assuming other variables like water were controlled.

• The hypothesis is proven true because the plant in the window grew taller.

Multiple Choice

A student asks, 'Do roses smell better than tulips?' Why is this a poor scientific question and how could it be improved?

• It is a good question because it is about nature.

• It is a poor question because it is too specific. It should be broadened to ask about all flowers.

• It is a poor question because 'smelling better' is an opinion. It could be improved by testing if bees are more attracted to the scent of roses or tulips.

• It is a good question because it is testable with a poll.

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Summary

• Observations are gathered with the five senses; inferences are conclusions from observations.

• Qualitative data is descriptive, while quantitative data is numerical.

• A fair test changes the independent variable to measure the effect on the dependent variable.

• A hypothesis is a specific, testable prediction for an experiment.

• A scientific theory explains why something happens; a scientific law describes what happens.

• The independent variable is on the x-axis, and the dependent variable is on the y-axis.

Poll

On a scale of 1-4, how confident are you in designing your own fair scientific test?

• 1

• 2

• 3

• 4