Nature of Science and Experimental Design

Scientific Inquiry is the way scientists learn about the world.

It means asking questions, looking closely, testing ideas, and sharing what we learn.

You can be a scientist too. When you wonder, "What will happen if I put a plant in the sun?" or "Which toy car rolls farther?" you are starting scientific inquiry.

Scientific inquiry helps us answer questions about nature in a careful way. We do not just guess. We observe, test, and check.

1. Ask a testable question

A testable question is a question you can answer by observing, measuring, or doing a simple test.

• Testable: "Do plants grow better in sunlight or in shade?"
• Testable: "Which paper towel soaks up more water?"
• Not testable: "Is summer the best season?"
• Not testable: "Are puppies the cutest animals?"

A good scientific question is about something you can see, count, compare, or measure.

2. Learn a little first

Before testing, scientists often do background research. That means they learn a little more first.

For a 2nd grader, this can mean:

• Reading a book
• Looking at pictures
• Asking a teacher
• Watching nature carefully

If you want to know whether worms like wet soil, you might first learn that worms live in dirt and need moisture.

3. Make a prediction

A prediction is what you think will happen.

You can say, "I think the plant in the sun will grow taller."

A prediction is not a random guess. It is an idea based on what you already know.

4. Plan a fair test

A fair test means you change one thing and keep the other things the same.

For example, if you are testing sunlight and plants, the plants should have:

• The same kind of plant
• The same size pot
• The same amount of water
• The same kind of soil

The one thing you change is the amount of sunlight.

This helps you know what caused the change.

5. Observe and collect data

Observe means to look carefully using your senses.

Data is the information you collect. Data can be:

• Words: "The leaf looks green."
• Numbers: "The plant is 8 inches tall."
• Counts: "3 seeds sprouted."

Scientists write down what they notice. This helps them remember and compare.

You can make a simple chart like this:

Day 1: Plant A = 4 inches, Plant B = 4 inches

Day 5: Plant A = 7 inches, Plant B = 5 inches

6. Look at the data

After the test, scientists look at the data and think, "What does this tell me?"

If one plant grew taller, the data helps show that.

Sometimes the answer is clear. Sometimes scientists need more tests.

7. Make a conclusion

A conclusion tells what you learned from your test.

For example: "The plant in sunlight grew taller than the plant in shade."

A conclusion should match the data you collected.

8. Share findings

Scientists tell others what they did and what they learned.

You can share by:

• Talking to the class
• Drawing a picture
• Making a chart
• Writing a few sentences

Sharing helps other people learn too.

Scientific claims and non-scientific claims

A scientific claim is an idea that can be tested with observations or experiments.

A non-scientific claim is an idea that cannot be tested in that way.

• Scientific claim: "Bean plants grow faster with more sunlight."
• Non-scientific claim: "Bean plants are happier near a red wall."

The first claim can be tested by growing plants and measuring them.

The second claim uses the word "happier," which is hard to measure in a simple science test.

Worked Example 1: Which object sinks?

Question: Which will sink in water: a rock or a leaf?

Prediction: I think the rock will sink and the leaf will float.

Fair test: Put both objects in the same bowl of water.

Observe: The rock goes to the bottom. The leaf stays on top.

Conclusion: The rock sank, and the leaf floated.

This is scientific inquiry because we asked a testable question and checked it by observing.

Worked Example 2: Which paper towel soaks up more water?

Question: Does Paper Towel A soak up more water than Paper Towel B?

Prediction: I think Paper Towel A will soak up more water.

Fair test:

• Use the same size pieces
• Use the same amount of water
• Test both towels the same way

Data:

• Paper Towel A soaked up 6 spoonfuls.
• Paper Towel B soaked up 4 spoonfuls.

We can compare the numbers:

$$6 > 4$$

Conclusion: Paper Towel A soaked up more water.

Worked Example 3: Do plants need sunlight?

Question: Do plants grow better in sunlight than in shade?

Background research: Plants need light to grow.

Prediction: I think the plant in sunlight will grow taller.

Fair test:

• Use 2 of the same kind of plant
• Give both the same water
• Use the same soil and pot size
• Change only the sunlight

Data:

• Sunlight plant: 9 inches
• Shade plant: 6 inches

The difference is:

$$9 - 6 = 3$$

Conclusion: The plant in sunlight grew 3 inches taller, so sunlight helped it grow more.

Worked Example 4: Is this claim scientific?

Claim 1: "Red flowers get more bees than yellow flowers."

This is a scientific claim because we can count bees on red flowers and yellow flowers.

Claim 2: "Red flowers are prettier than yellow flowers."

This is a non-scientific claim because "prettier" is a personal opinion.

How to remember scientific inquiry

1. Ask a question
2. Learn a little
3. Make a prediction
4. Do a fair test
5. Observe and collect data
6. Make a conclusion
7. Share what you learned

Helpful science words

• Observe: look carefully
• Prediction: what you think will happen
• Data: information you collect
• Fair test: change one thing and keep the rest the same
• Conclusion: what you learned
• Claim: an idea or statement

Let's practice thinking like scientists

If you ask, "Which melts faster, ice in the sun or ice in the shade?" that is a testable question.

You could predict, test it, and time what happens.

If you ask, "Is ice cream the most amazing food ever?" that is not a scientific question because it is based on opinion.

Summary

Scientific inquiry is a careful way to learn about the world.

We ask testable questions, make predictions, do fair tests, collect data, and make conclusions.

Scientific claims can be tested with observations or experiments. Non-scientific claims are based on opinion or ideas that cannot be tested easily.

When you wonder, test, and share, you are doing science.

Qualitative and Quantitative Data

When scientists study something, they observe it carefully. They look, listen, touch, and measure. Then they write down what they learn. The information they collect is called data.

There are two main kinds of data we can collect in science:

• Qualitative data
• Quantitative data

Both kinds of data are important. They help us learn about plants, animals, weather, rocks, water, and many other things in nature.

What is qualitative data?

Qualitative data tells us about qualities, or what something is like. It uses words, not numbers.

Qualitative data can describe:

• color
• shape
• texture
• sound
• smell
• how something looks or feels

Examples of qualitative data:

• The flower is yellow.
• The rock feels rough.
• The water looks clear.
• The bird sounds loud.

These are all describing words. They tell us what we notice.

What is quantitative data?

Quantitative data tells us about amounts. It uses numbers.

Quantitative data can tell us:

• how many
• how much
• how long
• how tall
• how heavy

Examples of quantitative data:

• There are 5 worms.
• The plant is 8 inches tall.
• We saw 3 clouds.
• The class has 20 seeds.

These are all number facts. They tell us an amount.

An easy way to remember

• Qualitative = quality = words
• Quantitative = quantity = numbers

If your observation uses words like green, smooth, loud, sweet, soft, it is probably qualitative.

If your observation uses numbers like 2, 7, 10 inches, it is probably quantitative.

Why do scientists use both kinds?

Scientists do better work when they collect both kinds of data. Words help describe what something is like. Numbers help show exact amounts.

For example, if we study a leaf, we might write:

• Qualitative: The leaf is green and smooth.
• Quantitative: The leaf is 4 inches long.

Now we know more because we used words and numbers.

Worked Example 1: Looking at a flower

A student observes a flower and writes these notes:

• The flower is pink.
• The flower has 6 petals.

Let us sort the data.

• The flower is pink → qualitative data, because it uses words to describe color.
• The flower has 6 petals → quantitative data, because it uses a number.

Worked Example 2: Watching the weather

A class looks outside and writes:

• The sky is cloudy.
• We see 4 puddles.
• The wind feels cool.

Now we sort them.

• The sky is cloudy → qualitative
• We see 4 puddles → quantitative
• The wind feels cool → qualitative

In this example, the class used both kinds of data.

Worked Example 3: Measuring a plant

A plant investigation gives these notes:

• The plant is 9 inches tall.
• The leaves are bright green.
• The plant has 3 flowers.

Let us think carefully.

• 9 inches tall → quantitative, because it tells a measured amount.
• bright green → qualitative, because it tells what the leaves look like.
• 3 flowers → quantitative, because it tells how many.

We can even write the number sentence for the flowers:

Number of flowers = \(3\)

Worked Example 4: Studying rocks

A group studies one rock and writes:

• The rock is gray.
• The rock feels rough.
• The rock is 2 inches long.
• There are 7 small spots on the rock.

Here is how we sort the data.

• gray → qualitative
• rough → qualitative
• 2 inches long → quantitative
• 7 small spots → quantitative

This example is helpful because one object can have many kinds of data.

How to collect data in science

1. Look at the object or event carefully.
2. Write down what you notice with words.
3. Count or measure if you can.
4. Keep your notes neat and clear.

For example, if you observe a bug, you might write:

• It is black. (qualitative)
• It has 6 legs. (quantitative)

Words that can help with qualitative data

• red, blue, green, yellow
• smooth, rough, soft, hard
• big, tiny
• wet, dry
• loud, quiet

Words and ideas that can help with quantitative data

• how many
• how tall
• how long
• how much
• counting and measuring

Let us compare the two kinds of data

• Qualitative data tells what it is like.
• Quantitative data tells how many or how much.

Here are two observations about the same apple:

• The apple is red and shiny. (qualitative)
• The apple has 1 stem. (quantitative)

Both observations are useful.

Be careful

Sometimes a describing word like big can tell us something, but it is not exact. That means it is usually qualitative.

If we say something is 10 inches long, that is exact and uses a number. That means it is quantitative.

Scientists like to be careful observers. They try to collect good qualitative data and good quantitative data.

Quick practice

• The puddle is muddy. → qualitative
• There are 8 ducks in the pond. → quantitative
• The shell feels smooth. → qualitative
• The caterpillar is 2 inches long. → quantitative

Summary

Data is the information we collect in science. Qualitative data uses words to describe what something is like. Quantitative data uses numbers to tell how many or how much.

When you do a science investigation, try to collect both kinds of data. That helps you become a careful and smart scientist.

Drawing Evidence-Based Conclusions means using what you observed to decide what is most likely true.

In science, we do not just guess. We look at the evidence. Evidence is the information we get from an experiment, a test, or careful observations.

A conclusion is what we decide after we look at the evidence. A good conclusion tells what happened and how the evidence helps us know.

Scientists often begin with a hypothesis. A hypothesis is a smart idea or prediction, like, “I think a plant in sunlight will grow taller than a plant in a dark place.”

After the experiment, we ask an important question: Does the evidence support the hypothesis or not?

Sometimes the evidence supports the hypothesis. Sometimes it does not. Both are okay in science. What matters most is being honest and using the evidence.

How to Draw an Evidence-Based Conclusion

1. Look at the question. What were you trying to find out?
2. Look at the hypothesis. What did you think would happen?
3. Look at the evidence. What did you observe, measure, or count?
4. Decide what the evidence shows. Did the results match the hypothesis or not?
5. Explain your thinking. Tell which evidence helped you decide.

Helpful sentence starters:

• “My evidence shows that...”
• “I observed that...”
• “The data tells me that...”
• “This supports my hypothesis because...”
• “This does not support my hypothesis because...”

What counts as evidence?

• What you saw
• What you heard
• What you measured
• What you counted
• What happened each time you tested

What does not count as good evidence?

• A wild guess
• What you hoped would happen
• What a friend said without testing
• An answer with no observations to support it

Remember: A conclusion is stronger when it uses real facts from the experiment.

Worked Example 1: Which toy car went farther?

Question: Does a toy car go farther on a smooth floor or on carpet?

Hypothesis: I think the toy car will go farther on the smooth floor.

Evidence:

• On the smooth floor, the car went 8 steps.
• On carpet, the car went 3 steps.

Conclusion: The evidence supports the hypothesis. The car went farther on the smooth floor because it traveled 8 steps, but on carpet it only traveled 3 steps.

Why is this a good conclusion? It tells what happened and uses the numbers from the test as evidence.

Worked Example 2: Do bigger seeds sprout first?

Question: Do bigger seeds sprout faster than smaller seeds?

Hypothesis: I think bigger seeds will sprout first.

Evidence:

• Big seed A sprouted in 5 days.
• Big seed B sprouted in 6 days.
• Small seed A sprouted in 4 days.
• Small seed B sprouted in 5 days.

Conclusion: The evidence does not support the hypothesis. The smaller seeds sprouted as fast as or faster than the bigger seeds. One small seed sprouted in 4 days, which was sooner than both big seeds.

Why is this a good conclusion? It does not just say “I was wrong.” It explains what the evidence showed.

Worked Example 3: Which paper towel holds more water?

Question: Which paper towel brand holds more water?

Hypothesis: I think Brand A will hold more water.

Evidence:

• Brand A held 6 spoonfuls of water.
• Brand B held 9 spoonfuls of water.

Conclusion: The evidence does not support the hypothesis. Brand B held more water than Brand A. Brand B held 9 spoonfuls, and Brand A held 6 spoonfuls.

We can even see the difference with a subtraction sentence:

$$9 - 6 = 3$$

Brand B held 3 more spoonfuls of water.

Why is this a good conclusion? It uses measured evidence and compares the results clearly.

Worked Example 4: Do plants need sunlight to grow well?

Question: Do plants grow better with sunlight?

Hypothesis: I think plants with sunlight will grow better.

Evidence after 2 weeks:

• Plant in sunlight grew to 10 inches and had green leaves.
• Plant in a dark place grew to 4 inches and had yellow leaves.

Conclusion: The evidence supports the hypothesis. The plant in sunlight grew taller and looked healthier. It grew to 10 inches, while the plant in the dark only grew to 4 inches.

We can compare the heights:

$$10 - 4 = 6$$

The plant in sunlight grew 6 more inches.

Why is this a good conclusion? It uses more than one piece of evidence: height and leaf color.

Tips for Strong Conclusions

• Be truthful. Say what the evidence really shows.
• Use details. Include numbers, words, or observations from the experiment.
• Answer the question. Make sure your conclusion fits the question you were testing.
• Say if the hypothesis was supported or not.
• Explain why. Tell which evidence helped you decide.

Be careful of these mistakes:

• Saying what you wanted to happen instead of what really happened
• Forgetting to use evidence
• Giving a conclusion that does not answer the question
• Using only one tiny clue when there is more evidence to look at

Let's practice thinking like a scientist.

If you tested two kinds of soil and one plant grew taller in Soil 1, you should not just say, “Soil 1 is better.” A stronger conclusion is, “The plant in Soil 1 grew taller, so the evidence shows Soil 1 helped this plant grow better in this test.”

That is stronger because it tells what happened and why you think that.

A simple conclusion pattern

You can use this pattern when you write:

“My hypothesis was ________. The evidence supports / does not support my hypothesis because ________.”

Example: “My hypothesis was that the smooth floor would help the toy car go farther. The evidence supports my hypothesis because the car went 8 steps on the smooth floor and only 3 steps on the carpet.”

Summary

Drawing an evidence-based conclusion means looking at the results of an experiment and deciding what they show.

A strong conclusion uses real observations, counts, or measurements. It tells whether the evidence supports the hypothesis or does not support it.

In science, the best answers are not based on guesses. They are based on evidence.