LyfeLabz | How to Conduct Experiments

SEP 1 Asking questions and defining problems: ask questions that arise from careful observation of phenomena and that can be investigated through a controlled experiment.

SEP 3 Planning and carrying out investigations: identify independent and dependent variables and the controls that must be kept constant for a fair test.

SEP 4 Analyzing and interpreting data: distinguish between qualitative and quantitative observations, and between observations and the inferences drawn from them.

Learning Goals

What You'll Be Able to Do

By the end of this lesson, you will be able to:

❓

Write a testable hypothesis that explains the cause-and-effect relationship between variables, using the if - then - because frame.

SEP 1

🧪

Identify the independent variable, dependent variable, and control variables in any experiment.

SEP 3

📏

Classify observations as quantitative (numbers and measurements) or qualitative (senses and descriptions).

SEP 4

🕵️

Explain the difference between an observation and an inference, and draw reasonable inferences from evidence.

SEP 4

Engage · Mystery

Three Everyday Mysteries

Science doesn't start in a lab. It starts the moment you notice something and ask, "Wait... why does that happen?" Click each card and see what questions pop into your head.

🥤

The Eruption

You drop a Mentos candy into a bottle of soda. In one second, foam blasts out of the bottle like a geyser - but only with some sodas, and not others.

What would make the eruption bigger or smaller? How could you find out?

Click to look closer

🌱

The Thirsty Plant

You have three identical plants. You water one a little, one a medium amount, and one a lot. After two weeks, they look completely different.

Which amount of water will cause the plant to grow the healthiest? How would you prove it?

Click to look closer

🌫️

The Wet Grass

You step outside in the morning and the grass is soaked - but you never heard rain overnight, and the sidewalk is dry.

What happened while you were asleep? What's your best explanation?

Click to look closer

💡 Notice something? Each mystery began the same way: you observed something, and a question appeared. Scientific inquiry always starts with a question, driven by curiosity or a desire to solve a problem.

🤔 But a question alone isn't an answer. To get an answer you can trust, you need a plan - and that plan is called an experiment.

The mission: By the end of this lesson, you'll be able to take any "why does that happen?" question and design a fair experiment to answer it. Step one: make an educated guess.

Explore · The Educated Guess

What Is a Hypothesis?

Before scientists test anything, they predict what will happen and why. That prediction has a name.

The key idea

A hypothesis is an educated guess that explains an observation based on your prior knowledge. A good hypothesis is testable and explains the cause-and-effect relationship between variables.

✅ Testable: "Plants given more sunlight will grow taller" - you can actually run this experiment and measure the result.

❌ Not testable: "Plants are happier in the sun" - how would you ever measure a plant's happiness?

🥤

Back to the eruption: Mentos dropped into which soda will cause the biggest foaming eruption? Make a prediction to unlock the Hypothesis Builder.

🧪 The Hypothesis Builder

A strong hypothesis has three parts. Use the drop-downs to build one for the Mentos experiment, then check it.

1If - the change you will make (the cause).

2Then - the result you predict (the effect).

3Because - your reasoning, based on what you already know.

If Mentos are dropped into , then it will cause , because .

A hypothesis points at a cause and an effect. The thing you change... the thing that responds... scientists have exact names for those. Time to meet the variables.

Explain · The Variables

What Are the Variables?

Every fair experiment has three kinds of factors. Follow the color coding through the rest of the lesson: teal is what you change, orange is what responds, and green is what stays the same.

You change it

🎛️

Independent Variable

The factor in the experiment that you manipulate or change. In the plant experiment: the amount of water.

The Cause

➜

It responds

📈

Dependent Variable

The factor in the experiment that responds to the change. In the plant experiment: how healthy each plant grows.

The Effect

➕

You keep it the same

🔒

Control Variables

The other factors kept constant to ensure any change measured was due to the independent variable. Same pot, same soil, same sunlight.

The Fair Test

🤔

Think about it: In the plant experiment, why bother keeping the sunlight the same for all three plants? Make a prediction to unlock the sorting challenge.

Here's why it matters

If one plant got more sunlight and more water, you could never tell which one caused it to grow taller. Keeping everything else constant means the independent variable is the only possible cause of the change you measure. That's what makes a test fair.

🌱 Variable Sorter: The Plant Experiment

A student waters three identical plants with different amounts of water and measures their height after two weeks. Sort each factor into its role.

💧The amount of water each plant gets

📏The height of each plant after two weeks

☀️The amount of sunlight each plant receives

🪴The type of soil and size of pot

🏆 All sorted! You just identified every variable like a scientist planning a fair test.

Quick Recall

Just a quick brain check before we move on. Not graded.

In the Mentos experiment, you drop the same candy into three different sodas and measure how high each eruption goes. What is the independent variable?

The height of the eruption The type of soda The number of Mentos dropped in

Question → hypothesis → fair test. Now the experiment is running. But what exactly do you write down while it happens? Time to talk about observations.

Explain · Collecting Evidence

Two Types of Observations

Scientists collect evidence in two flavors: with instruments and numbers, or with their senses and descriptions. Both are useful - but they're not the same.

📏 Quantitative observations involve precise measurements and numerical quantities. Objective measures: length, height, temperature, time. "The eruption reached 2.3 meters."

👃 Qualitative observations involve using sensory information to describe something's qualities. Subjective measures: colors, textures, smells, tastes. "The foam was white and smelled sweet."

Memory trick

Quantitative sounds like quantity - a number you can count or measure. Qualitative sounds like quality - a description from your senses.

🔬 Observation Sorter

A scientist recorded these notes during the plant experiment. Sort each one: quantitative (numbers) or qualitative (senses)?

🌡️"The greenhouse temperature was 24°C."

🍃"The leaves on plant B feel waxy and look dark green."

⏱️"Plant C grew 4 centimeters in 14 days."

👃"The soil in pot A smells damp and earthy."

🏆 All sorted! Numbers and measurements are quantitative; sensory descriptions are qualitative.

Observations are what you actually see, measure, hear, or smell. But scientists do one more thing with their evidence: they figure out what it means. That step has its own name too.

Elaborate · Reading the Clues

What Is an Inference?

Detectives don't see the crime - they see the clues and work out what happened. Scientists do exactly the same thing with observations.

The key idea

An inference is a conclusion that you draw about something based on your observations. You didn't see it happen - your brain filled in the most likely explanation.

🧥

Try it: You observe someone wearing a raincoat and carrying an umbrella. What can you infer?

The reasonable inference

You can infer that they think it is going to rain. You never observed rain - you observed a raincoat and umbrella, and your brain connected the clues to the most likely explanation. That's an inference: a conclusion built from observations.

🌫️

One more - remember the mystery from the start? You step outside in the morning and observe that the grass is wet. What can you infer?

The reasonable inference

You can infer that it rained overnight or dew formed on the grass. Notice that the dry sidewalk is also an observation - it's a clue that points toward dew rather than rain. Better observations lead to better inferences.

👀 Observation: information you collect directly with senses or instruments. "The grass is wet."

🧠 Inference: the conclusion your brain draws from those observations. "It probably rained or dew formed."

Quick Recall

One more brain check. Not graded.

A student writes in her lab notebook: "The Mentos eruption was probably bigger in diet soda because diet soda holds more dissolved gas." Is that an observation or an inference?

An observation - she wrote it down during the experiment An inference - it's a conclusion explaining what she observed A control variable - it stayed the same

Back to the Eruption

You started with a foamy mystery. Now you have the full scientist's toolkit to solve it - or any mystery.

Start With a Question

Scientific inquiry begins with curiosity.

"Which soda makes the biggest eruption?" Then turn the question into a hypothesis: a testable, educated guess that names a cause and an effect.

Design a Fair Test

Change one thing, measure one thing, lock everything else.

Every fair experiment uses the same three roles:

Independent · change it Dependent · measure it Controls · keep them same

Collect and Conclude

Observe carefully, then infer.

Record quantitative observations (numbers) and qualitative observations (senses), then draw an inference: the conclusion your evidence supports.

Evaluate · Lesson Summary

Key Vocabulary & Learning Goals

Everything from this lesson in one place: the words to know and the goals you worked toward.

Term	Student-Friendly Definition
Hypothesis	An educated guess that explains an observation based on prior knowledge. A good one is testable and explains the cause-and-effect relationship between variables.
Independent variable	The factor in the experiment that you manipulate or change.
Dependent variable	The factor in the experiment that responds to the change - the thing you measure.
Control variables	The other factors kept constant to ensure any change measured was due to the independent variable.
Quantitative observation	An observation using precise measurements and numerical quantities: length, height, temperature, time.
Qualitative observation	An observation using sensory information to describe qualities: colors, textures, smells, tastes.
Inference	A conclusion you draw about something based on your observations.

Learning Goals	How You Showed It
Write a testable hypothesis using the if - then - because frame (SEP 1).	You built a complete hypothesis for the Mentos experiment and checked whether it was testable and explained a cause-and-effect relationship.
Identify independent, dependent, and control variables (SEP 3).	You sorted every factor in the plant experiment into its correct role and explained why control variables make a test fair.
Classify observations and draw inferences (SEP 4).	You sorted lab-notebook entries into quantitative and qualitative, and drew reasonable inferences from the raincoat and wet-grass clues.

Essential question: How do scientists turn a curious question into an answer they can trust? If you can answer that using the words hypothesis, independent variable, dependent variable, control variables, observation, and inference, you own this lesson.

Quiz

Check Your Understanding

Five questions covering everything you discovered, including a brand-new experiment for you to analyze. Answer every question, then submit.

Your score will not be sent Your score will be sent to your teacher

0 / 5 selected

🔍 The Mystery You Came In With You started this lesson with one question: "How do scientists turn a curious question into an answer they can trust?" If you can name the variables, write a hypothesis, and tell observations from inferences, you've earned the toolkit.

How to Conduct Experiments

What You'll Be Able to Do

Words You'll Meet

Three Everyday Mysteries

What Is a Hypothesis?

What Are the Variables?

Two Types of Observations

What Is an Inference?

Back to the Eruption

Key Vocabulary & Learning Goals

Check Your Understanding

More Learning