Investigation Lab
Learn
In this lesson, you will learn how to plan and conduct a complete scientific investigation from start to finish.
What is a Scientific Investigation?
A scientific investigation is a systematic process used to answer questions about the natural world. It involves making observations, forming hypotheses, designing experiments, collecting data, and drawing conclusions.
The Scientific Method
Every investigation follows a series of steps known as the scientific method:
- Ask a Question: Identify what you want to learn. Good questions are specific and testable.
- Research: Learn what is already known about your topic.
- Form a Hypothesis: Make an educated prediction using an "If...then..." statement.
- Design an Experiment: Plan your procedure, identify variables, and determine what materials you need.
- Conduct the Experiment: Follow your procedure carefully and record observations.
- Analyze Data: Organize your results and look for patterns.
- Draw Conclusions: Determine whether your hypothesis was supported or refuted.
- Communicate Results: Share your findings with others.
Writing a Good Hypothesis
A hypothesis is a testable prediction. It should be written in "If...then...because..." format:
- If [independent variable changes in this way],
- then [dependent variable will respond in this way],
- because [scientific reasoning].
Example: "If a plant receives more sunlight, then it will grow taller, because sunlight provides energy for photosynthesis."
Designing a Fair Test
A fair test (or controlled experiment) ensures that only one variable changes at a time. Remember:
- Change only the independent variable
- Measure the dependent variable
- Keep all controlled variables the same
- Include a control group for comparison
- Use multiple trials for reliable results
Lab Safety
Before conducting any investigation, always follow safety guidelines:
- Wear appropriate safety equipment (goggles, gloves, aprons)
- Read all instructions before starting
- Handle materials carefully
- Clean up your workspace
- Report any accidents or spills immediately
Examples
Work through these examples to see how to plan and conduct investigations.
Example 1: Planning a Plant Growth Investigation
Question: How does the amount of water affect plant growth?
Hypothesis: If a plant receives more water (up to a certain point), then it will grow taller, because water is essential for transporting nutrients and maintaining cell structure.
Variables:
- Independent variable: Amount of water given daily
- Dependent variable: Plant height (in cm)
- Controlled variables: Type of plant, amount of sunlight, soil type, pot size, temperature
Procedure:
- Plant 15 identical bean seeds in identical pots with the same soil.
- Divide into 3 groups of 5 plants each.
- Group A: 10 mL water daily; Group B: 30 mL water daily; Group C: 60 mL water daily
- Place all pots in the same location with equal sunlight.
- Measure and record plant height every 3 days for 3 weeks.
Example 2: Identifying Flaws in an Experiment
Scenario: A student wants to test if temperature affects how fast sugar dissolves. She heats one cup of water to 80 degrees C and keeps another at 20 degrees C. She adds 1 tablespoon of sugar to the hot water and 2 tablespoons to the cold water, then times how long it takes to dissolve.
Problem: This is not a fair test because TWO variables changed (temperature AND amount of sugar). The results won't show the effect of temperature alone.
Correction: Use the same amount of sugar (1 tablespoon) in both cups. Only the temperature should differ.
Practice
Try these problems on your own to reinforce your learning.
1. Put the following steps of the scientific method in the correct order:
A) Analyze data B) Form a hypothesis C) Ask a question D) Conduct the experiment E) Draw conclusions F) Design an experiment
2. Rewrite this hypothesis in proper "If...then...because" format: "I think plants grow better with music."
3. A student tests how fertilizer affects plant growth. She uses 3 plants: one gets no fertilizer, one gets 5g, and one gets 10g. All plants are placed near different windows. What is wrong with this experimental design?
4. For an experiment testing whether salt affects the boiling point of water, identify:
a) The independent variable
b) The dependent variable
c) Three controlled variables
5. Why is it important to conduct multiple trials in an experiment?
6. A scientist wants to test if a new medicine reduces headaches. She gives the medicine to 50 people with headaches. 40 people report feeling better. Can she conclude the medicine works? What is missing from her experiment?
7. Write a testable question about the relationship between exercise and heart rate.
8. Design an experiment to test whether the color of light affects how well plants grow. Include:
a) Your hypothesis
b) Independent variable
c) Dependent variable
d) At least 3 controlled variables
e) A brief procedure (4-5 steps)
9. What is the purpose of a control group in an experiment?
10. A student's experiment shows results that contradict her hypothesis. What should she do next?
Check Your Understanding
Test yourself with these review questions.
1. Which of the following is the best example of a testable hypothesis?
- A) Plants like sunlight.
- B) If plants receive more sunlight, then they will grow taller.
- C) Sunlight is good for plants.
- D) Plants need sunlight to be happy.
2. In a controlled experiment, which variable does the scientist change on purpose?
- A) Dependent variable
- B) Controlled variable
- C) Independent variable
- D) Responding variable
3. What is the main purpose of keeping controlled variables constant?
- A) To make the experiment easier to conduct
- B) To ensure only the independent variable affects the results
- C) To reduce the number of materials needed
- D) To make the experiment faster
Next Steps
- Practice writing hypotheses for everyday observations
- Review the scientific method steps until you can recite them from memory
- Think about how you could design a fair test for questions that interest you
- Move on to the next lesson: Data and Graphs