3 Conducting and Recording Experiments

Start with a focused question

A scientific investigation begins with a focused question that can be explored by gathering evidence. An experiment is one kind of investigation: it tests how changing a condition affects what happens. Scientists do not all follow one rigid sequence of steps, but careful planning, observation, and record-keeping help make an investigation useful and understandable.

Plan a fair, repeatable test

Decide what you will do and what you will observe or measure. In a fair test, change one condition at a time and keep other important conditions the same. Write a clear, ordered procedure so another person could follow it. Include the materials, how measurements will be taken, and how many trials will be made.

For example, to compare how much water different paper towels absorb, use pieces of the same size, the same amount of water, and the same soaking time. Measure the water absorbed in the same way each time. Repeat each test, then compare the results. Repeated trials help show whether a pattern is consistent or whether one result may have been unusual.

Work safely

Plan for safety before beginning. Follow the teacher’s instructions, use only approved materials and equipment, wear any required protective gear, and do not taste or handle substances unless explicitly instructed. Stop and tell the teacher if something spills, breaks, or seems unsafe.

School investigations should be selected and supervised with students’ age and the activity’s hazards in mind.

Record observations and results

Record observations as you work rather than relying on memory afterward. A useful record includes the date, question, procedure, materials, and results. Organize results in a labeled table, include units with measurements, and use words or drawings to note details that numbers do not capture. Keep the measurement method the same across trials.

For example, a paper-towel test might record these results:

• Trial $1$: $20\ \text{mL}$ of water added; $12\ \text{mL}$ absorbed.

• Trial $2$: $20\ \text{mL}$ of water added; $11\ \text{mL}$ absorbed.

• Trial $3$: $20\ \text{mL}$ of water added; $12\ \text{mL}$ absorbed.

Labeled entries with units make evidence easier to compare and help another person understand how the results were obtained. Accurate documentation of procedures and data supports review and attempts to repeat an investigation.

Separate observations from inferences

An observation is information gathered directly with the senses or a measuring tool. A qualitative observation describes a quality, such as “the towel felt damp.” A quantitative observation gives a measurement, such as “it absorbed $12\ \text{mL}$ of water.”

An inference is an interpretation or explanation based on observations and other knowledge. For example, “the plant’s leaves drooped, and the soil felt dry” describes observations; “the plant may need water” is an inference. That inference is reasonable, but it is not directly observed, and other explanations may also be possible.

Keep observations separate from interpretations in your notes. Use evidence to explain why an inference makes sense, and make sure a conclusion matches the results while acknowledging when the evidence is limited or uncertain.

Draw evidence-based conclusions

A strong investigation is planned around a clear question, carried out safely, and described so it can be repeated. Record observations promptly and precisely, including measurements, units, and trial details. Distinguish what was directly observed from what is inferred, and base conclusions on the collected evidence.