Why do scientists use controlled experiments instead of only observing?

Why do scientists use controlled experiments instead of only observing?

• A. To observe everything that happens in a system
• B. To establish cause-and-effect relationships by controlling variables
• C. To prove that hypotheses are always true
• D. To collect data without making predictions

Answer: (B)

Controlled experiments let scientists test whether a specific factor actually causes a change by isolating that factor and keeping everything else the same. For example, to see if fertilizer makes plants grow taller, you give different amounts of fertilizer to otherwise identical plants while keeping light, water, soil, and pot the same. If the plants with more fertilizer grow taller, you can infer that the fertilizer contributes to growth under those conditions. Simply watching what happens can't show cause and effect because many factors could change outcomes at once, so you can't know which one is responsible. Experiments also let other scientists repeat the test and see if results are consistent. The other options don’t describe how experiments reveal cause and effect; observing everything lacks control, saying hypotheses are always true isn’t accurate, and collecting data without predictions isn’t how scientists test ideas.

Controlled experiments let scientists test whether a specific factor actually causes a change by isolating that factor and keeping everything else the same. For example, to see if fertilizer makes plants grow taller, you give different amounts of fertilizer to otherwise identical plants while keeping light, water, soil, and pot the same. If the plants with more fertilizer grow taller, you can infer that the fertilizer contributes to growth under those conditions. Simply watching what happens can't show cause and effect because many factors could change outcomes at once, so you can't know which one is responsible. Experiments also let other scientists repeat the test and see if results are consistent. The other options don’t describe how experiments reveal cause and effect; observing everything lacks control, saying hypotheses are always true isn’t accurate, and collecting data without predictions isn’t how scientists test ideas.