Experimental Design
📋 What it is
A fair test changes only ONE variable and keeps everything else the same (the control).
🗣️ Coach says
To know what caused a result, change just ONE thing at a time. If you change the water AND the sunlight, you’ll never know which mattered. The stuff you keep the same for comparison is the “control”. One variable — that’s the golden rule.
🧠 Memory hook
Change ONE thing, keep the rest the same. That one thing is the variable.
😂 Giggle
What did the scientist say when they found two isotopes of helium?
HeHe!
😲 Whoa!
A “controlled experiment” is the gold standard of science — it’s the only way to prove one thing CAUSED another rather than just happened alongside it.
✅ Quick check: You give a plant more water AND more sun; it grows taller. What caused it?
Say your answer out loud first — then reveal.
You can’t tell — two variables changed, so the fair-test rule was broken; isolate one to know the cause.
Changing more than one variable makes the cause impossible to pin down.
🪄 Trick question: Is “I tested it once and it worked” enough proof?
Careful — think it through, then reveal.
No — one trial could be luck; a fair test repeats to be sure the result is real, not a fluke.
Repeating trials guards against chance results.
🧪 Try it! (2 minutes)
Design a fair test for “does warm water dissolve sugar faster?” — name the ONE variable you change and 3 things you keep the same.