Fair, Repeated Trials

OKAY, BUT… HOW? · A closer look

Question: How can you tell whether a changed release point helps?

You’ll be able to: Plan a comparable repeated trial, record every outcome and identify a remaining limitation.

Decide your question before releasing the marble: does changing the release mark affect whether it stays in the cup? Name what you change and what you observe.

For this comparison, keep the marble, track, cup and let-go method as steady as you can. Repeat both release settings and record every result, including misses. If the track shifts, record that too: an uncontrolled change can confuse the comparison.

Repeated trials reveal variation. They do not guarantee a universal rule or remove every error. A consistently crooked ruler can give consistently wrong measurements. Changing one factor is useful here; more complex experiments can deliberately study several factors together.

Diagram in words: Below Quinn’s branded header is a trial plan. Only the release mark changes between A and B; marble, track, cup and release method stay comparable. A blank table has trial, release mark and stayed or missed columns, followed by a reminder to record changes.

Open the full-resolution diagram

Try the idea

A release gives one catch. The next trial misses after the track shifts. Should you delete the miss?

Answer: No. Record the miss and the shift. It is useful information about the conditions. Compare repeated trials of both settings, and do not present a shifted track as an unchanged comparison.

A little further, if you want

Optional observation: use an existing low, stable cardboard track, books, tape, one marble and a catching tray. No tools, tall runs, stairs or roads. Keep the marble away from young children and pets; never put it in your mouth. Diagram reasoning needs no materials. No outcome is promised.

See it in action

One More Take — Quinn repeats low and high releases, then checks the changed lower-shelf arrangement before filming.

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Sources

• NIST: What is experimental design? — Planning factors and responses.
• NIST: Variability — Variation in repeated measurements.
• NIST: Measurement terminology — Repeatability and random/systematic errors; D.1.1.2–6.
• Exploratorium: Marble Machines Activity Guide — Practical slowing features, securing pieces and repeated tests; pages1–5.

Download this lesson with its diagram and answer (PDF)

Free classroom worksheets

Use this lesson in class or at home with separate student worksheets and a teacher answer key. All three PDFs are free to download, with no sign-up.

• Middle-school worksheet (PDF, 3 pages)
• High-school worksheet (PDF, 4 pages)
• Teacher answer key (PDF, 5 pages)