Percentage Uncertainty

Lab Brief #3

🎯 Your mission

Set it up. Test it. Be amazed.

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

Absolute uncertainty is the ± on a measurement; percentage uncertainty is that divided by the measurement, times 100. The same ±1 mm matters far more on a 5 mm length than on a 500 mm one, which is why measuring a bigger sample improves precision.

Key words

absolute uncertainty
The ± range on a single measurement, in the measured units.
percentage uncertainty
Absolute uncertainty divided by the measurement, as a percentage.

Make a hypothesis first

Before you start: write down what you think will happen, and why.

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

ream of paper
ruler with millimetre divisions
calculator

⚠️ Safety first

Have an adult check your set-up before you start, and tidy everything away afterwards.

Step 1 of 4 · Read

Think about what you just learned: say what "absolute uncertainty" and "percentage uncertainty" mean in your own words before you start.

Step 2 of 4 · Do

Measure the thickness of one sheet of paper directly, then measure 200 sheets and divide. Calculate percentage uncertainty for both methods and explain which is better and why.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

A measurement of 50 mm ± 1 mm has a percentage uncertainty of:

How sure are you?😐 maybe

Question 2 of 2

Measuring 200 sheets instead of one reduces:

How sure are you?😐 maybe

Mind = blown

🔬 The more you look, the more nature shows you.

Nice work!

You got 0 of 2 right.

Next: Writing a Conclusion That the Data Supports All lessons

🎯

Next Smart Experiment

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✨ More to explore

🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.

🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.

👨‍👩‍👧 For the dinner table: “What's the most surprising thing you learned today?”

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Percentage Uncertainty

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