Science Fair

Grown-ups

How much does a rubber band stretch with each extra weight?

5th–8th grade · 1 day of testing · free · ages 10 to 14 · 45 minutes a sitting

  • 👶 Small parts
What you need for the rubber band stretch project: rubber bands, all the same size, a small paper cup with a string handle, pennies, a pencil

My hypothesis

If I change how many pennies hang on the band, then how far the rubber band stretches will ______, because ______.

You fill in the blanks. Think about whether every extra 10 pennies adds the same amount of stretch. A guess is a good because: the test finds out.

Change, measure, keep the same

CHANGE

how many pennies hang on the band: 10 pennies, 20 pennies, 30 pennies, 40 pennies

MEASURE

how far the rubber band stretches, in cm

KEEP THE SAME

  • the same rubber band
  • the same cup
  • measuring from the same point every time

Scientists call the thing you change the independent variable and the thing you measure the dependent variable. The things you keep the same are the controls: if one of them changed too, you wouldn't know which change made the difference. Try each of the 4 levels 3 times.

What you need

  • Rubber bands, all the same size: 2
  • A small paper cup with a string handle
  • Pennies: 40
  • A pencil
  • 🩹 Tape
  • 📏 A ruler

Steps

  1. Tape a pencil to the edge of a table so it sticks out.
  2. Loop the rubber band over the pencil and hang the empty cup from it.
  3. Measure the band from the pencil to the cup's handle: that's your start length.
  4. Put 10 pennies in the cup and measure again.
  5. Take the pennies out, let the band rest a minute, and do it twice more.
  6. Do three tries each with 20, 30 and 40 pennies.
  7. Take away the start length to find how much it stretched each time.
  8. Plot the points and see whether they make a straight line.

Every step is one you can do yourself, with a grown-up nearby. Write each number down straight away, in the table below, so nothing is lost.

Your results table

MY RESULTSPeabody 🦉 peabody.kids/science-fair

Name ______________________ Fair day ____________

Question: How much does a rubber band stretch with each extra weight?

I changed: Pennies in the cup   I measured: how far the rubber band stretches (cm)

Pennies in the cupTry 1 (cm)Try 2 (cm)Try 3 (cm)Mean
10 pennies
20 pennies
30 pennies
40 pennies

MY GRAPH (a line graph: pennies in the cup along the bottom, cm up the side)

What I noticed: ______________________________________________

From 4th grade, add the tries for each level and divide by how many there were: that's the mean, and it goes in the last column. Then draw a line graph, because the thing you change is a number that goes up.

📊 Make my graph🖨 Print the whole packet (9 pages)

Why it works

A rubber band stretches more when more weight pulls on it. For a while, each extra 10 pennies stretches it about the same amount, so the points sit on a straight line. Pull too hard and the band gets tired and leaves the line, which is why you let it rest between tries.

Going further (7th and up): Change a second thing: hang the same pennies from two bands side by side, and plot both lines on one graph.

Board layout

MY BOARD · 36 × 48 in tri-foldPeabody 🦉 peabody.kids/science-fair
  1. ❓ Question (10 × 8 in): How much does a rubber band stretch with each extra weight?
  2. 💭 Hypothesis (10 × 9 in): If I change how many pennies hang on the band, then how far the rubber band stretches will ______, because ______.
  3. 🧺 Materials (10 × 12 in): 4 things: see your list.
  4. 🪜 Steps (22 × 9 in): 8 steps, three tries at each level.
  5. 📊 Results (22 × 16 in): Your table (Pennies in the cup down the side, tries across) and your line graph.
  6. ✅ Conclusion (10 × 14 in): My hypothesis was right / partly right / not right. I know because…

Materials to list: Rubber bands, all the same size; A small paper cup with a string handle; Pennies; A pencil.

Bring photos or drawings of your test. Nothing wet, hot, powered or alive on the table.

This project at your grade

4th–6th gradeTries: three at each level. The table: units in the header and a mean column. The graph: a bar graph, or a line for a number that grows. The conclusion: right, partly or not, and the numbers that show it.
7th grade and upTries: three or more at each level. The table: a mean for every level of both tests. The graph: a graph with two lines or two sets of bars. The conclusion: the numbers, what might have gone wrong, and a next question. Second variable: hang the same pennies from two bands side by side, and plot both lines on one graph.

Every grade this project fits works out a mean. See every project for 5th grade, or print a blank results table.

What a judge will ask

  • What did you change, and what did you measure? I changed how many pennies hang on the band and measured how far the rubber band stretches, in cm.
  • What did you keep the same, and why does that matter? I kept the same rubber band and the same cup the same, so the only difference was how many pennies hang on the band.
  • How many times did you test it? 3 times at each of my 4 levels.
  • If you did it again, what would you change or test next? I'd hang the same pennies from two bands side by side, and plot both lines on one graph.

Make it yours

Keep this project on this device and Peabody counts down to your fair day, with a plan for each day. Nothing is sent anywhere.

Try next

👨‍👩‍👧 For grown-ups and teachers: how much to help, the safety rules, and running a school fair. Science fair v0.16.1 · Checked .

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