🍶 Does a full bottle roll down a ramp faster?

My hypothesis

If I change how much water is in the bottle, then how long the bottle takes to roll down the ramp will ______, because ______.

🔊 You fill in the blanks. Think about what the water does inside the bottle as it rolls. A guess is a good because: the test finds out.

Change, measure, keep the same

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 5 times.

What you need

• 🧴 An empty plastic bottle: 1, with its cap
• 🚰 Water from the tap
• 📦 Flat cardboard: the longest flat piece you have, 60 cm or more
• 📚 Some books: 3, about the same thickness
• 🩹 Masking tape, to mark lines
• ⏱️ A stopwatch or a kitchen timer
• 🧽 A sponge or cloth, for wiping up
• 📏 A ruler

Steps

1. Lean the cardboard on a stack of three books to make a ramp.🔊
2. Stick masking tape across the top of the ramp as a start line, and across the bottom as a finish line.🔊
3. Tape marks on the bottle a quarter and half of the way up, using the ruler.🔊
4. Lay the empty bottle on its side on the start line, cap on tight, and let go. Don't push!🔊
5. A helper starts the timer when you let go, and stops it when the bottle crosses the finish line.🔊
6. Write the time in your table. If the bottle rolls off the side, don't count it: try again.🔊
7. Do four more tries with the empty bottle.🔊
8. Fill the bottle to the quarter mark, cap it tight, and do five rolls.🔊
9. Add water to the half mark, cap it tight, and do five rolls.🔊
10. Fill it to the top, cap it tight, and do five rolls.🔊
11. Find the mean for each amount and draw a line graph.🔊
12. Wipe up every spill when you are done.🔊

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

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.

Why it works

🔊 A rolling bottle uses the energy of its fall for two jobs: moving forward and turning round. The water inside is slow to turn with the bottle, so with more water more of the energy goes into moving forward, and a fuller bottle usually rolls down faster. A half-full bottle sloshes, so its times may jump about.

Going further (7th and up): Change a second thing: run the same four amounts down a steeper ramp, and draw both lines on one graph.

Board layout

This project at your grade

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 much water is in the bottle and measured how long the bottle takes to roll down the ramp, in seconds.
• What did you keep the same, and why does that matter? I kept the same bottle with its cap on tight and the same ramp at the same slope the same, so the only difference was how much water is in the bottle.
• How many times did you test it? 5 times at each of my 4 levels.
• If you did it again, what would you change or test next? I'd run the same four amounts down a steeper ramp, and draw 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

• 💧 How much water makes a bottle flip land best?3rd–8th grade · 1 day of testing · free🚗 How things move · 🧂 Kitchen things
• 🎱 Does a higher start make a marble roll faster?3rd–8th grade · 1 day of testing · free🚗 How things move · ✂️ Paper, tape and toys