⛰️ Does a steeper hill wash away more soil?

My hypothesis

If I change how steep the hill is, then how deep the washed-away mud is in the cup after 15 minutes will ______, because ______.

🔊 You fill in the blanks. Think about what the water does as it speeds up, and what it can pick up and carry. 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 3 levels 3 times.

What you need

• 📦 A shoebox: a shoebox: you use its lid
• 🥈 Foil
• 🩹 Masking tape, to mark lines
• 📚 Some books: 3, all about the same thickness
• 🟫 Soil dug from the garden or yard: 9 cups, dry
• 🥛 A measuring cup
• 🚰 Water from the tap
• 🥣 A big bowl: a big one
• 🥛 Clear plastic cups, all the same size: 9 tall ones
• 📏 A ruler

Steps

1. Grown-up: A grown-up cuts the rim off one short end of a shoebox lid, to make a slide with an open end.🔊
2. Press foil into the lid and tape it down, so water runs along the foil and not into the cardboard.🔊
3. Work outside or at the sink: rest the slide on a counter or table, its open end over a big bowl.🔊
4. Prop the high end of the slide on one book.🔊
5. Spread one cup of dry garden soil over the top half of the slide, and pat it flat.🔊
6. Pour one cup of water slowly onto the top of the soil while you count to ten.🔊
7. Pour the muddy water from the bowl into a tall clear cup, and label it with the number of books.🔊
8. Do two more runs on one book, with fresh soil and a wiped-out slide each time.🔊
9. Prop the slide on two books and do three runs, then on three books and do three runs.🔊
10. Leave all nine cups still for 15 minutes so the mud can settle.🔊
11. Stand a ruler against each cup, measure how thick the mud is on the bottom in mm, and write it down.🔊
12. Muddy water is never for drinking: pour it onto the garden when you've finished.🔊
13. Find the mean mud depth for each slope and draw a line graph.🔊
14. Wash your hands after touching the soil.🔊

One step is a grown-up's, marked above. 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

🔊 Running water pushes tiny bits of soil along with it, and the faster the water runs, the more it can carry. On a steeper slope gravity pulls the water down faster, so it often carries away more soil. That is why farmers plant steep hillsides and builders cut them into steps, to slow the water down.

Going further (7th and up): Change a second thing: keep the steepest slope and change the soil to sand, potting soil and garden soil, and graph the mud depth for each.

Board layout

This project at your grade

Every grade this project fits works out a mean. See every project for 4th grade, or print a blank results table.

What a judge will ask

• What did you change, and what did you measure? I changed how steep the hill is and measured how deep the washed-away mud is in the cup after 15 minutes, in mm.
• What did you keep the same, and why does that matter? I kept the same amount of dry garden soil, patted down the same way and one cup of water poured at the same speed, in the same place the same, so the only difference was how steep the hill is.
• How many times did you test it? 3 times at each of my 3 levels.
• If you did it again, what would you change or test next? I'd keep the steepest slope and change the soil to sand, potting soil and garden soil, and graph the mud depth for each.

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

• 🌱 Do grass roots stop soil washing away?4th–8th grade · 14 days of testing · about $3🌦️ Growing and weather · 🌱 Outside and plants
• 🪣 Which soil lets water through fastest: sand, potting soil or garden soil?3rd–8th grade · 1 day of testing · about $1🌦️ Growing and weather · 🌱 Outside and plants