🪣 Which soil lets water through fastest: sand, potting soil or garden soil?

My hypothesis

If I change the kind of soil in the cup, then how much water drips through in one minute will ______, because ______.

🔊 You fill in the blanks. Think about how big the grains of each soil are, and how big the gaps between them must be. 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

• 🏖️ Sand (from a sandbox, or play sand)
• 🪴 Potting soil
• 🟫 Soil dug from the garden or yard
• 🥤 Paper cups with a hole poked in the bottom: 9, all the same
• 🧻 Paper towels: 9 small squares
• 🥛 Clear plastic cups, all the same size: 1, to catch the water
• 🥛 A measuring cup
• 🚰 Water from the tap
• ⏱️ A stopwatch or a kitchen timer

Steps

1. Put a small square of paper towel in the bottom of nine cups with holes, to keep the soil in.🔊
2. Fill three cups with half a cup of sand each, three with potting soil and three with garden soil.🔊
3. Pat each one down gently, the same way.🔊
4. Hold a sand cup over a clear cup, pour in half a cup of water all at once, and start the timer.🔊
5. After one minute, take the soil cup away and measure the water that came through.🔊
6. Write it down, then test the other two sand cups the same way.🔊
7. Test the three potting soil cups and the three garden soil cups.🔊
8. Find the mean for each soil and draw a bar graph.🔊
9. Wash your hands after touching the soil.🔊

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 bar graph, one bar for each thing you tried.

Why it works

🔊 Water drains through the gaps between the grains of soil. Sand has big grains with big gaps, so water usually rushes straight through. Garden soil often holds tiny bits of clay with tiny gaps, and potting soil is spongy and soaks some water up first, so less comes out in a minute.

Going further (7th and up): Change a second thing: mix sand into garden soil at a quarter, a half and three quarters, and draw a line of how much drains through.

Board layout

This project at your grade

From 4th grade up, the table gets a mean column. See every project for 3rd grade, or print a blank results table.

What a judge will ask

• What did you change, and what did you measure? I changed the kind of soil in the cup and measured how much water drips through in one minute, in mL.
• What did you keep the same, and why does that matter? I kept the same amount of soil, patted down the same way and half a cup of water poured in all at once the same, so the only difference was the kind of soil in the cup.
• 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 mix sand into garden soil at a quarter, a half and three quarters, and draw a line of how much drains through.

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

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