🫧 How much soap makes the biggest bubble?

My hypothesis

If I change how much soap is in the bubble mix, then how wide the ring is that the bubble leaves will ______, because ______.

🔊 You fill in the blanks. Think about what the soap does to the skin of the water, and whether more soap always helps. 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 3 times.

What you need

• 🫧 Dish soap
• 🚰 Water from the tap
• 🥛 Clear plastic cups, all the same size: 4
• 🥛 A measuring cup
• 🥄 Measuring spoons
• 🥄 A spoon
• 🥤 Straws: 4
• 🍽️ A baking tray or big plate
• 🧽 A sponge or cloth, for wiping up
• 🩹 Masking tape, to mark lines
• 📏 A ruler

Steps

1. Pour half a cup of tap water into each of four clear cups.🔊
2. Stir in dish soap slowly, so no foam forms: a quarter teaspoon, 1 teaspoon, 2 teaspoons and 1 tablespoon.🔊
3. Label each cup with the amount of soap in it.🔊
4. Spread a spoonful of the first mix over a tray to make a wet patch.🔊
5. Dip the end of a straw in the first mix and touch it to the wet patch.🔊
6. Blow out slowly, and never suck in through the straw.🔊
7. Keep blowing slowly until the bubble pops and leaves a ring of tiny drops.🔊
8. Measure straight across the ring, and write the cm in your table.🔊
9. Wipe the tray, use a new straw for each mix, and make three bubbles with each mix.🔊
10. Draw a line graph: soap along the bottom, ring width up the side.🔊

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

🔊 Soap lets water stretch into a thin skin that can wrap around air. With very little soap the skin is weak and pops early. With lots of soap the mix can get thick and foamy, so the biggest bubbles often come from a middle amount.

Going further (7th and up): Change a second thing: stir 1 teaspoon of corn syrup into the best mix, and graph the ring widths with and without it.

Board layout

This project at your grade

From 4th grade up, the table gets a mean column. See every project for 1st 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 soap is in the bubble mix and measured how wide the ring is that the bubble leaves, in cm.
• What did you keep the same, and why does that matter? I kept half a cup of the same tap water in every mix and the same dish soap and the same straw for each mix the same, so the only difference was how much soap is in the bubble mix.
• 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 stir 1 teaspoon of corn syrup into the best mix, and graph the ring widths with and without it.

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

• 🫧 Does dish soap stop oil and water from separating?3rd–8th grade · 1 day of testing · free🧪 Water, ice and mixing · 🧂 Kitchen things
• 🥛 Does whole milk swirl farther than skim milk?2nd–6th grade · 1 day of testing · about $2🧪 Water, ice and mixing · 🧂 Kitchen things

🔨 From the Workshop: this project grows from a Workshop build, with picture steps of its own.