🌈 Does food colouring spread faster in hot water?

My hypothesis

If I change how warm the water is, then how long one drop of colour takes to spread through the whole cup will ______, because ______.

🔊 You fill in the blanks. Think about how fast the water itself is moving inside the cup, even when it looks still. 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

• 🌈 Food colouring: one dark colour
• 🧊 Cold water from the fridge
• 🚰 Water from the tap: left out for an hour, for room temperature
• ♨️ Hot water from the tap or kettle, for a grown-up to pour: hot from the tap, never boiling
• 🥛 Clear plastic cups, all the same size: 3
• 🥛 A measuring cup
• 🌡️ A thermometer (digital, or the red-liquid kind)
• ⏱️ A stopwatch or a kitchen timer

Steps

1. Pour a cup of fridge-cold water into the first clear cup, and room-temperature water into the second.🔊
2. Grown-up: A grown-up pours a cup of hot water into the third cup.🔊
3. Grown-up: A grown-up measures each cup with the thermometer, and you write the temperatures down.🔊
4. Let the cups sit still for a minute, so the water stops swirling.🔊
5. Add one drop of colour to each cup, one after another, and start the timer.🔊
6. Don't stir or bump them: write down the time when each cup has no clear water left.🔊
7. Grown-up: A grown-up empties the cups and pours fresh hot water for each new try.🔊
8. Do the whole test two more times.🔊
9. Find the mean time for each cup, and draw a line graph with temperature along the bottom.🔊

3 steps are 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

🔊 Water is made of tiny bits that never stop jiggling and bumping, even when the cup looks still. In hot water they jiggle faster, so they knock the colour around and spread it sooner. In cold water they move slower, so the colour creeps along and takes much longer.

Going further (7th and up): Change a second thing: use half a cup and a whole cup of water at each temperature, and draw a line for each.

Board layout

This project at your grade

From 4th grade up, the table gets a mean column. See every project for 2nd grade, or print a blank results table.

What a judge will ask

• What did you change, and what did you measure? I changed how warm the water is and measured how long one drop of colour takes to spread through the whole cup, in seconds.
• What did you keep the same, and why does that matter? I kept the same amount of water in each cup and one drop of the same colour the same, so the only difference was how warm the water 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 use half a cup and a whole cup of water at each temperature, and draw a line 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

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