What it shows
Some fruits and vegetables float and some sink in water, depending on how much of the body is air and how heavy it is for its size. Predicting before testing is how scientists work.
The science
An object floats if it is lighter than the same amount of water. Apples have tiny pockets of air, so they float. A potato is solid and denser than water, so it sinks. A whole orange floats, but a peeled orange sinks, because the peel holds air and acts like a life jacket.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A large bowl or bucket of water
- Eight fruits and vegetables, like an apple, an orange, a lemon, a tomato, a potato, a carrot, a cucumber and a chilli (from the kitchen)
- A chart on paper with columns: name, I think, result
- A pencil
- A towel
Safety
For this project: An adult must supervise near water. Wipe up spills so no one slips. Do not eat the tested fruits unless washed again.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Fill the bowl with water until it is about three quarters full.
Write the name of each fruit and vegetable in the first column of the chart.
For each one, write your guess in the second column: sink or float.
Drop the first fruit gently into the water and watch what happens.
Write the result in the third column and tick if your guess was right.
Test all the others one by one and wipe up any splashes.
Peel the orange and test it again and see what changes.
Count how many guesses you got right and say why peeled orange sinks.
What you should see
Apple, orange and lemon float, while potato, carrot and tomato may sink. Your chart shows your guesses and the real results. A peeled orange sinks while the unpeeled one floats.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What does it mean to float?
To stay on top of the water without sinking.
2Why does the apple float?
It has air inside and is lighter than the same amount of water.
3Why does a peeled orange sink?
The peel holds air that helped it float. Without it the orange is heavier than water.
4Why did we guess before testing?
To check our thinking against the evidence.
Take it further
Cut a potato into a boat shape and see whether it can float if it holds some air.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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