What it shows
Rocks and pebbles come from bigger rocks that wear down. They differ in colour, smoothness and weight, and we can sort them by these properties.
The science
Large rocks are broken by sun, rain and wind into small pieces. Water rolls pebbles over each other, so river pebbles become smooth and round. Rocks made of different minerals have different colours and weights. Sorting by a property lets us see these differences.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Ten small pebbles from a garden, river bank or road side (free)
- An egg carton to hold them
- A bowl of water and a cloth
- A kitchen or hand balance if possible
- Paper labels and pencil
Safety
For this project: Wash your hands after touching soil and stones. An adult must come when collecting near a river, road or building site.
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.
Collect ten small pebbles of different looks and bring them home.
Wash them in the bowl with water and dry them with a cloth.
Put one pebble in each cup of the egg carton and give each a number.
Sort them by colour: light, dark and spotted.
Sort them again by touch: smooth and rough. Write S or R on the label.
Compare their weight by holding two in your hands, or by using a balance.
Arrange the pebbles from the lightest to the heaviest.
Wet one smooth and one rough pebble and say how the colour changes.
What you should see
You have ten numbered pebbles sorted three ways and a lightest to heaviest line-up. Wet pebbles look darker and brighter.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why are river pebbles smooth?
Moving water rubs them against each other for many years.
2Which two things did you use to sort?
Colour, feel and weight. Name two from your tray.
3Are all rocks the same inside?
No, they are made of different minerals.
4Why did the wet pebble look darker?
Water makes the surface shine and show richer colour.
Take it further
Test whether each pebble sinks or floats and whether any is magnetic.
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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