Will it float or sink?
A ball of modelling clay sinks… but the same clay shaped into a boat floats! An experiment to become a captain and a scientist.
Age : age 3+
Materials
- A basin of water
- Modelling clay : A piece the size of a ping-pong ball.
- Things from around the house : Cork, spoon, ball, key, apple, pencil, pebble…
- Little treasures for cargo : Marbles, paper clips, coins: with a grown-up watching.
- A sheet and a pencil : To write down predictions.
Steps
Predict and test
- Put the objects by the basin and draw two columns: "floats" and "sinks".
- For each object, the child predicts first, then tests it in the water.
- Compare predictions and results: any surprises?
The boat challenge
- Make a ball of clay and put it in the water: it sinks.
- Take the same clay and flatten it into a little boat with raised sides.
- Put it in gently: it floats!
- Load the boat with marbles one by one. How many before it sinks?
- Try another boat shape to beat the record.
It's not only weight that matters, it's shape. Flattened into a boat, the clay pushes lots of water aside, and the water pushes it back up. As a ball, it pushes too little aside and sinks. That's why very heavy metal ships float.
Add lots of salt to the water and test an egg: in salty water, it floats back up.
If it goes wrong
- The boat lets water in : Raise and thicken the sides.
- The boat tips over : Spread the marbles in the middle.
Safety
- Never leave a child alone near a basin of water, however shallow.
- Marbles and coins out of reach of under-3s.