Image: James St John I Flicker.com I CC BY-2.0
Floating Rock?!
WHAT YOU’LL NEED:
- Large bowl or bucket filled with cold water
- Three different–sized rocks or pebbles
- Pumice
WHAT TO DO:
1.
Look closely at the different rocks. Which is the heaviest? Which is the lightest?
Are there any other differences?
2. Predict which stone(s) you think will float or sink.
3 Place the stones in the water and observe what happens. Do they float or sink?
4. Place the pumice in the water. What happens?
HOW DOES IT WORK?
An object will float if it is less dense than its surroundings, just like the pumice.
Even though pumice is a stone, it has tiny pockets of air caused by
gas bubbles created during its formation. These air pockets make pumice very light.
Have another look at the pumice. Is is still floating?
As the pumice floats, the pockets of air start filling up with water. The pumice becomes
increasingly dense and will eventually sink.