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Asked by #french fries to Andrew, Jade, Jessica, Kevin, Lynn on 14 Jun 2015.
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Kevin Honeychurch answered on 14 Jun 2015:
Anything that displaces a greater weight of water than its own weight will float, so pumice stone floats
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Jess Wade answered on 14 Jun 2015:
Think about a rubber duck in the bath or a lilo in a swimming pool. When we put them on top of the water, some of the water has to move out of the way. If we weigh out the water that has to move when the duck sits on the bath or we put the lilo on the pool, that would weight more than the weight of the lilo or the weight of the duck- so both things float.
There are special rocks called ‘pommie’ stones- their scientific name is a pumice stone. You might have found them on beaches or your mum might rub them on her feet to make them smoother! They look like little white sponges and don’t weight very much. It’s actually a really cool stone and is made in a volcano !!! Because of how quickly it cools when it shoots out of the volcano it changes shape so much that little bubbles form inside it. So many bubbles form the pommie stones are about 90 % empty space- so they move much more water than they weigh and float on the surface. Try find one when you next go to the beach!
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Andrew Fensham-Smith answered on 15 Jun 2015:
Things float when they are lighting than the amount of water they would occupy. So imagine you have a ball of something – lets say metal – if there was a ball the exact same size, made of water, it would weigh less. Therefore, because the metal weighs more than the same size of water, it will sink. Whereas something which floats, like a inflated balloon, weighs less than the same size of water. So we need to find a rock which is lighter than if we had the same size of water! There is one – it’s called Pumice and it’s made by volcanos flinging them out when they erupt. The lava which was under really, really high pressure suddenly expands and gets lots of little bubbles inside. These bubbles make the stone weigh much less than it would if it cooled more slowly with no bubbles. Therefore this stone weighs less than the same size of water, and so it floats. Makes sense!
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Jade Owen answered on 15 Jun 2015:
Pumice is a type of rock that floats. It’s made from special lava from a volcano.
All lava from volcanoes is very gassy (think of a glass of coke cola or lemonade!). As the lava leaves the volcano the gas inside is able to bubble out as there is less pressure (think of when you shake a bottle of fizzy drink then take the top off!).
The lava that makes the pumice is really really gassy thanks to lots of water and when it exits the volcano it cools really quickly trapping the gas bubbles inside! This helps make the pumice float.
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