Why does ice float?

You probably don't even question it! You put ice in a glass, it floats around at the top until it melts. Simple, right?

Is the glass half empty or half full? Scientists say it's completely full

But water is (almost) the ONLY MATERIAL that's solid form floats in its liquid form, because solids are usually denser than liquids. If something starts as a solid and you heat it up, you're exciting the molecules, making the vibrate faster and faster as you raise the temperature - if they get excited enough, they'll break themselves apart. I talked about this a month ago when discussing fog, so check that out if you want more explanation, but the basic idea is this:

Same number of particles in each one, but different densities! Density just means how close the particles are to each other.

So of course that solid would be closer together, just look! Its molecules are all compacted together. But WATER IS A WEIRDO! When it freezes, it forms a crystalline structure that actually spreads the molecules apart a little bit:

 You can see here that it DOES get denser as it gets colder, but once it actually freezes it spreads out!

The densest that H2O can be is actually at 4 degrees Celsius - if it gets colder, it starts to freeze and form that crystalline structure that makes it less dense. This is necessary for life in lakes, because it means that lakes freeze from the top down, leaving space in the water for fish to live until the ice melts again. It's also why the bottom of the deep end of the pool is almost always the cold part, no matter how warm the rest of the water is - the cold sinks to the bottom and never comes back up (because it's not getting colder)!

Double Ouch.

 

Ouch.

Wanna see more frozen things? Check these pictures out!