When you drop ice in water, will it float or sink?
A cold glass of water… and a little ice cube. A heavy rock would go straight to the bottom, plop! Now we hold the ice cube up high… and drop it in. Tap your guess… will the ice float on top, or sink to the bottom? Then watch what the water does!
After you watchWhen you drop ice in water, will it float or sink?
The short answer
Ice floats. When you drop an ice cube into water, it rides on top instead of sinking, with just a little bit poking up above the surface and most of it hidden below.
Try this next
- What if you push the ice cube all the way under? Hold the cube under the water in your mind, then guess what it does the moment you let go — before you watch it pop back up to the top.
- What if you drop in something else, like a grape or a coin? Pick one thing from the kitchen, guess float or sink before it touches the water, then drop it in and watch.
The whole story
How it works
When water freezes into ice, the very same water spreads out a little and takes up more room. Because the ice is roomier than the water around it, the same-size chunk of ice is a touch lighter than the water it would fill — and lighter things ride on top. So the ice cube floats, with about a tenth of it peeking up above the surface and the rest hidden under the water.
What people get wrong
Lots of little kids think hard, solid things always sink — a rock sinks, and ice is hard like a rock, so it should sink too. But ice is special: it is frozen water that spread out and got roomier, so it floats on top of the water instead of dropping to the bottom.
The catch
It is handy that ice floats — it makes a frozen lid on a pond so fish can stay safe and warm underneath all winter. But because freezing makes water spread out and take up more room, it can also push hard enough to crack a pipe or pop the lid off a full bottle left in the freezer.
Questions kids ask
Does ice float or sink in water?
Ice floats. It rides on top of the water with a little bit poking up, and most of the cube hidden just under the surface.
Why doesn't the hard, heavy ice sink like a rock?
Because ice is frozen water that spread out and got a little roomier, so a chunk of ice is lighter than the same amount of water around it — and lighter things float on top.
How much of the ice cube do we see above the water?
Only a little — about a tenth peeks up above the surface, and the other nine-tenths hides below the water.
Talk about it
- Before we drop it in — do you think the ice will float on top or sink to the bottom?
- A rock sinks but the ice floats. What do you think makes the ice different?
- Where do you think the rest of the ice cube is, under the water?
For grown-ups
Water is unusual: most things get denser when they freeze, but water spreads into an open crystal and gets about 9% less dense, so ice floats and roughly a tenth of it rides above the surface. For ages 4–6, keep it to one big idea they can see — ice rides on top — and let the cube bob in front of them before naming anything.
Keep going
What else makes you wonder?
- What other cold things might float in your drink instead of sinking?
- Where does all the rest of the ice cube go when it sits under the water?
- What would your drink be like if the ice sank to the very bottom?