Pages Menu
Categories Menu

Posted by on Sep 6, 2015 in Tell Me Why |

Why Does Ice Float?

Why Does Ice Float?

Ice is able to float because it is lighter than water. Water greatly expands as it freezes into ice. Ten quarts of water produce about eleven quarts of ice. Thus, ice is much lighter than water and rises to the surface. When an ice cube is floating, about one-tenth of it is above the surface. Likewise, ice shrinks about one-tenth in size as it melts.

Therefore, the water from a melted ice cube will take up only as much space as the ice cube took up when it was floating. This explains why the water level in a glass doesn’t rise as the ice melts.

A substance floats if it is less dense, or has less mass per unit volume, than other components in a mixture. For example, if you toss a handful of rocks into a bucket of water, the rocks, which are dense compared to the water, will sink.

The water, which is less dense than the rocks, will float. Basically, the rocks push the water out of the way, or displace it. For an object to be able to float, it has to displace a weight of fluid equal to its own weight.

Ice floats because it is less dense than liquid water. In other words, ice takes up more space than water, so a liter of ice weighs less than liter water. The heavier water displaces the lighter ice, so ice floats to the top.

One consequence of this is that lakes and rivers freeze from top to bottom, allowing fish to survive even when the surface of a lake has frozen over. If ice sank, the water would be displaced to the top and exposed to the colder temperature, forcing rivers and lakes to fill with ice and freeze solid.

Content for this question contributed by Elizabeth Rabara, resident of Santa Maria, Ilocos Sur, Philippines