Why Does Ice Float?
(Lansing State Journal 4/8/98) In order to answer this question we first have to understand why anything floats. This question is easiest to understand in the case of water. When you put a bunch of marbles into a bowl of water, you can see the level of the water rise. In fact , the marbles are pushing the water out of the way, that is, displacing the water. The marbles sink because they are more dense than the water. In order for an object to float, it must be able to displace a weight of fluid equal to its own weight. The amount of water that is displaced by a marble weighs less than the marble, so the marble sinks. As we discussed last week, water expands when it freezes, becoming ice. So when an ice cube floats in a bowl of water, the ice displaces an amount of water equal to its weight, so it floats. This property of ice is very important since the top of a lake can freeze without sinking. If the ice sunk, then the entire lake would fill up with ice and all the fish would be frozen
” THE ANSWER: Water has different states, including a liquid and a solid form. And since the solid form–ice–is less dense than liquid water, ice can float. WHAT YOU NEED: Plastic cups, water, and ice cubes. HOW TO DO IT: First explain to your students that all things (matter) take up space and have weight. When water freezes into ice, it takes up more space. Demonstrate this by pouring an equal amount of water into two cups, and freezing one overnight. The cup holding frozen water will be more “full” than the water cup. But both cups still weigh the same amount. That means the water’s weight gets spread out over a larger space when it freezes into ice. Ask students what they think will happen if you placed an ice cube into the water. Will the cube sink or float? Check their predictions by having them carefully drop a cube into water. Have students test out other objects’ density relative to water. Ask students to choose a small classroom object, such as a piece of chalk, a paper clip
Many people have observed that ice floats in water, which seems to defy common sense, as most people expect solid forms of liquids to be heavier than their liquid forms. Like everything else that floats, ice floats because it is less dense than water, demonstrating the property of buoyancy. In addition, ice is also an illustration of the fascinating properties of water, a liquid which behaves in some very unusual ways. When you see ice float, you are looking at a demonstration of the scientific principle of buoyancy. Objects are said to be buoyant when they are able to displace their own weight in water before sinking. As the object settles in the water, an equal force pushes up against the bottom of the object, causing it to float, rather than sink. When the surface area and density of a substance are right, that substance floats rather than sinking to the bottom. In the case of most liquids, the cooler the liquid is, the more dense it becomes. Water, however, reaches its maximum dens
As we approach winter, depending upon which part of the country we live, we will encounter freezing temperatures. Most of the country will enjoy the poetry and beauty – and the needed respites – of the ice and snow of this special season. (Our friends in Southern California are generally denied the poetry of winter unless they brave the stresses of the freeways to reach the mountains. But they can also observe the essentials of this article by watching an ice cube in a glass of water. Our friends in the Southern Hemisphere experienced what we are going to be talking about six months ago.) Have you ever noticed that ice floats? Why? Virtually every material substance contracts when it cools. As it gets warmer, the molecules increase their vibrational energy and require more room: the substance therefore expands as it warms. And, conversely, it contracts as it cools. Materials decrease in volume as they get colder. Water is the astonishing exception. It expands when it freezes into a sol
